What Happens When Heredity Follows Different Rules?

Patterns of Heredity and Human GeneticsA Look at Genetic ComplexitiesChapter 12 Notes1What happens when heredity follows different rules? The Exceptions to Mendels RulesSection 12.2At the end of this lesson, YOU will be able to:Distinguish between alleles for incomplete dominance and codominance.Explain the patterns of multiple allelic and polygenic inheritance.Analyze the pattern of sex-linked inheritance.Summarize how internal and external environments affect gene expression.Section ObjectivesRemember Punnett Squares

Heterozygous Chin Dimple (male)XNo Chin Dimple(female)DdddDdddHis 4 conclusions were:The Rule of Unit FactorsThe Rule of DominanceThe Law of SegregationThe Law of Independent AssortmentRemember Mendel?

http://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpg

In genetics, dominance describes a specific relationship between the effects of different versions of a gene (alleles) on a trait or phenotype. Animals (including humans) and plants are diploid (see ploidy), with two copies of each gene, one inherited from each parent. If the two copies are not identical (not the same allele), their combined effect may be different than the effect of having two identical copies of one or the other allele. But if the combined effect is the same as the effect of having two copies of one of the alleles, we say that allele's effect is dominant over the other.For example, having two copies of one allele of the EYCL3 gene causes the eye's iris to be brown, and having two copies of another allele causes the iris to be blue. But having one copy of each allele leads to a brown iris, thus the brown allele is said to be dominant over the blue allele (and the blue allele is said to be recessive to the brown allele).We now know that in most cases a dominance relationship is seen when the recessive allele is defective. In these cases a single copy of the normal allele produces enough of the genes product to give the same effect as two normal copies, and so the normal allele is described as being dominant to the defective allele. This is the case for the eye color alleles described above, where a single functional copy of the brown allele causes enough melanin to be made in the iris that the eyes appear brown even when paired with the non-melanin-producing blue allele.Dominance was discovered by Mendel, who introduced the use of uppercase letters to denote dominant alleles and lowercase to denote recessive alleles, as is still commonly used in introductory genetics courses (e.g. B b for alleles causing brown and blue eyes). Although this usage is convenient it is misleading, because dominance is not a property of an allele considered in isolation but of a relationship between the effects of two alleles. When geneticists loosely refer to a dominant allele or a recessive allele, they mean that the allele is dominant or recessive to the standard allele.Geneticists often use the term dominance in other contexts, distinguishing between simple or complete dominance as described above, and other relationships. Relationships described as incomplete or partial dominance are usually more accurately described as giving an intermediate or blended phenotype. The relationship described as codominance describes a relationship where the distinct phenotypes caused by each allele are both seen when both alleles are present.

5Sometimes, patterns of inheritance are not as simple as Mendels Rules imply.The exceptions to Mendels Rules are when nature uses a different method of determining traits.Exceptions to Mendels Rules

The Law of Independent Assortment can be broken when genes are found close together on the same chromosome.The genes will appear linked, or show up together.The closer the genes are to each other the more they will be inherited together.Gene Linkage

Physical Mapping is the process of determining how DNA contained in a group of clones overlap without having to sequence all the DNA in the clones. Once the map is determined, we can use the clones as a resource to efficiently contain stretches of genome in large quantity. This type of mapping is more accurate than genetic maps.In maps based on a genetic fingerprinting of the clones, the stretches of DNA are identified according to how they are cut by a restriction enzyme. Once cut, the DNA fragments are separated by electrophoresis. The resulting pattern of DNA migration (ie. its fingerprint) is used to identify what stretch of DNA is in the clone. By analysing the fingerprints, contigs are assembled by automated (FPC) or manual means (Pathfinders) into overlapping DNA stretches. Now a good choice of clones can be made to efficiently sequence the clones to determine the DNA sequence of the organism under study (seed picking).Macrorestriction is a type of physical mapping wherein the high molecular weight DNA is digested with a restriction enzyme having a low number of restriction sites.Outlined above are alternative ways to investigate to create genetic maps (radiation hybrids, STS,...).Genes can be mapped prior to the complete sequencing of a by independent approaches like in situ hybridization. Once the genome has been sequenced, in-silico approaches perform the gene finding. The such suggested genes are compared with the experimental evidence for the respective gene.

7Usually, a dominant gene produces a protein for the trait.The recessive allele either produces a nonfunctional protein or no protein at all.So we see the dominant trait in hybrids because it is the only trait expressing a protein.Breaking the Rule of Dominance

ProteinDNAmRNAmRNAMany genes code for enzymes. Consider the case where someone is homozygous for some trait. Both alleles code for the same enzyme, which causes a trait. Only a small amount of that enzyme may be necessary for a given phenotype. The individual therefore has a surplus of the necessary enzyme. Let's call this case "normal". Individuals without any functional copies cannot produce the enzyme at all, and their phenotype reflects that. Consider a heterozygous individual. Since only a small amount of the normal enzyme is needed, there is still enough enzyme to show the phenotype. This is why some alleles are dominant over others.In the case of incomplete dominance, the single dominant allele does not produce enough enzyme, so the heterozygotes show some different phenotype. For example, fruit color in eggplants is inherited in this manner. A purple color is caused by two functional copies of the enzyme, with a white color resulting from two non-functional copies. With only one functional copy, there is not enough purple pigment, and the color of the fruit is a lighter shade, called violet.Some non-normal alleles can be dominant. The mechanisms for this are varied, but one simple example is when the functional enzyme is composed of several subunits. In this case, if any of the subunits are nonfunctional, the entire enzyme is nonfunctional. In the case of a single subunit with a functional and nonfunctional allele (heterozygous individual), the concentration of functional enzymes is 50% of normal. If the enzyme has two identical subunits, the concentration of functional enzyme is 25% of normal. For four subunits, the concentration of functional enzyme is about 6% of normal. This may not be enough to produce the wild type phenotype. There are other mechanisms for dominant mutants.

