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Name_____________________________Per____ Genetics Problems Notes PreAP Biology Genetics and Predictions for Autosomal Traits Monohybrid Crosses: Predictions for one trait – in all probability Probability – the likelihood of an event - can be expressed as __fractions_ (1/2), ___percents__ (50%), or ratios_ (1:1) - geneticists use a _Punnett square_ to predict the possible outcomes of a cross (give the probability of a genotype or phenotype) - studying one trait at a time is called a __monohybrid_ cross - crosses are represented as: genotype x genotype ex) Yy x Yy or (less often) phenotype x phenotype ex) heterozygous yellow x heterozygous yellow Sample monohybrid cross problem. Use a punnett square to predict the results of a cross between two heterozygous yellow pea plants. Give the parent genotypes, the punnett square, the genotypic ratio, and the phenotypic ratio. Parent genotypes: ___Yy________x_____Yy________ Punnett square: Possible gametes from the other parent Numbers in the ratio must add up to the number of boxes in the Punnett square Y y Y YY Yy y Yy yy Genoptypic ratio: __1:2:1__ Phenotypic ratio: __3:1____ Remember, these are diploid organisms Possible gametes from one parent Each box in the Punnett square represents a possible zygote Always written homozygous dominant: heterozygous: homozygous recessive Always written dominant: recessive in simple Mendelian problems If you are asked for the percentage, or a fraction, or a ratio be sure you express your answer in that form. For example, if the problem asked “What percentage of the offspring would be green” your answer would be 25% (if you said ¼ or 0.25, or 3:1, your answer would be wrong because that is not what you were asked). If you are asked for a fraction, be sure you give a fraction, not a decimal, or a ratio, or a percent. 1 Practice Problems Monohybrid Crosses a. b. c. d. State the P generation Set up the punnett square Genotype and ratio Phenotype and ratio Y= yellow y= green 1. Cross a homozygous yellow plant with a green plant. a. _______ x _______ b. c. d. 2. Take two F1 generations from #1 and cross them. a. b. ______ x ______ c. d. 2 Name________________________ Per____ Genetics Problems II (Homework due ______________) A. List the correct alleles for the traits for each. Given: Black fur (B) is dominant over white fur (b) in rabbits. Normal skin (N) is dominant over albinism (n) in humans. 1. _____ heterozygous black fur 2. _____ homozygous normal skin 3. _____ heterozygous normal skin 4. _____ homozygous white fur 5. _____ homozygous albinism 6. _____ homozygous black fur B. Monohybrid Crosses: Use the symbols above to complete the following problems. 7. Cross a heterozygous normal skin man with a homozygous albino woman. What are the genotypes of the mom and dad? _____ x _____ Show your work with a Punnett square: What are the genotypes of the offspring? _____________ What’s the ratio or percentage of each?____________ What are the phenotypes of the offspring? _____________ What’s the ratio or percentage of each? ____________ 8. Cross a homozygous black rabbit with a homozygous white rabbit. What are the genotypes of the mom and dad rabbits? _____ x _____ Show your work with a Punnett square: What are the genotypes of the offspring? _____________ What’s the ratio or percentage of each?____________ What are the phenotypes of the offspring? _____________ What’s the ratio or percentage of each? ____________ 3 (Homework continued) 9. Cross a heterozygous normal skin man with a heterozygous normal skin female. What are the genotypes of the mom and dad ? _____ x _____ Show your work with a Punnett square: What are the genotypes of the offspring? _____________ What’s the ratio or percentage of each?____________ What are the phenotypes of the offspring? _____________ What’s the ratio or percentage of each? ____________ C. Use your own symbols for the following crosses. 