Download Genetic Problem Set

Genetic Problem Set
Follow all directions carefully. Be complete in your answers!
Example:
In pea plants, tall plants (T) are dominant to dwarf plants (t). In a genetic cross of two plants that are
heterozygous for the height (Tt), what would be the genotypic and phenotypic ratios of this cross?
Step 1:
Set up cross
Tt x Tt
Step 2:
Make Punnett Square
T
t
T
TT
t
Tt
Tt
tt
Step 3:
Write ratios:
Genotypes:
1 Homozygous dominant: 2 Heterozygous: 1 Homozygous recessive
Phenotypes:
3 tall: 1 dwarf
Monohybrid Crosses:
1. In pea plants, tall plants (T) are dominant to dwarf plants (t). In a genetic cross between an
individual that is homozygous dominant (TT) and an individual that is homozygous recessive (tt),
what would be the genotypic and phenotypic ratios of this cross?
2. In pea plants, yellow seeds (Y) are dominant to green seeds (y). In a genetic cross between an
individual that is heterozygous (Yy) and an individual that is homozygous recessive (yy), what
would be the genotypic and phenotypic ratios of this cross?
3. In pea plants, round seeds are dominant to wrinkled seeds. In a genetic cross between an
individual that is homozygous dominant and an individual that is heterozygous, what would be
the genotypic and phenotypic ratios of this cross?
4. In dogs, wire hair is dominant to smooth. In a cross of a homozygous wire-haired dog with a
smooth-haired dog, what would be the genotypic and phenotypic ratios of the F1 generation?
5. Woodrats are medium sized rodents with lots of interesting behaviors. You may know of them as
packrats. Let's assume that the trait of bringing home shiny objects is controlled by a single locus
gene and is dominant to the trait of carrying home only dull objects. Suppose two heterozygous
individuals are crossed. How many of each genotype would be expected if only 4 offspring were
produced?
6. In cattle, the hornless condition (H) is dominant and the horned condition (h) is recessive. A bull
without horns is crossed with a cow with horns. Of the four offspring, one (1) is horned and three
(3) are hornless. Determine the genotype of the bull and the cow.
7. In guinea pigs, curly hair (H) is dominant over straight hair (h). Give the phenotypic and
genotypic ratios of the F1 and F2 generations of a cross between a homozygous curly haired
guinea pig and a homozygous straight haired guinea pig.
Dihybrid Crosses:
8. In pea plants, purple flowers (P) are dominant over white flowers (p) and axial flower position
(A) is dominant over terminal flower position (a). If you cross two heterozygotes (AaPp) for both
traits, what would be the genotypic and phenotypic ratio of their offspring?
9. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are
controlled by single locus genes and are located on different chromosomes. Assume further that
normal coat color (N) is dominant to black (n) and brown eyes (B) are dominant to blue (b).
Suppose the alpha male and alpha female of a pack (these are the dominant individuals who do
most of the breeding) are black with blue eyes (alpha male) and normal colored with brown eyes
(alpha female), respectively. The female is heterozygous for both traits and the male is
homozygous for both traits. What would be the genotypic and phenotypic ratio of their offspring?
10. In humans, widow's peak (W) is dominant over a continuous hairline (w), and short fingers (F) are
dominant over long fingers (f). Two individuals with widow's peak and short fingers have a child
with continuous hairline and long fingers. Determine the genotype of the parents