Chapter 12 Inheritance Patterns and Human Genetics

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DESCRIPTION Chapter 12 Inheritance Patterns and Human Genetics. Objectives. Tell the difference between sex chromosomes and autosomes Define different types of mutations Evaluate and create pedigree charts. I. Chromosomes. - PowerPoint PPT Presentation


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Chapter 12 Inheritance Patterns and Human Genetics

ObjectivesTell the difference between sex chromosomes and autosomesDefine different types of mutationsEvaluate and create pedigree chartsI. ChromosomesIn the early 1990s a researchers noticed that Drosophilia melanogaster (fruit flies) had 4 chromosomes3 were the same in both males and females and 1 was different

exploratorium.eduIn the early 1990s researchers were studying chromosomes in Drosophila melanogaster when they noticed that one pair differed in size and shape. In females the 4 pairs were of identical size and shape while in males one chromosome was shorter than the other one. Today we call them x and y chromosomes. Two Xs is a girl and an X,Y is male.32 Types of ChromosomesSex chromosomes contain genes that determine the sex of an individual (X or Y)Males decide the genderAutosomes-all the other chromosomes that are not involved in gender determinationCause about half of all genetic diseasesWe know that in humans girls have 2 X chromosomes and boys have an X and a Y. In other animals like chickens the males have two identical sex chromosomes while the females are the ones who have two different ones. Plants lack sex chromosomes entirely because they are asexual having both male and female parts.Sperm have a 50/50 chance of giving an X or a Y chromosome while eggs only have an X, making that the only thing they can pass on.4

II. Linked TraitsPair of genes that are inherited togetherThey are located in the same chromosome and very close together.graphicshunt.comCrossing over is the exchange of pieces of DNA between homologous chromosomes.5Sex-linked Genes and TraitsRefers to a trait that is coded for by an allele on a sex chromosome (X or Y)More X-linked traits than Y-linked traits because the of the size differenceMales who have an X chromosome that carries a recessive allele will exhibit the sex-linked trait Females have less of a chance expressing an X linked disease because they have 2 X-chromosomes

karakalpak.comFemales have less of a chance expressing the trait because if they get a dominant trait and a recessive trait only the dominate trait will show. However, if the female has a son she has a 50% chance of passing along the recessive trait to him. Females can never get a Y-linked disease. Why do you think this is?6MutationsGerm-cell occur in the gametesEffect the offspringSomatic-cell occur in an organisms body cellsCan not be inherited-results in things like leukemia or skin cancerLethal cause death, often before birthBeneficial help the organism survive and reproduce

photography.nationalgeographic.comWhat is a mutation? Change in the nucleotide sequence of DNAGerm cell dont normally affect the individual carrying it but will be passed on to the next generationSomatic cell- a person who spends to much time suntanning might develop a mutation in a skin cell. Lethal implies that the individual will not live long it could be months or years depending on the mutation. It can inhibit the individual from being able to perform vital functions. An example is Turners syndrome- the individual survives but is infertile so in a sense its lethal because their genes can not be passed on.Beneficial- pandas appear to have 5 thumbs but their thumb is actually an extension of a wrist bone. This helps them keep their grip on bamboo and gives an anvantage over other pandas who dont have this mutationPenguins have flightless wings and small legs not the greatest on land but masters of the water7Chromosome MutationsChange the structure of the chromosomeDeletion and InsertionLoss of nucleotide bases or an addition of them

biology-online.orgAn example of an insertion is Huntingtons disease, the codon CAG is normally repeated 10-28 times within your DNA but in people who have this it is repeated 36-120 times. Normally starts when you are an adult and it is a degenerative disease in which parts of your brain waste away8InversionTranslocationA piece of the chromosome breaks off and flips around backward A piece of one chromosome breaks off and attaches to a nonhomologous chromosome

staff.jccc.net chromosomes occur in pairsNonhomologous chromosomes are different9NondisjunctionThe chromosomes dont separate during meiosis so one gamete receives 2 copies and the other receives none.

2 Types of Nondisjunction Trisomy an extra chromosome in every cellMost of these disorders make it very difficult for the individual to survive Trisomy 21-down syndromeTrisomy 18 &13-normally die before age 1Monosomy absence of 1 chromosomeTypically lethal to embryonic developmentTurners syndrome

cdadc.comTrisomy is named after the chrosome which is tripled examples include Trisomy 18 & 13 have severe mental retardation and health problems involving almost every organ. Trisomy 22 is the most common cause for miscarriage. Trisomy 13 is Patau syndrome mental retaredation, eyes may fuse together, heart defectsTurners syndrome- affects the development of girls, they are normally short and their ovaries dont work properly making them infertile11Gene MutationsPoint mutation change within a single geneSubstitution one nucleotide replaces anotherFrameshift mutation if some nucleotides are deleted the entire segment of DNA moves down changing the codons for amino acidsDetrimental to the proteins functionInsertion mutation one or more nucleotides are added which can result in a frameshift mutation

A frame shift mutation occurs when a deletion or substitution appear in a part of the DNA that codes for an amino acid 12Example of SubstitutionSickle Cell Anemia: only 1 amino acid is substituted to produce the sickle shapeRecessive trait that prohibits Hemoglobin from binding correctlyTo the red blood cell

unitedhealthdirectory.comFrameshift MutationChanging one letter completely alters the codon sequence of gene mutationsSubstitution:Original the fat cat ate the wee rat.Mutation - The fathat ate the wee rat.Insertion:Original: The fat cat ate the wee rat.Mutation: The fat cat xlw ate the wee rat.Frameshift:Original: The fat cat ate the wee rat.Mutation: The fat caa tet hew eer at.