10. Cross a heterozygous red flower with a homozygous recessive white flower. The letter for red is _____. The letter for white is _____. The genotypes of the parent flowers are _____ x _____ Show your work in a Punnett square: What are the genotypes of the offspring? _____________ What’s the ratio or percentage of each? ______________ What are the phenotypes of the offspring? _____________ What’s the ratio or percentage of each? ______________ 11. Cross a homozygous wire hair (dominant) dog with a homozygous recessive smooth hair texture dog. The letter for wire hair is _____. The letter for smooth is _____. The genotypes of the parent dogs are _____ x _____ Show your work in a Punnett square: What are the genotypes of the offspring? _____________ What’s the ratio or percentage of each? ______________ What are the phenotypes of the offspring? _____________ What’s the ratio or percentage of each? ______________ 4 Test cross – seeing the invisible Scientists wanted to know how to tell if an organism showing the dominant phenotype was homozygous or heterozygous so they developed the test cross. A test cross involves breeding (crossing) an organism whose genotype is recessive with a phenotypically dominant organism. Perform the following test crosses: a) YY x yy Genotypic ratio: ______________ Phenotypic ratio: _____________ b) Yy x yy Genotypic ratio: ______________ Phenotypic ratio: _____________ What is the difference in the results of the two test crosses? __________________________ Difficult Predictions—Intermediate Inheritance, Multiple Alleles, and Pleiotropy Intermediate inheritance – genes in between Mendel was lucky in the traits that he chose. One was always completely dominant and one completely recessive. In nature, this is rare. In intermediate inheritance the heterozygous offspring have a trait that is not exactly like the trait of either purebred parent. There are three forms of intermediate inheritance: incomplete dominance, codominance and polygenic inheritance. 1. Incomplete dominance - heterozygous offspring show a phenotype that is in between the phenotypes of the two homozygous parents. Neither allele is fully expressed*. Example: red snapdragons x white snapdragons produce pink snap dragons Pink snapdragons x pink snapdragons produce red, white and pink snapdragons Alleles can be indicated in several ways—just stick to one way for each problem. Capital and lowercase: Ex. RR = red, Rr = pink, rr = white Two different letters: Ex. RR = red, RW = pink, WW = white Capital letter and Capital letter with prime: Ex. RR = red, RR’ = pink, R’R’ = white Example: Palomino horses have blonde hair with white manes and tails; result from a cross between a chestnut horse and a white horse Example: hypercholesterolemia – normal genotype is HH and cholesterol levels are normal - Hh – cholesterol levels are twice as high - hh – cholesterol levels are 5x’s as high * in incomplete dominance, there is only one allele coding for the protein; therefore, less functional protein is produced, but enough that the phenotype is neither dominant nor recessive 5 Incomplete dominance: RR = Red RR’ = pink R’R’ = white a.= P generation b.=punnett square c.=genotypes & ratios d.=phenotypes & ratios Cross a pink Japanese four o’clock flower with a pink Japanese four o’clock. a. _____ x _____ c. b. d. 2. Codominance – both alleles express themselves __fully____. An example is human __blood ____ __types_____. Human blood types also show more than one allele, called __multiple_____ __alleles. The three alleles are _IA__, __IB__, and __i__. So in addition to codominance, human blood type also involves multiple alleles. Blood Type (phenotype) A B AB O Genotype (s) Can Donate to Can Receive from Cross someone with type AB blood with someone who is heterozygous for type A. a. b. _____ x _____ c. d. Another example includes roan horses. Roan horses have red hairs and white hairs and are born from a red horse crossed with a white horse. Most of the time, two different letters are used to represent the alleles. Ex. RR = red, RW = roan, WW = white 3. Polygenic Inheritance A trait controlled by two or more genes is called polygenic. Eye color and skin color are both examples in humans. Multiple alleles and pleiotropy – many alleles and traits Multiple alleles - (see human blood types) When a single gene affects more than one trait, the pattern of inheritance is called pleiotropy. An example is sickle cell anemia. People with two copies of the sickle cell gene have multiple effects (called pleiotropy) such as weakness, anemia, brain damage, spleen damage, and heart damage due to damage to the circulatory system resulting from the shape of the sickled red blood cells. 