Genetics Problems Set 2

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Genetics Problems - Set 2

  1. In radishes the shape may be long, round or oval. Crosses between round and oval radishes gave 199 round and 203 oval offspring. Crosses between oval and oval radishes gave 121 long, 243 oval, and 119 round offspring. What type of inheritance pattern is this? Indicate the genotype of each phenotype.

  2. In humans, homozygotes have either straight or curly hair, and only heterozygotes can have wavy hair. From a mating between 2 wavy-haired individuals, what is the probability that 4 children in the family will have straight hair?

  3. When chickens with white feathers are crossed with black feathered birds their offspring are all grey. When grey individuals are crossed among themselves, they produce white, grey and black offspring. What type of inheritance pattern is this? Indicate the genotype of each phenotype.

  4. In Shorthorn cattle three coat colors occur: red, roan and white. Mating red with red or white with white produces only red or white offspring, respectively. Mating roan with roan results in red, roan and white calves in the proportion 1:2:1. What is the genotype of the roan animals? Mating a roan bull with only white cows results in 20 calves. Predict the most likely phenotypes and their proportion of these offspring. What type of inheritance is this?

  5. In a court case concerning a paternity dispute, each of two men claimed three children to be his own. The blood groups of the men, the children and their mother were as follows:





    On the basis of this evidence can the paternity of each of the three children be established? Give the genotype of the wife.









    first child




    second child




    third child




  6. In mice, the following are members of a multiple allele series: CA for yellow, CB for wild-type, CC for black. Individuals homozygous for the yellow allele die before birth. Alleles CA and CB are dominant to CC, and CA is dominant to CB. What phenotypic ratios would you expect from the following matings?

    1. CA CC x CA CC

    2. CA CC x CA CB

    3. CA CC x CB CC

  7. Tay-Sachs disease is a recessive phenotype (tt); it causes death by age 5. Achondroplastic dwarfism is caused by the heterozygous state (Aa) and the homozygous recessive genotype (aa) is lethal.

    1. Show the genotypes of the possible children resulting from a cross between parents who are heterozygous for both genes. Consider only live births as possible.

    2. In the previous cross, what fraction of the possible children will die before adulthood?

    3. What fraction of the possible children will be normal?

    4. What fraction of the possible children will have the normal phenotype with respect to the Tay-Sachs locus but will exhibit dwarfism?

    5. What fraction of the surviving children will not be carriers of either defective gene?

  8. Sickle cell anemia is a hereditary disease in humans. Severe anemia is found in the homozygous condition, aa, a milder form of anemia is found in heterozygotes, and normal individuals are homozygous for the dominant allele. In mating between two individuals suffering from mild anemia, 2/3 of the adult offspring also have mild anemia. What type of inheritance pattern is this? Explain these results. Provide the genotypes for all individuals described.

  9. Consider the following chicken genes. For the "creeper" gene, cc individuals are normal, heterozygotes have short legs (creepers), and the CC genotype is lethal, preventing chicks from hatching. For the feather color gene, B, the phenotype, black feathers is dominant to red feathers.

The Wager: A poultry breeder has two chickens: a black-feathered creeper cock (male) of genotype CcBb and a red-feathered creeper hen (female). A gambler bargains with the poultryman for the adult offspring produced from mating the two birds according to the following rules. The gambler will pay the poultryman $20 for each adult offspring with short legs and red feathers or normal legs and black feathers. However, the poultryman must pay the gambler $30 for each adult offspring with short legs and black feathers and $10 for each bird with normal legs and red feathers. Should the poultryman accept the wager? What potential margin of profit/loss does each person face? Show your work.

  1. In pigeons, checkered pattern is dominant to plain pattern, and red color is dominant to brown. An unknown pigeon, X bred with pigeon Y, (which is plain and brown) and produced checkered, red chicks. When pigeon X mated with pigeon Z (which is checkered and red) 2 plain brown chicks were produced. If pigeon X re-mates with pigeon Y, what is the probability that they will have a plain, brown offspring? Provide the genotypes of pigeons X, Y and Z.

  2. In guinea pigs, color pattern and ear shape are controlled by two X-linked pairs of alleles. Three varieties of color are possible: black, gray and white. The gray color occurs only in heterozygotes. Ear shape also has three possibilities: pointed, semi-pointed and round. The semi-pointed phenotype occurs only in heterozygotes. Two guinea pigs are mated and produce the following offspring: a white pointed male, gray round female, and a white semi-pointed female. What are the genotypes and phenotypes of the parents? What type of inheritance is involved?

  3. In Drosophila, white eyes is a sex-linked factor that is recessive to red eyes. Vestigial wings are recessive to normal wings, but these alleles are carried on autosomal chromosomes. Two flies when bred together produced 1600 offspring. Among the males, 300 were red, normal; 300 were white, normal; 100 were red, vestigial; and 100 were white, vestigial. Similar phenotypes were found among the female offspring. How many of these (the female) offspring would you expect to be white, vestigial? What are the genotypes of the parents?

  4. The black and yellow pigments in the coats of cats are determined by an X-linked pair of alleles. Males are either black (cb) or yellow (cy) Females are black, calico (with patches of black and patches of yellow), or yellow.

    1. A female has the following kittens in a litter: 2 calico females, 2 black females, 1 black male and 1 yellow male. What is the genotype of the parents?

    2. If a black female and a yellow male are crossed, what is the probability of getting a calico female?

  5. A child with blood type A, has a mother with blood type O. What blood types could the father have had?

  6. In humans, red-green color blindness is caused by a sex-linked recessive allele.

    1. If a normal man marries a normal woman whose father was color blind, what is the probability that they will have a color-blind son? List the genotypes of and phenotypes of all possible children.

    2. If a normal man mates with a color-blind woman, what is the chance that they will have a color blind son?

    3. If a normal man mates with a color-blind woman, what is the chance that they will have a color blind daughter?

  7. The allele for yellow body color in fruit flies is recessive and sex-linked. The dominant allele produced wild-type body color. What phenotypic ratios are expected from the following crosses?

    1. yellow male x yellow female, give F1 and F2

    2. wild-type male x yellow female; give F1 and F2

  8. A narrow, reduced eye called “bar” is controlled by a recessive, X-linked allele in fruit flies, while the normal, wild-type eye is produced by the dominant allele. A homozygous, normal female is crossed with a bar-eyed male

    1. determine the expected genotype and phenotype ratios in the F1 and F2.

    2. from this mating, what is the probability of producing a bar-eyed female in the F2?

    3. from this mating, what is the probability of producing a bar-eyed male in the F2?

  9. In humans, both color blindness and hemophilia are caused by recessive, sex-linked alleles. A color-blind boy whose clotting time is normal (without hemophilia) has a hemophilic brother with normal color vision. If the parents of the above children have another boy, what is the probability that he will be normal for both traits? Give the genotypes of all individuals.

  10. In humans, the allele for dark hair is dominant to the allele for red hair and the allele for right-handedness is dominant to the allele for left-handedness. A dark-haired, right-handed man mates with a red-haired, left-handed woman. Their first child has red hair and is left-handed.

    1. What are the genotypes of the parents?

    2. If the same couple have a second child, what is the probability that it will have dark hair and be right-handed?

  11. For each of the following pedigrees, determine the possible modes of inheritance.

(a) (b) (c) (d)

Practice Genetics Problems

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