1. Below is the base sequece for the normal protein for normal hemoglobin and sickle cell:Normal: GGG CTT CTT TTT Sickle: GGG CAT CTT TTTIs this a point or frameshift mutation? Explain.2. Delete the first H in the following sequence and regroup the letters in groups of three. Does the sentence still make sense? What type of mutation is thisTHE FAT CAT ATE THE RAT3. Name 2 chromosome mutations. How are they alike? How are they different?4. Using the sequence ATT GCA AAG GGT. Give an example of a deletion, insertion, and substitution. Circle the change you have made.5. What is the difference between sex chromosomes and autosomes?

16List of Genetic Disorders Pick 1 for your projectHuntingtons DiseaseDowns SyndromeCystic FibrosisDuchenne muscular dystrophySickle Cell AnemiaTrisomy 18 (Edwards)Tay-Sachs diseaseColor blindnessPKU (Phenylketonuria) Fragile X syndrome

ThalassemiaMarfan syndromeBreast CancerHemophiliaCri du ChatPolydactylyMaple Syrup urine diseaseTurner SyndromeKlinefelter's syndrome, (XXY syndrome)Super males (XYY)Patau syndromeAlbinismII. PedigreesDiagram that shows how a trait is inherited over several generations

A circle represents a femaleA square represents a male If the circle or square is filled in that means the individual has the trait Horizontal lines indicate marriage or having children Vertical lines show offspringReading Pedigrees

Is the mom or dad in generation I affected by a trait?How many offspring are shown in generation II?How many daughters & sons in generation II?How many have the trait?How many offspring does daughter #1 have? How many have the trait?Practice ProblemsPatterns of InheritanceAutosomal Dominant TraitsPassed on to sons or daughters even if only one parent has the geneAffected individuals who mate with an unaffected individual have a 50% chance of passing on the gene as long as they are not homozygous for the traitCan appear in males and females equallyWhat must the genotype of the parents be to produce a child #7 who is unaffected?What is the genotype of #9?What are the genotypes of the 3 children in the third generation?

#7 = heterozygous#9 heterzygousThird generation homozygous recessive22Recessive PedigreesIn order to be passed on both parents must have the geneTraits can be passed on if both parents are carriers of the traitHave the trait but it isnt expressed because they also have the dominant traitAn individual who is infected may have parents who are notIf both parents are affected, all of their children will be affected

Carriers for Autosomal recessive traits

We know this trait is recessive because neither parent expresses it but they have a child who has it. This makes them both carries of the allele because they both passed the recessive allele down. The other child got at least one of the dominant alleles from the parents but we cant tell whether he is homozygous dominant for the trait or recessive.24 Recessive Pedigree

If individuals 2 + 3 in generation 3 have more children- will they be affected?Can Individual #8 in gen. 3 have any unaffected children?Can individual #9 in gen 3 have affected children?All children of individuals 2 and 3 will be affected#8 can only have unaffected children if they mate with someone who has a dominant allele#9 yes because we cant tell if they are homozygous for the trait or a carrier25Sex Linked TraitsLocated only the sex chromosomes (X and Y)More frequently expressed on males than femalesY-linked is male only X-linked passed from mother to sonMainly expressed in malesDaughters are carriersX-linked TraitsTraits that are on the X chromosomeMales are affected more than femalesColor blindness is an X-linked recessive disorder passed from mother to son

Color blindness is an x-linked recessive disorder, women carry the gene but do not express it because they have 2 copies of the X chromosome. Pass it on to their sons because they get only 1 X chromosome. normal vision see this as 29, red/green see it as a 70.Those with normal vision will see this as a 5 and those who are color blind will read it incorrectly or not at allNormal is 15 color blindness is 17

27X-linked recessiveEvident in males because they only have 1 X chromosomeWomen are rarely affected because they have 2 X chromosomes-better chance of not getting itIf the father has the mutated gene all of his daughters will have it

If males get the mutant gene then they will have the trait. Girls will be carriers unless the mother is a carrier and the father has the diseaseExample is duschenne muscular distrophy28X-linked Dominant No transmission from father to sonAll daughters of the affected male will have itOnly 1 dominant allele is needed for the trait to be expressedWhat is the genotype of #2 in generation II?

Genetic DisordersDiseases that have a genetic basisResearchers have found that most traits are Polygenic influenced by several genesSkin color combination of 3-6 genes which control the amount of melanin in the skin

Complex characters influenced by both genes and environmentHeight, certain diseases such as breast cancer

cosbiology.pbworks.comBreast cancer can run in families, but environmental factors include a diet high in saturated fat30Incomplete Dominance Displaying a trait that is intermediate of the two parentsWavy hair comes from one parent having straight hair and one parent having curly hairRed flower and a white flower produce a pink flower

doctortee.comSex Influenced TraitMales and females can show different phenotypes even when they share the same genotypeEx: Male pattern baldness the allele is dominant in males but recessive in females due to the higher testosterone levels in malesSingle-Allele TraitsTrait controlled by 1 allele-dominant or recessive

Dominant ExamplesHuntingtons Disease- degradation of the brainPolydactly- presence of a sixth digitAchondroplastic dwarfism-dwarf size Recessive ExamplesCystic Fibrosis-most common lethal diseaseSickle-cell anemia-blood disorder Albinism- lack of color pigment in skin, hair, and eyes33Detecting Genetic diseaseAmniocentesis technique used to detect genetic disorders in a fetusChrionic villi sampling takes some cells derived from the placenta

Treatments depend on the specific disease

The do this by removing some of the amniotic fluid from the sac that surrounds the fetus between the 14th and 16th week of pregnancy. This allows them to look at the chromosomes and proteins in the fluid. Carries a slight risk of miscarriage.Sample taken between the 8th -10th week34


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