Download Incomplete Dominance – 1 gene of a gene pair is incompletely

Genetics Problems
AP Biology
1. Incomplete Dominance – 1 gene of a gene pair is incompletely dominant over another.
In the heterozygous condition, a blending effect is observed.
Example: pink carnations
RR – Red
Rr – pink
rr – white
Make the following carnation crosses. Give genotypic and phenotypic ratios.
1. Red x pink
2. Pink x pink
3. Pink x white
2. In some plants, a true-breeding, red-flowered strain gives all pink flowers when
crossed with a white-flowered strain: RR (red) x (white)  Rr (pink). If flower position
(axial or terminal) is inherited as it is in peas, what will be the ratios of genotypes and
phenotypes of the F1 generation resulting from the following cross: axial-red (truebreeding) x terminal white? What will be the ratios in the F2 generation?
3. In once experiment, Mendel crossed a pea plant that bred true for green pods with one
that bred true for yellow pods. All the F1 plants had green pods. Which form of the trait
(green or yellow pods) is recessive? Explain how you arrived at your conclusion.
4.Mendel crossed a true-breeding tall, purple-flowered pea plants with a true-breeding
dwarf, white-flowered plant. All F1 plants were tall and had purple flowers. If an F1
plant self-fertilizes, then what is the probability that a randomly selected F2 offspring will
be heterozygous for the genes specifying height and flower color?
5. Two pairs of genes affect comb type in chickens. When both genes are recessive, a
chicken has a single comb. A dominant allele of one gene, P, gives rise to a pea comb.
Yet a dominant allele of the other (R) gives rise to a rose comb. An epistatic interaction
occurs when a chicken has at least one of the both dominants, P_ R _, which gives rise to
a walnut comb. Predict the F1 rations resulting from a cross between two walnut-combed
chickens that are heterozygous for both genes (PpRr).
6. A single mutant allele gives rise to an abnormal form of hemoglobin (HbS instead of
HbA). Homozygotes (HbSHbS) develop sickle-cell anemia. But the heterozygotes
(HbAHbS) show few outward symptoms. Suppose a woman’s mother is homozygous for
the HbA allele and her father is homozygous for the HbS allele. She marries a male who
is heterozygous for the allele, and they plan to have children. For each of her
pregnancies, state the probability that this couple would have a child who is:
a. homozygous for the HbS allele
b. homozygous for the HbA allele
c. heterozygous HbAHbS
7.In corn plants, a dominant allele I inhibits kernel color, while the recessive allele I
permits color when homozygous. At a different locus, the dominant gene P causes purple
kernel color, while the homozygous recessive genotype pp causes red kernels. If plants
heterozygous at both loci are crossed, what will be the phenotypic ratio of the F1
generation.
8. Red–green color blindness is caused by a sex-linked recessive allele. A color-blind
man marries a woman with normal vision whose father was color-blind. What is the
probability that they will have a color-blind daughter? What is the probability that their
first son will be color-blind?
9. A wild-type fruit (heterozygous for gray body color and normal wings) is mated with a
black fly with vestigial wings. The offspring have the following phenotypic distribution:
wild type, 778; black-vestigial; 785; black-normal, 158; gray-vestigial, 162. What is the
recombination frequency between these genes for body color and wing type?
10. A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal
phenotype. She marries a man who is normal for the trait. What is the probability
that a daughter of this mating will be a hemophiliac? That a son will be a
hemophiliac? If the couple has four sons, what is the probability that all four will be
born with hemophilia?
11. In another cross, a wild-type fruit fly (heterozygous for gray body color and red eyes)
is mated with a black fruit fly with purple eyes. The offspring are as follows: wild
type, 721; black-purple, 751; gray purple, 49; black-red, 45. What is the
recombination frequency between these genes for body color and eye color? Using
information from problem 9, what fruit flies (genotype and phenotypes) would you
mate to determine the sequence of the body-color, wing-shape, and eye-color genes
on the chromosome?
12. From a cross of AABbCC with AaBbCc, what is the probability that the offspring
will display a genotype of AaBbCc?