8When heterozygous individuals show an intermediate phenotype between the two homozygous phenotypes.Having one copy of a gene does not produce enough protein to completely mask the recessive allele.Incomplete Dominance

http://www.miracosta.edu/home/rmooney/Mendelian%20genetics_files/slide0015_image033.jpgDiscovered by Karl Correns, incomplete dominance (sometimes called partial dominance) is a heterozygous genotype that creates an intermediate phenotype. In this case, only one allele (usually the wild type) at the single locus is expressed, and the expression is doseage dependent. Two copies of the gene produce full expression, while one copy of the gene produces partial expression in an intermediate phenotype. A cross of two intermediate phenotypes (= monohybrid heterozygotes) will result in the reappearance of both parent phenotypes and the intermediate phenotype. There is a 1:2:1 phenotype ratio instead of the 3:1 phenotype ratio found when one allele is dominant and the other is recessive. This lets an organism's genotype be diagnosed from its phenotype without time-consuming breeding tests.

9SnapdragonsIf you cross a red flower and a white flower, the resulting hybrid will be pink.RR = red flowerrr = white flowerRr = pink flowerIf you cross two pink flowers (Rr), you get:25% Red Flowers50% Pink Flowers25% White FlowersIncomplete DominanceRRrrRrRrRrRrRrRrRrRrRRrrThe taxonomy of this genus is disputed at present. At one extreme, ITIS recognises only the Old World species of sect. Antirrhinum in the genus, listing only the Garden Snapdragon A. majus (the only species in the section naturalised in North America). At the other, Thompson (1988) places 36 species in the genus; many modern botanists accept this circumscription. New species also continue to be discovered (see e.g. Romo et al., 1995).Recent research in the molecular systematics of this group, and related species, by Oyama and Baum (2004), has confirmed that the genus as described by Thompson is monophyletic, provided that one species (A. cyathiferum) is removed to a separate genus, and two others (previously listed as Mohavea confertiflora and M. breviflora) are included. The species list at the right follows these conclusions. It is widely agreed that this broad group should be subdivided into three or four subgroups, but the level at which this should be done, and exactly which species should be grouped together, remain unclear. Some authors continue to follow Thompson in using a large genus Antirrhinum, which is then divided into several sections; others treat Thompson's genus as a tribe or subtribe, and divide it into several genera.If the broad circumscription is accepted, its sections are as follows:Section Antirrhinum: about 20 Old World species of perennial plants, the type Antirrhinum majus, mostly native to the western Mediterranean region with a focus on the Iberian Peninsula. Section Orontium: two to six species, also Mediterranean. The species in this section, including the type Lesser Snapdragon A. orontium, are often treated in the genus Misopates. Section Saerorhinum: about 16 New World species, mostly annual plants and mostly native to California, though species are found from Oregon to Baja California Sur and as far east as Utah. Like other authors, Thompson placed A. cyathiferum in this section, but Oyama and Baum, following earlier authors, suggest that it should be reclassified in genus Pseudorontium, while Mohavea confertiflora and M. breviflora should be included. Some authors classify the species in this section into the genera Sairocarpus, Howelliella and Neogaerrhinum. The Garden Snapdragon is an important garden plant; cultivars of this species have showy white, crimson, or yellow bilabiate flowers. It is also important as a model organism in botanical research, and its genome has been studied in detail.While Antirrhinum majus is the plant that is usually meant if the word "snapdragon" is used on its own, many other species in the genus, and in the family Scrophulariaceae more widely, have common names that include the word "snapdragon".

10HairStraight (HH)Wavy (Hh)Curly (hh)

Incomplete Dominance

Head hair is a type of hair that is grown on the head (sometimes referring directly to the scalp). The most noticeable part of human hair is the hair on the head, which can grow longer than on most mammals and is more dense than most hair found elsewhere on the body. The average human head has about 100,000 hair follicles. [1] Its absence is termed alopecia, commonly known as baldness. Anthropologists speculate that the functional significance of long head hair may be adornment, a by-product of secondary natural selection once other somatic hair had been lost. Another possibility is that long head hair is a result of Fisherian runaway sexual selection, where long lustrous hair is a visible marker for a healthy individual (with good nutrition, waist length hairapproximately 1 meter or 39 inches longwould take around 84 months, or about 7 years, to grow). Each follicle can grow about 20 individual hairs in a person's lifetime. [2] Average hair loss is about 100 strands a day. The average human scalp measures approximately 120 square inches (770 cm). These values are also reported by Desmond Morris[4] although it is not clear if these apply to both men and women.Average number of head hairs (Caucasian) [3]color number of hairs diameter Blonde 146,000 11500th to 1500th inch 17 to 51 micrometers Black 110,000 1400th to 1250th inch 64 to 100 micrometers Brunette 100,000 variable variable Red 86,000 variable variable11When a heterozygous individual shows the phenotypic traits of both alleles.Both alleles produce a protein, which are seen in the hybrids.The traits do not blend!Codominance

In codominance, neither phenotype is recessive. Instead, the heterozygous individual expresses both phenotypes. A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. The A and B alleles are codominant with each other. When a person has both an A and a B allele, the person has type AB blood.When two persons with AB blood type have children, the children can be type A, type B, or type AB. There is a 1A:2AB:1B phenotype ratio instead of the 3:1 phenotype ratio found when one allele is dominant and the other is recessive. This is the same phenotype ratio found in matings of two organisms that are heterozygous for incomplete dominant alleles.

