12.1 Section Objectives page 309 Interpret a pedigree. PATTERNS OF HEREDITY AND HUMAN GENETICS MENDELIAN INHERITANCE OF HUMAN TRAITS CHAPTER 12.1: Objectives Identify human genetic disorders caused by inherited recessive alleles. Predict how a human trait can be determined by a simple dominant allele. Section 12.1 Summary pages A _______ ____traces a family name and various family members through successive generations. Through a family tree, you can identify the relationships among your cousins, aunts, uncles, grandparents, and great- grandparents. Section 12.1 Summary pages A ________ is a graphic representation of genetic inheritance. It is a ________ made up of a set of symbols that identify ______ and _______, individuals affected by the trait being studied, and family relationships. Section 12.1 Summary pages Male Female Affected male Affected female Mating Parents Siblings Known heterozygotes for recessive allele Death Section 12.1 Summary pages In a pedigree, a _____ represents a ______; a ______ represents a ____. Female Male ? I II III IV Section 12.1 Summary pages Highlighted circles and squares represent individuals showing the ____ being studied. ? I II III IV Section 12.1 Summary pages Circles and squares that are ___highlighted designate individuals that do not show the trait. ? I II III IV Section 12.1 Summary pages A half-shaded circle or square represents a ________, a ___________ individual. ? I II III IV Section 12.1 Summary pages A _________ line connecting a ____ and a ______ indicates that the individuals are parents, and a _______ line connects parents with their offspring. Section 12.1 Summary pages Each horizontal row of circles and squares in a pedigree designates a __________with the most recent generation shown at the bottom ? I II III IV ? Section 12.1 Summary pages The generations are identified in sequence by _____ ________, and each individual is given an ______ number. I II III IV Section 12.1 Summary pages Most genetic disorders are caused by _____________ _______. _________ ______(__) is a fairly common genetic disorder among white Americans. Section 12.1 Summary pages Approximately one in 28 white Americans carries the recessive allele, and one in 2500 children born to white Americans inherits the disorder. Due to a defective _______ in the ______ ________, ______ ________ results in the formation and accumulation of thick mucus in the ______ and _________ tract. Section 12.1 Summary pages __________ (tay saks) disease is a recessive disorder of the central nervous system. In this disorder, a recessive allele results in the absence of an enzyme that normally breaks down a ______ produced and stored in tissues of the _______ ________ system. Section 12.1 Summary pages I II III IV Section 12.1 Summary pages _______________ (fen ul kee tun YOO ree uh), also called (____), is a recessive disorder that results from the absence of an enzyme that converts one amino acid, phenylalanine, to a different amino acid, _________. Because ____________ cannot be broken down, it and its by-products accumulate in the body and result in severe damage to the _______ ________ system. Section 12.1 Summary pages A ___ test is normally performed on all infants a few days after birth. Infants affected by PKU are given a diet that is low in ____________ until their ______ are fully developed. Ironically, the success of treating phenylketonuria infants has resulted in a new problem. If a female who is __________ _______ for PKU becomes pregnant, the high phenylalanine levels in her blood can damage her _____the developing baby. Section 12.1 Summary pages This problem occurs even if the fetus is _________ and would be ____________ normal. Section 12.1 Summary pages Phenylketonurics: Contains _______________ Section 12.1 Summary pages Remember that in Mendelian inheritance, a single _________ allele inherited from one parent is all that is needed for a person to show the dominant trait. Many _____ are inherited just as the rule of dominance predicts. Section 12.1 Summary pages A _____ ___, widows peak hairline, hitchhikers thumb, almond shaped eyes, thick lips, and the presence of hair on the middle section of your fingers all are examples of _______ traits. Section 12.1 Summary pages _____________ is a lethal genetic disorder caused by a rare dominant allele. It results in a breakdown of certain areas of the _____. Section 12.1 Summary pages Ordinarily, a dominant allele with such severe effects would result in _____ before the affected individual could have children and pass the allele on to the next generation. But because the onset of Huntingtons disease usually occurs between the ages of __ and __, an individual may already have had children before knowing whether he or she is affected. Section 12.1 Summary pages Typical Pedigree of Huntingtons Disease I 1 II III 12.2 Section Objectives page 315 Distinguish between alleles for incomplete dominance and codominance. WHEN HEREDITY FOLLOWS DIFFERENT RULES CHAPTER 12.2: Objectives 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 12.2 Summary pages Patterns of inheritance that are explained by Mendels experiments are often referred to as simple. However, many inheritance patterns are more ________ than those studied by Mendel. Section 12.2 Summary pages When inheritance follows a pattern of _________, _________ and _______ dominant individuals both have the same phenotype. When traits are inherited in an ________ __________pattern, however, the phenotype of heterozygous individuals is ___________ between those of the two homozygotes. Section 12.2 Summary pages For example, if a homozygous red-flowered snapdragon plant (__) is crossed with a homozygous white-flowered snapdragon plant (____), all of the F 1 offspring will have _____ ________. Section 12.2 Summary pages Red White All pink Red (RR) White (RR) Pink (RR) All pink flowers1 red: 2 pink: 1 white Section 12.2 Summary pages The new ________ occurs because the flowers contain enzymes that control