6 Intermediate Inheritance Crosses WS Incomplete Dominance: Name________________________ Per____ (Homework due _____________) Definition:____________________________________________________ Use the following for problems 1 and 2: RR’ = pink (RR=red and R’R’=white) 1. Cross a red and a white flower. What are the genotypes of the parent flowers? _____ x _____ Show your work with a Punnett square: Offspring genotypes? _____________ Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ 2. Cross two pink flowers. What are the genotypes of the parent flowers? _____ x _____ Show your work with a Punnett square: Offspring genotypes? _____________ Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ Codominance: Definition: ___________________________________________________ For codominance genotypes, it is appropriate to use any of the following ways to represent your alleles: Ex. Roan horses=both red hairs & white hairs (Red parent & white parent) RW = roan (RR=red and WW=white). Ex. Sickle Cell Anemia: abnormally shaped blood cells Use: AA=normal; SS = sickle shaped, so AS = normal and sickle for heterozygotes. 3. Cross 2 Roan horses. What are the genotypes of the parent horses? _____ x _____ Show your work with a Punnett square: Offspring genotypes? _____________ Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ 4. Cross a person with normal red blood cells with a sickle celled person. What are the genotypes of the parents? _____ x _____ Offspring genotypes? _____________ Show your work with a Punnett square: Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ 7 (Homework continued) 5. Cross two people who are heterozygous for normal & sickle blood cells. What are the genotypes of the parents? _____ x _____ Offspring genotypes? _____________ Show your work with a Punnett square: Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ Codominance & Multiple Alleles Definition (multiple alleles) ________________________________________ _____________________________________________________________ Human blood type is an example of a trait that is determined by multiple alleles and also illustrates codominance. Remember that there are 4 phenotypes for blood type: A, B, AB, and O. There is one genotype for type AB, it is IAIB. There is one genotype for type O, it is ii. There are two each for types A and B. Homozygous type A is IAIA; heterozygous type A is IAi. Homozygous B = IBIB; Heterozygous B = IBi. 6. Cross a person who is heterozygous for B and a person with type O . What are the genotypes of the parents? _____ x _____ Offspring genotypes? _____________ Show your work with a Punnett square: Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ 7. Cross a person who is type AB with a person who is homozygous for type A. What are the genotypes of the parents? _____ x _____ Show your work with a Punnett square: Offspring genotypes? _____________ Ratio or percent of each?____________ Offspring phenotypes? _____________ Ratio or percentage of each? ____________ 8 Name___________________________ Per____ Blood Type Baby Mystery--“Using Genetics to Help Solve Mysteries” Adapted from a worksheet by Merrill Publishing Co., 1991 (Homework due _____________) Geneticists are often called upon to solve mysteries using some of the tools you have become familiar with in this chapter. Using genetic clues, give a possible solution for each problem below. Problem: Four newborn babies in the delivery room of the hospital at the same time were mixed up by the person who typed the wristbands. The blood types of the four babies were known to be AB, O, A, and B. How did the doctors eventually find out which baby belongs to which set of parents? Given: Parents #1 had blood types O and AB Parents #2 had blood types AB and B Parents #3 both had blood type O Parents #4 had blood types O and A Use Punnett squares to determine the possible genotypes of the offspring. Parents # 1 Parents # 2 Homo B Parents # 2 Hetero B Parents # 3 Parents # 4 Homo A Parents # 4 Hetero A Possible Blood Types for Babies 1. Parents # 1 ______________________________________ 2. Parents # 2 ______________________________________ 3. Parents # 3 ______________________________________ 4. Parents # 4 ______________________________________ Conclusion: A. Baby with type AB blood belongs to Parents # _____. B. Baby with type B blood belongs to Parents # _____. C. Baby with type A blood belongs to Parents # _____. D. Baby with type O blood belongs to Parents # _____. 