Roan, caused by the roan gene, (R), consists of single white hairs intermingled with the base color of a horse. Roaning gives the horse a lightened appearance, while the mane, tail, head and legs tend to remain darker, close to the original base color. It is a dominant gene, meaning that any individual with at least one copy of the R gene trait will be roan. An implication of the gene's dominance is that at least one parent must be a roan in order to pass the gene on it cannot appear in offspring of two non-roan parents, even if they have roan ancestors.Roan horses are born roan and stay that way throughout life. Though there may be some changes in coat color when a foal sheds out its first "baby" coat, and color variation from summer to winter, but the horse will not progressively lighten each year the way a gray does. A roan and a gray can be distinguished from one another because a gray is born dark, and lightens more each year, usually on the head first, while a roan is born with intermixed hairs, and the head stays darker than the body.

12Feather Color in ChickensA black chicken would be BB.A white chicken would be WW.A hybrid, BW, would have a checkered appearance.Both white and black pigments are seen in the offspring.CodominanceBBWWWBWBBWBWBWBWBWBWBBWW

Sickle CellCodominance

InheritanceSickle-cell conditions are inherited from parents in much the same way as blood type, hair color and texture, eye color and other physical traits. The types of haemoglobin a person makes in the red blood cells depend upon what haemoglobin genes the person anaemia ("SS" in the diagram) and the other is Normal (AA), all of their children will have sickle cell trait (AS). If one parent has sickle-cell anaemia (SS) and the other has Sickle Cell Trait (AS), there is a 50% chance (or 1 out of 2) of a child having sickle cell disease (SS) and a 50% chance of a child having sickle cell trait (AS). When both parents have sickle cell trait (AS), they have a 25% chance (1 of 4) of a child having sickle cell disease (SS), as shown in the diagram. Sickle-cell anemia appears to be caused by a recessive allele. Two carrier parents have a one in four chance of having a child with the disease. The child will be homozygous recessive.However, it has been argued that the allele, although appearing outwardly recessive, is in fact co-dominant, due to the resistance to a malaria which is obtained by those of the AS genotype. Since a separate phenotype from that of Normal (AA) has therefore been expressed, it is impossible to argue that the S allele is homozygous recessive.

14When a trait is controlled by more than two alleles.Each individual only owns two alleles, but others in the population may possess different types.Multiple Alleles

An allele (pronounced /lil/ (UK), /lil/ (US)) (from the Greek , meaning each other) is one member of a pair or series of different forms of a gene. Usually alleles are coding sequences, but sometimes the term is used to refer to a non-coding sequence. An individual's genotype for that gene is the set of alleles it happens to possess. In a diploid organism, one that has two copies of each chromosome, two alleles make up the individual's genotype.An example is the gene for blossom colour in many species of flower a single gene controls the colour of the petals, but there may be several different versions (or alleles) of the gene. One version might result in red petals, while another might result in white petals. The resulting colour of an individual flower will depend on which two alleles it possesses for the gene and how the two interact.

15Fur Color in RabbitsC = Dominant allelech = Himalayan furcch = Chinchilla furca = Albino furMultiple Alleles

