Download Polygenic Inheritance and Epistasis

Polygenic Inheritance and Epistasis
1. Ear length in corn is the result of polygenic inheritance. Ear length is determined by
two pairs of genes. When both genes are homozygous dominant then the ear of corn
is long and when they are both recessive then the corn is short. The presence of a
heterozygous gene results in plants that have corn of various intermediate lengths.
a) Draw a Punnett square to show the result of a cross between a long (AABB)
plant and a short plant (aabb). What is the phenotype ratio?
b) Determine the phenotype of the offspring resulting from a cross between a
homozygous tall parent and a heterozygous medium plant.
2. a) The height of a weed is the result of polygenic inheritance involving three genes,
each which contribute 5 cm to the plant. The base (lowest height) is 10 cm and the
tallest is 40cm. Two plants that are both AaBbCc are crossed. Use a Punnett
square to determine the phenotype ratio.
b) If the tallest plant is 40cm and has a genotype of AABBCC, and each gene
contributes 5cm to the plant, what would be the height of each of the following
plants: AABBcc? aabbcc? AaBbCc?
c) If a plant that has the genotype AABBcc is crossed with a plant with a genotype
of aaBBcc, draw a Punnett square to determine the phenotype of the offspring.
3. Mouse coat colour is an example of epistasis. The dominant allele for colour (B)
results in black hair while the recessive allele results (b) results in brown hair. Yet
coat colour is affected by another gene which controls the depositing of pigment in
the fur. A recessive allele (c) allows no pigment to be deposited at all, resulting in
white mice. What is the genotype for the F1 generation of white mouse crossed with
a mouse that is homozygous for black hair and heterozygous for the pigment
deposition gene?
4. Flower colour in the sweet pea plant is an example of epistasis. Two genes are
involved. Both genes are required for the expression of coloured flowers. A
recessive pair of alleles on either gene results in white flowers. If two plants that are
both heterozygous for both genes (CcPp) are crossed. Draw a Punnett square and
determine the genotype and phenotype ratios.
5. Kernel colour in wheat is determined by an enzyme. The enzyme uses a precursor
molecule and produces a product which gives colour to the plant. The production of
this enzyme is controlled by two genes, yet only one dominant allele on either of the
two genes is required to generate the product and give colour to the plant. If a
purebred coloured plant (AABB) is crossed with a white plant (aabb) what would
be the genotype and phenotype of the F1 generation?