9 10 Dihybrid cross – cross involving two traits - the same theory and procedure is involved, but the number of possible gametes and the number of possible zygotes has increased - Example: Cross two plants heterozygous for round, yellow peas. Give the parent genotype, the Punnett square, and the phenotypic ratio Each parent has two copies of each gene and gives one copy of each gene to a gamete (diploid to haploid) Parent genotype: RrYy x RrYy Punnett square: Gametes from the second parent RY RY *RRYY Ry *RRYy RRyy *RrYy Rryy *RrYY *RrYy *RrYy Rryy rrYY @ rrYy @ rrYy @ rryy & rY ry Ry *RRYy rY ry *RrYY *RrYy Note that the ratio is always dominant dominant: dominant recessive: Phenotypic ratio: 9:3:3:1 recessive dominant: recessive recessive *:__:@:& Note that 1/16 of the offspring in a dihybrid cross are homozygous recessive, while 9/16 show the dominant phenotypes. Cross a heterozygous tall red plant with a homozygous tall, heterozygous red plant. T = tall R = red t = short r = white a. b. __TtRr__ x ___TTRr___ c. not necessary to do d. 11 Cross a heterozygous free large ear lobed boy with a heterozygous free large ear lobed girl. E = free hanging ear lobed L = large ear lobe e = attached ear lobe l = small ear lobe a. b. __________ x __________ c. not necessary to do d. 12 Dihybrid Crosses WS Name________________________ Per____ (Homework due ____________) Complete each question by answering the following information: A. the P1 generation genotypes C. the genotype and ratio (don’t do) B. the punnett square D. the phenotype & ratio In mice, the ability to run normally is a dominant trait. Mice with this trait are called running mice (R). The recessive trait causes mice to run in circles only. Mice with this trait are called waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over brown hair (b). 1. Cross a heterozygous running, heterozygous black mouse with a homozygous running, homozygous black mouse. A. _______ x ________ B. C. not necessary to do D. 2. Cross a heterozygous running, heterozygous black mouse with a heterozygous running, heterozygous black mouse. A. _______ x ________ B. C. not necessary to do D. 13 (Homework continued) Complete each question by answering the following information: A. the P1 generation genotypes, B. the punnett square, C & D answer the questions. Remember that there are 4 phenotypes for blood type: A, B, AB, and O. There is one genotype for type AB, it is AB. There is one genotype for type O, it is OO. There are two each for types A and B. Homozygous for Type A is AA, while the heterozygous is AO. For Type B, the homozygous is BB, and the heterozygous is BO. Blood types often include what is called the Rh Factor. Use P for positive and p for negative because, for these purposes, positive is dominant over negative 3. Cross a man with blood type AB+ (assume he is heterozygous for the Rh Factor) with a female with blood type type O+ (also heterozygous for the Rh Factor) A. _PpAB _ x _PpOO__ C. What are the possible blood types of B. the offspring? (ie B+, B-, A+, A-, O+, O-, AB+, AB-) D. What are the chances that an offspring of theirs will have a negative blood type? (express in ____ out of16). What are the chances that an offspring will be A+ (express in ____ out of 16? 4. Cross a female with blood type A- (heterozygous A) with a male who is homozygous blood type B+ (homozygous B and heterozygous +) A. ________ x _________ B. C. How many offspring will be blood type AB? (express in ____ out of16). D. What are the chances that an offspring of theirs will have a positive blood type? (express in ___ out of16). 14 Sex-linked traits Traits that are sex-linked are transmitted by genes located on the X or Y chromosome. In this class, we will just be studying traits that are sex-linked on the X chromosome, sometimes called X-linked. Carriers—individuals who are heterozygous for an inherited disorder but do not show symptoms. Carriers can pass the allele to their offspring. Examples include: Hemophilia (H=normal, h=affected); colorblindness (C=normal; c=affected); Duchenne muscular dystrophy (D=normal, d=affected) Ex. Hemophilia: H=normal, h=affected along with XX or XY Female Genotypes Male Genotypes Female Phenotypes Male Phenotypes XHXH NORMAL XHY NORMAL XHXh CARRIER (BUT NORMAL) AFFECTED XhY AFFECTED XhXh Why are more males than females affected by sex-linked disorders? __________________________________________________________________________ Can a male be a carrier for a sex-linked disorder? _______ Cross a female carrier with a male hemophiliac. a.= P generation b.=punnett square c.=genotypes & ratios d.=phenotypes & ratios a. b. _____ x _____ c. d. Who does a female child have to inherit hemophilia from? Who does a male child have to inherit hemophilia from? 15 Name________________________ Per___ Sex-linked Disorder Homework Problems (HW due_______________) In fruit flies, white eyes (r) is a sex-linked trait occurring only on the X chromosome (Red (R) is dominant). 