C

ch

cch

ca

cbcb- Bugs BunnyBugs is noted for his feuds with Elmer Fudd, Yosemite Sam, Marvin the Martian, Beaky Buzzard, Daffy Duck, Witch Hazel, Rocky and Mugsy, Wile E. Coyote and a host of others. Bugs is the traditional winner of these conflicts, a plot pattern which recurs in Looney Toons films directed by Chuck Jones. Concerned that viewers would lose sympathy for an invariably triumphant protagonist, Jones had the antagonist characters repeatedly bully, cheat or threaten Bugs. When offended by the antagonism, Bugs' catchline was "Of course you realize, dis means war!" (this line was taken from Groucho Marx)[2] or, alternatively, "You realize this is not going to go unchallenged!". Other directors, such as Friz Freleng, characterized Bugs as altruistic. When Bugs meets other successful characters, (such as Cecil Turtle in Tortoise Beats Hare, or, in World War II, the Gremlin of Falling Hare) his overconfidence becomes a disadvantage.Bugs Bunny's nonchalant carrot-chewing standing position, as explained by Chuck Jones, Friz Freleng, and Bob Clampett, originated from a scene in the film It Happened One Night, in which Clark Gable's character leans against a fence, eating carrots rapidly and talking with his mouth full to Claudette Colbert's character. This scene was well-known while the film was popular, and viewers at the time likely recognized Bugs Bunny's behavior as satire.[6]The carrot-chewing scenes are generally followed by Bugs Bunny's most well-known catchphrase, "What's up, Doc?". The phrase was written by director Tex Avery for his first Bugs Bunny short, 1940's A Wild Hare. Avery explained later that it was a common expression in Texas, where he was from, and that he did not think much of the phrase. When the short was first screened in theaters, the "What's up, Doc?" scene received a tremendously positive audience reaction.[7] As a result, the scene became a recurring element in subsequent films and cartoons. However, the phrase is not beyond editing, the most notable of which being whenever Bugs greets Daffy: "What's up, Duck?"Several Chuck Jones shorts in the late 1940s and 1950s depict Bugs travelling via cross-country (and, in some cases, intercontinental) tunnel-digging, ending up in places as varied as Mexico (Bully For Bugs, 1953), the Himalayas (The Abominable Snow Rabbit, 1960) and Antarctica (Frigid Hare, 1949) all because he "should'a taken that left toin at Albukoikee." He first utters that phrase in Herr Meets Hare (1945), when he emerges in the Black Forest, a cartoon seldom seen today due to its blatantly topical subject matter. When Goering says to Bugs, "There is no Las Vegas in 'Chermany'" and takes a potshot at Bugs, Bugs dives into his hole and says, "Joimany! Yipe!", as Bugs realizes he's behind enemy lines. The confused response to his "left toin" comment also followed a pattern. For example, when he tunnels into Scotland in 1948's My Bunny Lies Over The Sea, while thinking he's heading for the La Brea Tar Pits in Los Angeles, California, it provides another chance for an ethnic stereotype: "Therrre's no La Brrrea Tarrr Pits in Scotland!" (to which Bugs responds, "Uh...what's up, Mac-doc?"). A couple of late-1950s shorts of this ilk also featured Daffy Duck travelling with Bugs.Bugs Bunny has some similarities to figures from mythology and folklore, such as Br'er Rabbit, Nanabozho, or Anansi, and might be seen as a modern trickster (for example, he repeatedly uses cross-dressing mischievously). Unlike most cartoon characters, however, Bugs Bunny is rarely defeated in his own games of trickery. One exception to this is in the short Hare Brush in which Elmer Fudd ultimately carries the day at the endhowever critics note that in this short Elmer had become Bugs Bunny and Bugs had become Elmer, and it is only by becoming Bugs that Elmer can win.The name "Bugs" or "Bugsy" as a nickname means "crazy" (or "loopy").

16Blood TypesIA, IB, or iMultiple Alleles

IAIA or IAiIBIB or IBiIAIBiiWhen one trait is controlled by more than one gene.The genes may be on the same or different chromosomes.Both genes have a single phenotypic effect.Polygenic Traits

Polygenic inheritance, also known as quantitative or multifactorial inheritance refers to inheritance of a phenotypic characteristic (trait) that is attributable to two or more genes and their interaction with the environment. Unlike monogenic traits, polygenic traits do not follow patterns of Mendelian inheritance (qualitative traits). Instead, their phenotypes typically vary along a continuous gradient depicted by a bell curve.[1]An example of a polygenic trait is human skin color. Many genes factor into determining a person's natural skin color, so modifying only one of those genes changes the color only slightly. Many disorders with genetic components are polygenic, including autism, cancer, diabetes and numerous others. Most phenotypic characteristics are the result of the interaction of multiple genes.Examples of disease processes generally considered to be results of multifactorial etiology:Diabetes Mellitus[2] Cancer[2] Cleft palate[3] [2] Multifactorially inherited diseases are said to constitute the majority of all genetic disorders affecting humans which will result in hospitalization or special care of some kind[4] [5].

18Coat Color in Labrador RetrieversControlled by two different genes, the B gene and the E gene.A dihybrid cross of two black labs (BbEe x BbEe) results in:9 Black Pups3 Chocolate Pups3 Golden Pups1 Golden Pup with a brown nose and light eyes.Polygenic Traits

http://www.oakhillkennel.com/library/color.htmlColorThere are three recognized colors for Labs:[7] black (a solid black color), yellow (anything from light cream to gold to "fox-red"), and chocolate (medium to dark brown).Puppies of all colors can potentially occur in the same litter. Color is determined primarily by two genes. The first gene (the B locus) determines the density of the coat's pigment granules: dense granules result in a black coat, sparse ones give a chocolate coat. The second (E) locus determines whether the pigment is produced at all. A dog with the recessive e allele will produce little pigment and will be yellow regardless of its genotype at the B locus.[10] Variations in numerous other genes control the subtler details of the coat's coloration, which in yellow Labs varies from white to light gold to a fox red. Chocolate and black Labs' noses will match the coat color.

