Genetics Homework
Q1. Epistasis
In Labrador retrievers coat color is controlled by two loci each with two alleles: B,b and E,e. When pure breeding black labs with genotype BBEE are crossed with pure breeding yellow labs of genotype bbee the resulting F1 offspring all have black coat. When a test cross is done with the F1 using a double homozygous recessive individual the following phenotypic ratios are typically seen.
1 Black: 1 Chocolate: 2 Yellow
a. List the alleles, genotypes and phenotypes. Which gene is epistatic?
b. What phenotypic ratios would you then expect from a heterozygous cross (BbEe x BbEe)?
Q2. X linkage
a. Red/Green colorblindness is a sex-linked recessive trait. A son and father are colorblind. The mother has normal vision. Did the son inherit colorblindness from his father?
b. Hemophilia is an X-linked recessive disorder. A normal woman has a father afflicted with hemophilia. She and a normal man have four children. Of these children two are male and two are female. Draw a pedigree assuming ideal proportions in the progeny. Indicate genotypes.
Q3. The recombination frequency is given below for several gene pairs. Create a linkage map for these genes showing the map units between loci.
J, K = 12 % K, L = 6% J, M = 9% L, M= 15%
Q4. Dihybrid cross.
In corn, colored aleurone (corn seed) is due to the dominant allele R. When homozygous, the recessive allele, r, produces colorless aleurone. The plant (leaf) color is controlled by another gene with two alleles, Y and y. The dominant Y produces green plants and the recessive y produces yellow plants. A Dihybrid plant was generated by mating a purebred green plant containing colored aleurone with a yellow plant containing colorless aleurone. The Dihybrid plant was test-crossed by mating it with a double homozygous recessive. The following progeny were generated:
Green colored: 88
Yellow colored: 12
Green colorless: 8
Yellow colorless: 92
a. Use the Chi Square to test whether the plant color gene obeys Mendel's Law of Random Segregation.
b. Use the Chi Square to test whether the aleurone gene obeys Mendel's Law of Random Segregation.
c. Use the Chi Square to test whether the plant color gene and the aleurone color obey Mendel's Law of Independent Assortment.
Tables showing your reasoning must be present for full credit.