1. If a white-eyed female(XrXr) is crossed with a red-eyed (wild type) male (XRY), predict the following: A. ____________ X ___________ (parental genotypes) B. Punnett square C. Possible genotypes: ________________________ Genotypic ratio: _______________________ D. Possible phenotypes: ______________________ Phenotypic ratio: ______________________ 2. Cross a white-eyed male with a homozygous wild-type female. A. ____________ X ___________ (parental genotypes) B. Punnett square C. Possible genotypes: ________________________ Genotypic ratio: _______________________ D. Possible phenotypes: ______________________ Phenotypic ratio: ______________________ 3. Lesch-Nyhan syndrome is an X-linked recessive disorder in which an enzyme deficiency results in a buildup of uric acid in the body. Work the following: A husband and wife, neither of whom have LeschNyhan syndrome, have a boy with the syndrome. What was the probability of having a child with Lesch-Nyhan syndrome for this couple? ______________ Show your work in the space below. A. ____________ X ___________ (parental genotypes) B. Punnett square C. Possible genotypes: ________________________ Genotypic ratio: _______________________ D. Possible phenotypes: ______________________ Phenotypic ratio: ______________________ 4. Their daughter does not have the syndrome. What is the probability that their daughter is a carrier (careful!)? ____________________ 5. If the couple has a 3rd child, what is the probability that it will NOT have Lesch-Nyhan syndrome? _________________ 16 Predictions and People Pedigree studies – all in the family People reproduce slowly and have few offspring. Therefore, geneticists use a pedigree a chart that shows how a trait and the genes that control it are inherited within a family over several generations, much like a family tree for specific traits. Pedigrees show phenotypes, but can often determine genotypes as well. Pedigrees can be used for other organisms, too. In a pedigree, an individual whose genes have a recessive trait but expresses the dominant trait is called a carrier. Benefits of Pedigrees: Help predict if a family member is a carrier of a disorder or trait. If a disorder is likely to be passed down, a genetic counselor can be consulted. A genetic counselor can assess the risk of passing on disease alleles. Genetic counseling Involves seeking advice from a doctor about the probability of passing a genetic disorder on to your children. A pedigree is developed, showing the probability of one or both parents carrying certain alleles. The probability that the disorder will occur in the offspring can then be determined. The couple can then evaluate the options Molecular tests on the mother, such as for Downs syndrome prior to birth, or phenylketonuria (PKU) after the birth of the baby. PKU is the inability to break down phenylalanine because of a missing enzyme, which results in the accumulation of this amino acid in the body and damage to nerve cells PKU can be treated with a special diet. Traits can be Autosomal or Sex-linked. Autosomal- Trait on the non-sex chromosome, will appear in both sexes equally Sex-Linked- Trait whose allele is located on the X chromosome. Mostly seen in Males, if it is recessive, and most are recessive. (If, recessive, must be on both X’s for a female to have it, but on the only X in a male to have it. Females that inherit the allele from one parent will be a “carrier”, so can pass the trait to offspring, but will not show that they have the trait.) Traits can be Dominant or Recessive: If the trait is autosomal dominant, every individual with the trait will have a parent with a trait. Recessive- An individual with the trait can have one, two or neither parent exhibit the trait. (Ex. Both parents are heterozygous or carriers) Heterozygous or Homozygous: Two people who are heterozygous carriers of a recessive allele will not show the trait but can produce children with the trait. Carriers—individuals who are heterozygous for an inherited disorder but do not show symptoms. Carriers can pass the allele to their offspring. Recessive traits – it takes two Many traits can be carried with no ill effects on the individual heterozygote, but individuals receiving two copies of the recessive allele are affected. If two heterozygotes cross, there is a 25% chance that any one offspring will have the recessive trait. Three human genetic disorders that result when an individual receives two copies of a recessive allele are: 1) Tay Sachs - which results in death before the age of five due to the inability to metabolize some lipids 2) Cystic fibrosis (cf) - which results in an excessive secretion of thick mucus that accumulates in the respiratory and digestive tracts; treatment is prolonging the life-span of these individuals 3) albinism - which