The Labrador is an exceptionally popular dog. For example as of 2006:Widely considered the most popular breed in the world.[42][43][3] Most popular dog by ownership in USA (since 1991),[44][45] UK,[46] Australia,[47] New Zealand[48] and Canada.[49] In both the UK and USA, there are well over twice as many Labradors registered as the next most popular breed.[44][46] If the comparison is limited to dog breeds of a similar size, then there are around 3 - 5 times as many Labradors registered in both countries as the next most popular breeds, the German Shepherd and Golden Retriever.[44][46] Most popular breed of assistance dog in the United States, Australia and many other countries, as well as being widely used by police and other official bodies for their detection and working abilities.[4] Approximately 6070% of all guide dogs in the United States are Labradors (see below).[28] Seven out of 13 of the Australian National Kennel Council "Outstanding Gundogs" Hall of Fame appointees are Labradors (list covers 2000-2005).[50]

19Eye ColorBrown GeneGreen GenePolygenic Traits

Eye color is an inherited trait influenced by more than one gene.[6][7] There are two major genes and other minor ones that account for the tremendous variation of human eye color.[8] In humans, three genes associated with eye color are currently known: EYCL1, EYCL2, and EYCL3.[9][10] These genes account for three phenotypic eye colors (brown, green, and blue) in humans.[3] Eye color usually stabilizes when an infant is around 6 months old.[11]In 2006, the molecular basis of the EYCL3 locus was resolved.[12] In a study of 3839 people, researchers reported that 74% of total variation in eye color was explained by a number of single nucleotide polymorphisms (SNPs) near the OCA2 gene (OMIM: 203200). OCA2 was previously known because, when mutated, the gene can result in a type of albinism. The recent study showed that different SNPs strongly associate with blue and green eyes as well as variations in freckling, mole counts, hair and skin tone. The authors speculate that the SNPs may be in an OCA2 regulatory sequence and thus influence the expression of the gene product, which in turn affects pigmentation.[13] A 2008 study demonstrated that a specific mutation within the HERC2 gene that regulates OCA2 expression is responsible for blue eyes[14] (see below).Blue eyes with brown spot, Green eyes and Gray eyes are caused by an entirely different part of the genome. As Eiberg said: "The SNP rs12913832 is found to be associated with the brown and blue eye color, but this single DNA variation cannot explain all the brown eye color variation from dark brown over hazel to blue eyes with brown spots".

"Behind Blue Eyes" is a song written by Pete Townshend of The Who for his Lifehouse project. It first appeared on The Who's 1971 Who's Next album, along with a number of other remnants from the project.The song is one of the most well-known of The Who's recordings. It starts off with a solo voice singing over a finger-picked guitar, later adds in bass guitar and ethereal harmonies, eventually breaks out into full-scale rock anthem when a second theme is introduced near the end, and wraps up by a brief reprise of the quieter first theme. Songs written in alternating sections were something of a trademark of Townshend's writing of the period, going back at least to Tommy, where it was used in "Christmas" and "Go to the Mirror!" The guitar riff at the end of the rock anthem section is also used after the bridge during the song Won't Get Fooled Again, perhaps serving as a link between the two songs when Who's Next was intended to be a rock opera. (Some musical themes from Tommy and Quadrophenia appear in multiple places.)The lyrics are a first-person lament from a man in the Lifehouse story, variously identified as 'Brick' or 'Jumbo', who is always angry and full of angst because of all the pressure and temptation that surrounds him, and the song was intended to be his "theme song" had the project been successful. (The lyrics of the rocking section near the end were actually written by Townshend as a prayer when he was a disciple of Meher Baba after being tempted by a groupie, and incorporated into the song when it was written.)The version of "Behind Blue Eyes" on the original Who's Next album was actually the second version the band recorded; the earlier version appears as a bonus track on the remastered CD release, which features Al Kooper on Hammond Organ.

20When traits are determined by several factors from the genetic makeup and the organisms environment.The genes only represent the potential.Environmental influences turn on the genes at different times and in different amounts.Multifactorial Traits

Generally, multifactorial traits outside of illness contribute to what we see as continuous characteristics in organisms, such as height[4], skin color, and body mass[6]. All of these phenotypes are complicated by a great deal of interplay between genes and environment[4]. While some authors[4] [6] include intelligence in the same vein, and it is tempting to do so, the problem with intelligence is that it is so ill-defined. Indeed, the entry on intelligence offers so many definitions, that the point is easily made that there is no single, agreed-upon entity that one could say amounts to a definable cluster of heritable traits.The continuous distribution of traits such as height and skin colour described above reflects the action of genes that do not quite show typical patterns of dominance and recessiveness. Instead the contributions of each involved locus are thought to be additive. Writers have distinguished this kind of inheritance as polygenic, or quantitative inheritance[7].Thus, due to the nature of polygenic traits, inheritance will not follow the same pattern as a simple monohybrid or dihybrid cross[5]. Polygenic inheritance can be explained as Mendelian inheritance at many loci[4], resulting in a trait which is normally-distributed. If n is the number of involved loci, then the coefficients of the binomial expansion of (a + b)2n will give the frequency of distribution of all n allele combinations. For a sufficiently high n, this binomial distribution will begin to resemble a normal distribution. From this viewpoint, a disease state will become apparent at one of the tails of the distribution, past some threshold value. Disease states of increasing severity will be expected the further one goes past the threshold and away from the mean[7].There are, however, many traits and disease states where many genes are involved, but their contribution is not equal, or additive.