pigment production. The R allele codes for an enzyme that produces a red pigment. The R allele codes for a _________ enzyme that makes no pigment. Section 12.2 Summary pages Because the heterozygote has only one copy of the R allele, its flowers appear pink because they produce only half the amount of red pigment that red homozygote flowers produce. Section 12.2 Summary pages ___________ _______cause the phenotypes of both homozygotes to be produced in heterozygous individuals. In ___________, both alleles are _________ equally. Section 12.2 Summary pages Although each _____ has only ___ alleles in the patterns of heredity you have studied thus far, it is common for more than two alleles to control a trait in a population. Traits controlled by more than two alleles have _________ ______. Section 12.2 Summary pages In humans the diploid number of chromosomes is__, or _______. There are __ pairs of homologous chromosomes called __________. Homologous autosomes look alike. The ___ ____of chromosomes differs in males and females. Section 12.2 Summary pages These two chromosomes, which determine the sex of an individual, are called ___ ______________ and are indicated by the letters __ and __. Section 12.2 Summary pages If you are ______, your 23 rd pair of chromosomes are homologous, __. If you are ____, your 23 rd pair of chromosomes ___, look different. X X Female YX Male Section 12.2 Summary pages Males usually have one __ and one __ chromosome and produce two kinds of _______, X and Y. Females usually have ___ X chromosomes and produce only X gametes. It is the male gamete that determines the ___ of the offspring. Section 12.2 Summary pages XX Female XY Male X X XY XX Female XY Male XX Female XY Male Section 12.2 Summary pages Traits controlled by genes located on sex chromosomes are called _______________. The alleles for sex-linked traits are written as _________ of the X or Y chromosomes. Because the X and Y chromosomes are not homologous, the Y chromosome has no _____________ allele to one on the X chromosome and no superscript is used. Section 12.2 Summary pages Also remember that any recessive allele on the X chromosome of a male will not be masked by a corresponding dominant allele on the Y chromosome. Section 12.2 Summary pages Females: Males: 1/2 red eyed 1/2 white eyed all red eyed White-eyed male (X r Y) Red- eyed female (X R X R ) F 1 All red eyed F2F2 Section 12.2 Summary pages The genes that govern sex-linked traits follow the inheritance pattern of the sex chromosome on which they are found. Section 12.2 Summary pages ___________ ____is the inheritance pattern of a trait that is controlled by two or more genes. The genes may be on the same chromosome or on different chromosomes, and each gene may have two or more alleles. __________ and _________ letters are used to represent the alleles. Section 12.2 Summary pages However, the allele represented by an uppercase letter is not dominant. All heterozygotes are intermediate in _________. In _________ inheritance, each allele represented by an uppercase letter contributes a small, but equal, portion to the trait being expressed. Section 12.2 Summary pages The result is that the phenotypes usually show a continuous range of variability from the ________ value of the trait to the ___________ value. Section 12.2 Summary pages The genetic makeup of an organism at __________ determines only the organisms potential to develop and function. As the organism develops, many ______ can influence how the gene is expressed, or even whether the gene is expressed at all. Two such influences are the organisms _________ and _________ environments. Section 12.2 Summary pages __________, nutrition, ______, chemicals, and __________ agents all can influence gene expression. Section 12.2 Summary pages In arctic foxes temperature has an effect on the expression of coat _____. Section 12.2 Summary pages External influences can also be seen in leaves. ______can have different sizes, __________, and shapes depending on the amount of light they receive. Section 12.2 Summary pages The internal environments of males and females are different because of _______ and structural differences. An organisms ___ can also affect gene function. 12.3 Section Objectives page 323 COMPLEX INHERITANCE OF HUMAN TRAITS CHAPTER 12.3: Objectives Identify codominance, multiple allelic, sex-linked and polygenic patterns of inheritance in humans. Distinguish among conditions that result from extra autosomal or sex chromosomes. Section 12.3 Summary pages Remember that in __________, the phenotypes of both homozygotes are produced in the heterozygote. One example of this in humans is a group of inherited red blood cell disorders called ______________________. Section 12.3 Summary pages In an individual who is _________ for the sickle-cell allele, the oxygen-carrying protein ____________ differs by one amino acid from normal hemoglobin. This defective hemoglobin forms crystal-like structures that change the shape of the red blood cells. _______ red blood cells are disc- shaped, but ________ red blood cells are shaped like a ______, or half-moon. Section 12.3 Summary pages The change in shape occurs in the bodys narrow ___________ after the hemoglobin delivers _______ to the cells. Normal red blood cell Sickle cell Section 12.3 Summary pages Abnormally shaped blood cells, _____ blood flow, _____ small vessels, and result in _____ damage and pain. Normal red blood cell Sickle cell Section 12.3 Summary pages Individuals who are heterozygous for the allele produce both normal and sickled hemoglobin, an example of ___________. Individuals who are _________ are said to have the sickle-cell trait because they can show some signs of sickle-cell-related disorders if the availability of _______ is reduced. Section 12.3 Summary pages Mendels laws of heredity also can be applied to traits that have more than two alleles. The ____ blood group is a classic example of a single gene that has multiple alleles in