is a complete absence of the pigment melanin; these people have very pale skin, white hair, and pink or blue eyes; vision impairment is common in people with albinism 17 Dominant traits – some alleles are more expressive than others Many traits are the result of the inheritance of a dominant trait, including freckles, farsightedness, broad lips, widows peak, and polydactyly - extra fingers and toes. If a dominant disorder is fatal, it will disappear from the population. The exception to this rule is fatal disorders that do not affect the individual until after they have had offspring. Huntington’s is a fatal genetic disorder that results in the deterioration of the nervous system, but symptoms are not developed until the individual is in their 40s to 50s (middle age). By that time they may have already passed the allele on to their children. Interpreting a Pedigree: Circle- Female Square- Male Shaded in Circle or Square-- Has trait/disorder Clear Circle or Square-- Does not show trait/disorder Carriers-- Sometimes designated Half shaded, Half Clear; or will be clear Horizontal Line between a Circle & Square indicates marriage Vertical Line extended from a parent line leads to the offspring When looking at a pedigree, you should be able to determine: # of generations, marriages, children, sex of individuals Birth order of children (1st born – last born, left to right) Phenotype of each person Sometimes, genotypes of each person for autosomal traits (if not, write a question mark for unknown allele ex. A? could be either AA or Aa for an autosomal trait); Sex linked genotypes are almost always able to be determined. Whether the trait is autosomal or sexlinked. Autosomal traits will typically be seen equally in males and females. Sex linked traits (on the X chromosome) will be seen more in males and the male will inherit it from the mother since he must get his Y chromosome from his Dad. Whether the trait is dominant or recessive. Dominant traits will be seen in each generation and one or both parents must show the trait if they have children who do. Recessive traits may or may not appear in each generation and one, both, or neither parent may show the trait if child(ren) do 18 Pedigree Practice Classwork Autosomal Pedigrees The pedigree shows the inheritance of attached earlobes. How many generations are shown? ______ How many married couples are shown? _____ Couple P1 had ___________ children and in what order? ______________________________ Is the trait for attached earlobes, versus free earlobes, dominant or recessive? ________________ How do you know? ______________________________________________________________ Fill in the genotypes on the pedigree. The pedigree shows the inheritance of tongue rolling. Is the trait dominant or recessive? ________________ Explain. ______________________________________________________________ ____________________________________________________________________ Fill in the genotypes on the pedigree. Sex-linked Pedigrees This pedigree shows the inheritance of colorblindness, a sex-linked trait. How many males have the disorder? ________ How many females? _________ In order to have a child with colorblindness does a parent have to be colorblind? ______ Is the trait dominant or recessive? ________________ Is the mother of the colorblind girl in the F3 generation colorblind, a carrier, or a person with normal color vision? ______________ Explain. ______________________________________________________________ Fill in the genotypes on the pedigree. 19 Name_______________________ Per____ (Homework due _____________) PEDIGREE WORKSHEET Autosomal Pedigree Remember, when a gene is autosomal, it can appear in BOTH sexes. This is an autosomal pedigree for dimples. P F1 F2 Is having dimples a dominant or recessive characteristic? ___________________________. Explain why. ____________________________________________________________. ______________________________________________________________________. How many generations are there? ___________. How many children does the P generation have? _________. What is the birth order of P’s children in the F1 Generation? ________________________________. How many men have dimples? ___________. How many females?_________. Critical Thinking: (Hint: Use a Punnett Square to help answer the following questions). In the P1 generation, is the mom heterozygous (Dd) or homozygous (DD/dd) for dimples? _________________________. Explain._______________________ _______________________________________________________________. In the P1 generation, is the dad heterozygous (Dd) or homozygous (DD/dd) for dimples? ________________________. Explain. ________________________ ______________________________________________________________. In the F2 generation where all the circles and squares are shaded in, is the dad heterozygous or homozygous for dimples?