21Temperature, nutrition, light, chemicals, and infections can influence gene expression.Arctic Foxes have coats that change color due to temperature.Multifactorial Traits

The Arctic fox has a circumpolar range, meaning that it is found throughout the entire Arctic, including the outer edges of Greenland, Russia, Canada, Alaska, and Svalbard, as well as in sub-Arctic and alpine areas, such as Iceland and mainland alpine Scandinavia. The conservation status of the species is good, except for the Scandinavian mainland population. It is acutely endangered there, despite decades of legal protection from hunting and persecution. The total population estimate in all of Norway, Sweden and Finland is a mere 120 adult individuals.The arctic fox is the only native land mammal to Iceland. It came to the isolated North Atlantic island at the end of the last ice age, walking over the frozen sea.The abundance of the Arctic fox species tends to fluctuate in a cycle along with the population of lemmings. Because the fox reproduces very quickly and often dies young, population levels are not seriously impacted by trapping. The Arctic fox has, nonetheless, been eradicated from many areas where humans are settled.The Arctic fox is losing ground to the larger red fox. Historically, the gray wolf has kept red fox numbers down, but as the wolf has been hunted to near extinction in much of its former range, the red fox population has grown larger, and it has taken over the niche of top predator. In areas of northern Europe there are programs in place that allow hunting of the red fox in the Arctic fox's previous range.As with many other game species, the best sources of historical and large scale population data are hunting bag records and questionnaires. There are several potential sources of error in such data collections (Garrott and Eberhardt 1987). In addition, numbers vary widely between years due to the large population fluctuations. However, the total population of Arctic foxes must be in the order of several hundred thousand animals (Tannerfeldt 1997).The world population is thus not endangered, but two Arctic fox subpopulations are. One is the subspecies Alopex lagopus semenovi on Mednyi Island (Commander Islands, Russia), which was reduced by some 85-90%, to around 90 animals, as a result of mange caused by an ear tick introduced by dogs in the 1970s (Goltsman et al. 1996). The population is currently under treatment with antiparasitic drugs, but the result is still uncertain.The other threatened population is the one in Fennoscandia (Norway, Sweden, Finland and Kola Peninsula). This population decreased drastically around the turn of the century as a result of extreme fur prices which caused severe hunting also during population lows (Lnnberg 1927, Zetterberg 1927). The population has remained at a low density for more than 90 years, with additional reductions during the last decade (Angerbjrn et al. 1995). The total population estimate for 1997 is around 60 adults in Sweden, 11 adults in Finland and 50 in Norway. From Kola, there are indications of a similar situation, suggesting a population of around 20 adults. The Fennoscandian population thus numbers a total of 140 breeding adults. Even after local lemming peaks, the Arctic fox population tends to collapse back to levels dangerously close to non-viability (Tannerfeldt 1997).

22

Height, Intelligence, Cholesterol, Weight, Mental Illness, etc.Multifactorial Traits

How do our chromosomes determine our sex?Sex Determination and Sex-linked TraitsSection 12.2Humans have a total of 46 chromosomes, or 23 pairs:22 pairs of autosomes1 pair of sex chromosomesAutosomesAll of the chromosomes that determine the traits other than sex.Come in different sizes with different genes on them.Pairs 1-22

Sex Determination

Sex ChromosomesDetermine the sex of the individual.Pair 23In females, these chromosomes match in the form of XX.In males, these chromosomes are different, as in XY.Sex Determination

The combination of sex chromosomes decides if you are a boy or a girl.A mother (XX) can only supply eggs that have an X chromosome.The father (XY) has some sperm with a X chromosome and some with a Y chromosome.Sex DeterminationXXXYXXXXXYXYG- 50% XX; 50% XYP- 50% female; 50% maleComparing the X and the Y

Other proposed genes on the Y chromosome:29Genes that are located on the sex chromosomes.The X chromosome contain many important genes that are necessary for survival.The Y chromosome contains the SRY gene which determines maleness.Sex-Linked Traits

Impact upon anatomical sexSince its discovery, the importance of the SRY gene in sex determination has been extensively documented:Humans with one Y chromosome and multiple X chromosomes (XXY, XXXY etc.) are usually males. Individuals with a male phenotype and an XX (female) genotype have been observed; these males have the SRY gene in one or both X chromosomes, moved there by chromosomal translocation. (However, these males are infertile.) Similarly, there are females with an XXY or XY genotype. These females have no SRY gene in their Y chromosome, or the SRY gene exists but is defective (mutated). SRY and the OlympicsOne of the most controversial uses of this discovery was as a means for gender verification at the Olympic Games, under a system implemented by the International Olympic Committee in 1992. Athletes with a SRY gene were not permitted to participate as females, although all athletes in whom this was "detected" at the 1996 Summer Olympics were ruled false positives and were not disqualified. In the late 1990s, a number of relevant professional societies in United States called for elimination of gender verification, including the American Medical Association, the American Academy of Pediatrics, the American College of Physicians, the American College of Obstetricians and Gynecologists, the Endocrine Society and the American Society of Human Genetics, stating that the method used was uncertain and ineffective.[2] The screening was eliminated as of the 2000 Summer Olympics.[2][3][4]SRY-related diseases and defectsIndividuals with XY genotype and functional SRY gene can have a female phenotype, where the underlying cause is androgen insensitivity syndrome (AIS).SRY has been linked to the fact that men are more likely than women to develop dopamine-related diseases such as schizophrenia and Parkinson's disease. SRY makes a protein that controls concentrations of dopamine, the neurotransmitter that carries signals from the brain that control movement and coordination.[5][6]30First observed in fruit flies (Drosophila).Fruit flies have either red or white eyes.Thomas Hunt Morgan noticed that all of the white-eyed flies were male.Therefore, eye-color in flies is a sex-linked trait.Sex-Linked Traits