humans. Section 12.3 Summary pages Human Blood Types l A l A or l A li l B l B or l B i lA lBlA lB ii Genotypes Surface Molecules Phenotypes A B A and B None A B AB O Section 12.3 Summary pages Determining _____ type is necessary before a person can receive a blood ___________ because the red blood cells of incompatible blood types could ______ together, causing death. Section 12.3 Summary pages The gene for blood type, gene l, codes for a _______ that attaches to a _________ protein found on the surface of red blood cells. The __ and __ alleles each code for a different molecule. Your ______ system recognizes the red blood cells as belonging to you. If cells with a different _______ molecule enters your body, your immune system will attack them. Section 12.3 Summary pages The __ allele is dominant to __, so inheriting either the ___ alleles or the ____ alleles from both parents will give you ______blood. Surface molecule __ is produced. Surface molecule A Section 12.3 Summary pages The __ allele is also dominant to __. To have type __ blood, you must inherit the __ allele from one parent and either another __ allele or the __ allele from the other. Surface molecule __ is produced. Surface molecule B Section 12.3 Summary pages The __ and __ alleles are ____________. This means that if you inherit the __ allele from one parent and the __ allele from the other, your red blood cells will produce both surface molecules and you will have _____ ___blood. Surface molecule B Surface molecule A Section 12.3 Summary pages The __ allele is _________ and produces no surface molecules. Therefore, if you are homozygous __, your blood cells have __ surface molecules and you have blood ______. Section 12.3 Summary pages Many human traits are determined by genes that are carried on the sex chromosomes; most of these genes are located on the __chromosome. The pattern of _______________________ is explained by the fact that males, who are XY, pass an X chromosome to each daughter and a Y chromosome to each son. Section 12.3 Summary pages Females, who are XX, pass one of their X chromosomes to each child. Male Female SpermEggs Female Male FemaleMale Female EggsSperm Section 12.3 Summary pages If a son receives an __ chromosome with a recessive allele, the recessive ________ will be expressed because he does not inherit on the __ chromosome from his father a dominant allele that would ____ the expression of the recessive allele. Two traits that are governed by X-linked recessive inheritance in humans are ______________________and __________. Section 12.3 Summary pages People who have red- green color blindness cant differentiate these two colors. Color blindness is caused by the inheritance of a recessive allele at either of two gene sites on the __ chromosome. Section 12.3 Summary pages ______________is an X-linked disorder that causes a problem with blood clotting. About one ____ in every 10,000 has hemophilia, but only about one in 100 million _______ inherits the same disorder. Section 12.3 Summary pages Males inherit the allele for hemophilia on the __ chromosome from their carrier mothers. One recessive allele for __________ will cause the disorder in males. Females would need ___ __________ alleles to inherit hemophilia. Section 12.3 Summary pages Although many of your traits were inherited through simple Mendelian patterns or through multiple alleles, many other human traits are determined by polygenic inheritance. Section 12.3 Summary pages In the early 1900s, the idea that ________________occurs in humans was first tested using data collected on skin color. Scientists found that when light-skinned people mate with dark-skinned people, their offspring have ___________ skin colors. Section 12.3 Summary pages This graph shows the expected distribution of human skin color if controlled by one, three, or four genes. Number of Genes Involved in Skin Color Observed distribution of skin color Expected distribution- 1 gene Expected distribution- 4 genes Expected distribution- 3 genes Range of skin color Light Right Number of individuals Section 12.3 Summary pages What would happen if an entire chromosome or part of a chromosome were missing from the complete set? As you have learned, ___________ numbers of chromosomes in offspring usually, but not always, result from accidents of _______. Many abnormal ____________ effects result from such mistakes. Section 12.3 Summary pages Humans who have an extra whole or partial autosome are ________that is, they have three of a particular autosomal chromosome instead of just two. In other words, they have __ _________________. To identify an abnormal number of chromosomes, a sample of cells is obtained from an individual or from a fetus. Section 12.3 Summary pages __________ chromosomes are photographed; the chromosome pictures are then enlarged and arranged in pairs by a computer according to length and location of the ____________. Section 12.3 Summary pages This chart of chromosome pairs is called a ___________, and it is valuable in identifying unusual chromosome numbers in cells. Section 12.3 Summary pages ____ _________is the only autosomal _______ in which affected individuals survive to adulthood. It occurs in about one in 700 live births. Section 12.3 Summary pages Down syndrome is a group of symptoms that results from trisomy of ____________ __. Individuals who have Down syndrome have at least some _______ of mental retardation. The incidence of Down syndrome births is higher in _____ mothers, especially those over 40. Section 12.3 Summary pages Many abnormalities in the number of sex chromosomes are known to exist. An X chromosome may be missing (designated as __) or there may be an extra one (___ or ____). There may also be an extra Y chromosome (____). Any individual with at least one Y chromosome is a ____, and any individual without a Y chromosome is a _______. Most of these individuals lead normal lives, but they ______ have children and some have varying degrees of mental retardation.