____________________________. Explain._______________________________________________________ ______________________________________________________________. What about the mother (heterozygous or homozygous)?__________________ Explain________________________________________________________ 20 Sex-linked Pedigree Remember, in sex-linked pedigrees, for a female to express the sex-linked condition she must carry the recessive allele on BOTH X’s which means she inherited the condition from both her father AND her mother. This is a sex-linked pedigree for colorblindness. With a pencil show which individuals are carriers of colorblindness by shading in the circle/box half way. (Hint: Use Punnett Squares to help you if needed). Label the generations P, F1, F2 Is colorblindness a dominant or recessive condition?____________________. Explain why.____________________________________________________ How many males are colorblind? __________ How many females?_________. Do you have to have a parent that is colorblind to be colorblind?___________. Is the mother of the colorblind female in the F2 generation colorblind, have normal vision, or is she a carrier?____________________________. Explain why_______________________________________________________ _________________________________________________________________ (Homework continued) 21 Name________________________________ Per____ Applied Genetics - © Prentice-Hall (Homework continued) A. Duchenne muscular dystrophy is a deadly disorder in which the muscles grow progressively weaker. The disease is caused by a recessive gene on the X chromosome. The pedigree chart below illustrates the inheritance of this gene. Use the chart to answer the questions that follow. HINT: Write the genotypes for each individual in the pedigree before you start answering the questions. Key: Normal female Normal male A C G Carrier female Female with disorder B D F E H Male with disorder I J K 1. Is Duchenne muscular dystrophy more likely to occur in males or in females? Explain your answer. _____________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 2. Individual H is a female with this disorder. Explain how she inherited the disease. _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 3. Individual K has this disorder, yet his father did not. Explain how this is genetically possible. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ______________________________________________________________________________________________________ 4. Individual G does not have the disease, yet his mother was a carrier and his father had the disease. Explain how this is possible. _______________________________________________________________________ ___________________________________________________________________________________________________ 5. Why is the genotype of the father unimportant when investigating sex-linked traits inherited by male offspring? ______________________________________________________ 22 (Homework continued) B. Huntington disease, a disease of the nervous system, is caused by an autosomal dominant gene. The pedigree chart below illustrates a family with individuals who have Huntington disease, the pedigree is incomplete, though, since all of the genotypes have not be filled in. Use the chart to answer the questions that follow. HINT: Write the genotypes for each individual in the pedigree before you start answering the questions. A B hh Hh C D E hh J F G H I hh K L Hh Hh M N O HH Key: H Female Male Huntington Disease h Normal Gene 6. What is the probable genotype of individual D? Explain your answer. _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 7. What are the probable genotypes of individuals H and I? Explain your answer. _______________________________________________________________________________________________________ _______________________________________________________________________________________________________ 8. What is the probability that N will not have Huntington disease? ________________ 9. Which individuals can be determined to have Huntington disease? ___________________________________ 10. Identify the individuals whose genotypes cannot be determined without more information. ______________________________________________________________________ 23