31Because the X chromosome is much larger than the Y, most sex-linked traits are on the X.When writing the alleles for these traits, you must include the chromosomes that the individual has:Sex-Linked TraitsY Y Chromosome (no alleles)

XRX Chromosome(red-eyed allele)

XrX Chromosome(white-eyed allele)

Because males have only one X chromosome, they are more likely to get a single defective copy.XRY- red-eyed maleXrY- white-eyed maleSex-Linked Traits

XRY

XrY

Because females receive two X chromosomes, they are more likely to get a dominant allele that can cover the effects of the recessive trait.A carrier female has a recessive allele but does not show the trait (heterozygous)

Sex-Linked TraitsXRXRHomozygous Red-eyed Female

XRXrCarrier Female

XrXrWhite-eyed female (rare)Sex-Linked Punnett SquaresHomozygous Red-eyed Female x White-eyed MaleXRXRXrYXRXRXrYXRXrXRXrXRYXRYG- 50% XRXr 50% XRYP- 50% red-eyed female 50% red-eyed maleSex-Linked Punnett SquaresHeterozygous Red-eyed Female x Red-eyed MaleXRXrXRYXRXrXRYXRXRXRXrXRYXrYG- 25% XRXR 25% XRXr 25% XRY 25% XrYP- 50% red-eyed female 25% red-eyed male 25% white-eyed maleHow do pedigrees show inherited traits within families?Understanding PedigreesSection 12.1A graphic representation of traits inherited within a family.Allows scientists to trace the history of a genetic disorder.Uses symbols to represent individuals.Circles represent femalesSquares represent malesIf the symbol is shaded, the individual is affected by the trait.PedigreesNormal FemaleNormal MaleAffected FemaleAffected MaleInherited traits can be followed from generation to generation.Horizontal lines connect two individuals who have mated.Vertical lines represent the offspring of a union.PedigreesBbBbBbbbBBBbIII1212345Sex-Linked vs. AutosomalIf more males are affected by a trait than females, it is probably sex-linked.If it affects males and females equally, it is probably autosomal.Rules of Pedigrees

Dominant vs. RecessiveIf a trait skips a generation, it is recessive.If the trait is found in each generation, it is probably dominant.Rules of PedigreesIdentifying GenotypesIf any males are carriers, the trait is autosomal.If a male has a sex-linked trait, his mother was probably a carrier.Rules of Pedigrees

Affects males and females equally.Skips generations (appears in some generations but not in others).Males can be carriersAutosomal Recessive

Affects males and females equallyDoes not skip any generations.Autosomal Dominant

Affects males more than females.Skips generations.Must use the chromosomes (XY or XX)Sex-Linked Recessive

Example #1: Albinism

Are males affected more frequently that females?NOAutosomal DisorderDoes the disorder skip generations?YES (P1)Recessive DisorderAutosomal Recessive

A- normala - albinoAssign codes for the alleles.Code A for the dominant normal allele.Code a for the recessive allele for albinism.Affected individuals must be homozygous for a.First generation parents must be Aa because they have normal phenotypes, but affected offspring.Normal individuals must have at least one A.#1 must transmit a to each offspring.The A in the offspring must come from the father.Normal father could be either heterozygous or homozygous for an A.Both parents are heterozygous.Normal offspring could have received an A from either parent, or from both.Only the genotype of the offspring expressing albinism are known.Normal offspring must have received an a from their affected father.

46Example #2: Hemophilia

Are males affected more frequently that females?YESSex-Linked DisorderDoes the disorder skip generations?YES Recessive DisorderSex-Linked Recessive

+ = normalH = hemophilia

All females are XXAll males are XY.Assign codes for the alleles.Code H for the recessive hemophilia allele.Code + for the wild-type normal allele.Affected individuals must have an H on an X chromosome.All daughters of an affected father receive an X chromosome with the H allele.Normal individuals must have at least one X chromosome with the wild-type allele, +.

47Pedigree PracticeGenetic Trait: ACHOO(Sneezes in response to light)#1- Is this trait sex-linked or autosomal?#2- Is this trait dominant or recessive?#3- What is the genotype of individual A?#4- What is the genotype of individual B?#5- What is the genotype of individual C?ABCD#6- What is the genotype of individual D?48A picture of an individuals chromosomes.Homologous chromosomes are paired up.Pairs are arranged by size.Karyotypes can help diagnose chromosomal disorders.Karyotype

Six different characteristics of karyotypes are usually observed and compared: [4]differences in absolute sizes of chromosomes. Chromosomes can vary in absolute size by as much as twenty-fold between genera of the same family: Lotus tenuis and Vicia faba (legumes), both have six pairs of chromosomes (n=6) yet V. faba chromosomes are many times larger. This feature probably reflects different amounts of DNA duplication. differences in the position of centromeres. This is brought about by translocations. differences in relative size of chromosomes can only be caused by segmental interchange of unequal lengths. differences in basic number of chromosomes may occur due to successive unequal translocations which finally remove all the essential genetic material from a chromosome, permitting its loss without penalty to the organism (the dislocation hypothesis). Humans have one pair fewer chromosomes than the great apes, but the genes have been mostly translocated (added) to other chromosomes. differences in number and position of satellites, which (when they occur) are small bodies attached to a chromosome by a thin thread. differences in degree and distribution of heterochromatic regions. Heterochromatin stains darker than euchromatin, indicating tighter packing, and mainly consists of genetically inactive repetitive DNA sequences. A full account of a karyotype may therefore include the number, type, shape and banding of the chromosomes, as well as other cytogenetic information.Variation is often found:between the two sexes between the germ-line and soma (between gametes and the rest of the body) between members of a population (chromosome polymorphism) geographical variation between races mosaics or otherwise abnormal individuals. [5]

