Mendelian Genetics and Exceptions of Mendelian Inheritance
1. An organism with two copies of the same allele is.........................
2. An organism with two different alleles for a given locus is.........................
3. The allele for the black hair color (B) is dominant over the allele for the white hair color
(b) in guinea pigs. A test cross between a black female and a white male produced a litter
of six black guinea pigs. The genotype of the mother is..............................
4. When a pure strain of tall plants (T/T) with round peas (R/R) is crossed with short plants
(t/t) with wrinkled peas (r/r), how many different kinds of eggs can their offspring
produce?
5. How many different kinds of gametes can an organism of genotype A/a; B/B; C/c
produce?
6. When red-flowered snapdragons are crossed with white-flowered snapdragons, their
offspring have pink flowers. This type of inheritance is called...........
7. The genotypic expression seen in a person of blood group AB is called................
8. A child with blood-group genotype IA/IB is born with a woman with genotype IA/IB. The
father’s genotype can’t be .................
9. A trihyrid cross is made between two yeasts, both with genotypes A/a; B/b; C/c. What
proportion of the offspring will be of genotype a/a; b/b; c/c?
10. What is it that assorts independently, in keeping with the Law of Independent
Assortment?
11. In humans, two traits, widow’s peak and free-hanging earlobes, depend on separate
dominant genes on different chromosomes. A man with a widow’s peak and attached
earlobes (whose father has free-hanging earlobes) married a woman without a widow’s
peak but with free-hanging earlobes. Draw the pedigree of the family and show the
possible genotypes of each individual.
12. In Drosophilia, the mutation for ebony body color is recessive and autosomal (e) and
the white-eyed mutation is recessive and X-linked. Determine the phenotypes and
phenotypic ratios of the F1 and F2 generations for the following crosses:
a. white-eyed, ebony-bodied female X pure breeding wild-type male
b. reciprocal cross
13. In humans, red-green color blindness is inherited as an X-linked recessive trait. A
woman with normal vision, but whose father is color blind, marries a man who has normal
vision. Predict the genotypes and phenotypes of the woman, her husband and their male
and female offspring.
14. Tay-Sachs disease (TSD) is an autosomal recessive disorder that results in death by
the age of two. You are a genetic counselor and one day you interview a phenotypically
normal couple, where the male had a female first cousin (on his father’s side) who died
from TSD, and where the female had a maternal uncle with TSD. There are no other
known cases in either of the families and none of the matings are between related
individuals. Draw a pedigree of the families of this couple, showing the relevant
individuals.