Download Mendelian Genetics Problems

Human and Nonhuman Mendelian Genetics Problems
1. If a woman with blood type A, one of whose parents had blood type O,marries a man with blood type AB,
what will be the theoretical percentage of their children with blood type A?
2. You are a genetic expert and asked to testify in court concerning the parentage of a baby. The mother of the
baby is blood type B. The baby is blood type O. The mother states that Mr. X is the father, but his blood type
is A. Could Mr. X be the father of the baby? Justify your answer by diagramming the genotypes of the mother,
father, and baby.
3. When rabbits with splashed white fur are crossed with black furred rabbits, their offspring are all slate blue.
When the slate blue rabbits are crossed among themselves, they produce splashed white, blue, and black
offspring in the ratio of 1:2:1, respectively.
a) How are these fur traits inherited?
b) Indicate the genotypes of each phenotype using appropriate symbols. Be sure to indicate the meaning
of the symbols.
4. Diabetes has been found to be inherited (in many cases) through a recessive allele “d.” How can two
nondiabetic parents have a diabetic child? Write down the genotypes of all three persons.
5. If the dominant gene “S” is necessary for sight, and the dominant gene “B” results in blindness no matter
what other genes are present, what percentage of the offspring produced by the cross ssBb and Ssbb will be
blind? Genes for sight (alleles S, s) and genes for blindness (alleles B, b) are on different chromosomes.
6. In the cross AaBbCC x AaBbCc
a) What fraction of the offspring would be expected to show dominant A and C phenotypes and
recessive b phenotype?
b) What fraction of the offspring would be expected to show all recessive phenotypes?
7. Four types of combs observed in chickens (single, rose, pea, and walnut) are determined by two genes.
The genes are on different chromosome pairs and each gene has two alleles each (R, r, and P, p). Single comb
results when chickens are homozygous recessive for both genes. Rose comb results when at least one dominant
R allele is coupled with recessive p. Peas comb occurs when at least one dominant P allele is coupled with a
recessive r. Walnut comb occurs when at least one dominant allele of each gene is present.
a) What are all the possible genotypes for each of the phenotypes (single, rose, pea, and walnut)?
b) Draw two different Punnett Squares for the cross between a single comb individual and a pea comb
individual. Hint: the pea comb individual can be two different genotypes.
c) What are the ratios of the four phenotypes (single, rose, pea, and walnut) for each of the crosses in b)?
8. You and a geneticist are looking at a brown mother dingbat with a newly born baby dingbat that is gold.
You wonder if the baby is male or female and the geneticist says it is obvious from the color what sex the baby
is. She explains that in dingbats genotype BB is brown and bb is gold; however, Bb is brown in males and gold
in females.
a) What is the genotype of the mother dingbat?
b) What is the sex of the baby dingbat?
c) What are the possible genotypes of the father dingbat?
9. When red-flowered snapdragons (R1R1) are crossed with white-flowered snapdragons (R2R2) all of the
offspring are pink.
a) Diagram the Punnett Square for a cross between two pink (R1R2) snapdragons.
b) What are the phenotypic ratios that are produced (Red:Pink:White)?
c) What is the name for this phenomenon?
10. Sam and Arlene both have a widow’s peak (that point that your hairline makes on your forehead). The
presence of a widow’s peak is heritable and dominant over a straight hairline. Sam and Arlene have a child,
Sarah, who does not have a widow’s peak.
a) What are the genotypes of Sam and Arlene with regard to the widow’s peak?
b) Diagram the Punnett Square (for widow’s peak) for the production of Sam and Arlene’s children.
c) Arlene is pregnant with another child. What is the probability that the new baby will have a widow’s
peak?
11. Sam and Arlene also have free earlobes which is also dominant to attached earlobes. Sarah has attached
earlobes.
a) What are the genotypes of Sam and Arlene with regard to earlobes?
b) What is the probability that the new baby will have free earlobes and a straight hairline? Hint:
Assume tht genetic control of earlobes and the widow’s peak are on different chromosomes.
12. A sex-inked recessive gene “r” produces red-green color blindness in humans. A normal woman whose
father was color-blind marries a color-blind man.
a) What genotypes are possible for the mother of the color-blind man?
b) Of all the girls produced by these parents, what percentage is expected to be color-blind?
c) What proportion of all the children is expected to be normal?
13. In cats the production of tortoiseshell coats is sex-linked. If a yellow male (Xb Y- ) mates with a black
female (XB XB ) the offspring are tortoiseshell females and black males.
a) Draw the Punnett Square for this cross.
b) Draw the Punnett Square for the cross between a yellow male and a tortoiseshell female. What
phenotypes, genotypes and ratios of the phenotypes are produced?
c) Would you expect to find many tortoiseshell male cats?
14. In Humans, a man (XY) with hairy ears will always have sons with hairy ears but never have daughters with
hairy ears. In fact, females (XX) very rarely have hairy ears. What does this say about the genetic system of
hairy ears in humans?