49When arranging the chromosomes:Autosomal Chromosomes are placed in order by size.The Sex Chromosomes are pair 23.Karyotypes

Number of chromosomes in a setA spectacular example of variability between closely related species is the muntjac, which was investigated by Kurt Benirschke and his colleague Doris Wurster. The diploid number of the Chinese muntjac, Muntiacus reevesi, was found to be 46, all telocentric. When they looked at the karyotype of the closely related Indian muntjac, Muntiacus muntjak, they were astonished to find it had female = 6, male = 7 chromosomes.[21]"They simply could not believe what they saw... They kept quiet for two or three years because they thought something was wrong with their tissue culture... But when they obtained a couple more specimens they confirmed [their findings]" [22] The number of chromosomes in the karyotype between (relatively) unrelated species is hugely variable. The low record is held by the nematode Parascaris univalens, where the haploid n = 1; the high record would be somewhere amongst the ferns, with the Adder's Tongue Fern Ophioglossum ahead with an average of 1262 chromosomes.[23] Top score for animals might be the common hermit crab Eupagurus at a mere 127 chromosomes.[24] The existence of supernumerary or B chromosomes means that chromosome number can vary even within one interbreeding population; and aneuploids are another example, though in this case they would not be regarded as normal members of the population.

50What to look for:The Sex Chromosomes:Male (XY) or Female (XX)Is there an odd number (XXY, XYY, XO, XXX)The AutosomesAre there two or three chromosomes for pair 21?Trisomy 21 Down SyndromeKaryotypes

Down syndrome or trisomy 21 (or Down's Syndrome in British English[1] and WHO ICD) is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British doctor who described the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy by Jrme Lejeune in 1959. The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance. Down syndrome can be identified during pregnancy or at birth.Individuals with Down syndrome tend to have a lower than average cognitive ability, often ranging from mild to moderate learning disabilities. A small number have severe to profound mental disability. The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although these statistics are heavily influenced by the age of the mother. Other factors may also play a role.Many of the common physical features of Down syndrome also appear in people with a standard set of chromosomes. They may include a single transverse palmar crease (a single instead of a double crease across one or both palms, also called the Simian crease), an almond shape to the eyes caused by an epicanthic fold of the eyelid, upslanting palpebral fissures, shorter limbs, poor muscle tone, a larger than normal space between the big and second toes, and protruding tongue. Health concerns for individuals with Down syndrome include a higher risk for congenital heart defects, gastroesophageal reflux disease, recurrent ear infections, obstructive sleep apnea, and thyroid dysfunctions.Early childhood intervention, screening for common problems, medical treatment where indicated, a conducive family environment, and vocational training can improve the overall development of children with Down syndrome. Although some of the physical genetic limitations of Down syndrome cannot be overcome, education and proper care will improve quality of life.[2]

51Example #1Number of Autosomes:

Number of Sex-Chromosomes:

Karyotype:

Phenotype:

44145 (X)Female-Turner SyndromeTurner syndrome or Ullrich-Turner syndrome encompasses several chromosomal conditions, of which monosomy X is the most common. It occurs in about 1 out of every 2500 female births.[1] Instead of the normal XX sex chromosomes for a female, only one X chromosome is present and fully functional; in rarer cases a second X chromosome is present but abnormal, while others with the condition have some cells with a second X and other cells without it (mosaicism). A normal female karyotype is labeled 46,XX; individuals with Turner syndrome are 45,X0. In Turner syndrome, female sexual characteristics are present but generally underdeveloped.

Common symptoms of Turner syndrome include:Short stature Lymphoedema (swelling) of the hands and feet Broad chest (shield chest) and widely-spaced nipples Low hairline Low-set ears Reproductive sterility Rudimentary ovaries Gonadal Streak (underdeveloped gonadal structures) Amenorrhea, or the absence of a menstrual period Increased weight, obesity Shield shaped thorax of heart Shortened metacarpal IV (of hand) Small fingernails Characteristic facial features Webbing of the neck (webbed neck) Coarctation of the aorta Poor Breast Development Horseshoe kidney Other symptoms may include a small lower jaw (micrognathia), cubitus valgus (turned-out elbows), soft upturned nails, palmar crease and drooping eyelids. Less common are pigmented moles, hearing loss, and a high-arch palate (narrow maxilla). Turner syndrome manifests itself differently in each female affected by the condition, and no two individuals will share the same symptoms.

52Example #2

Number of Autosomes:

Number of Sex-Chromosomes:

Karyotype:

Phenotype:

44347 (XYY)MaleJacobs SyndromeMost males have the 46-XY karyotype, but about 1 guy in 1000 has two Y chromosomes, and is an XYY ("diplo-Y", "diplo Y", "YY", "polysomy Y", "Jacob's syndrome"). If XYY men are at any greater "risk" of fathering XYY or XXY sons, the increase is small (Zygote 7: 131, 1999;