Genetics Problem set 3:
Due week of September 26

from book:

• Chapter 4, (3-point crosses)
  4.10, 4.13, 4.14, 4.16, 4.21 (4.36 and 4.39 if you want a challenge!)

To hand in:

1. In maize, a recessive allele "c" at the "color" locus produces dark colored kernels, a recessive allele "w" at the "waxy" locus produces waxy endosperm, and a recessive allele "b" at the "bronze" locus produces bronze leaves. All are on chromosome 9.

   Two pure-breeding varieties of corn were crossed to make an F1 that was heterozygous for all three genes. The F1 was then testcrossed to a line that was homozygous recessive for all three genes.

   Here are the results:

   Phenotype	N	Gamete type (parental, single recomb., double recomb.)	Expected number, if genes are assorting independently
   Colored kernels, waxy endosperm, normal leaves	340
   Bronze leaves	356
   Colored kernels	130
   Waxy endosperm, bronze leaves	140
   Colored kernels, bronze leaves	18
   Waxy endosperm	12
   Colored kernels, waxy endosperm, bronze leaves	3
   normal	1

   
   
   1. Draw a map of this chromosome showing the correct gene order and the relative distances between the three genes.
   2. What is the level of interference in this cross ?
   3. Two pure lines were crossed to make the triple heterozygote parent. What were the genotypes and phenotypes of those pure lines?
   4. Diagram the meiosis (in the F1 parent) that produced plants with colored kernels, normal endosperm, and normal leaves (row 3), showing the chromosomes and alleles at telophase of meiosis II.

    

2. Three genes, A, B, and C are all on the same chromosome. A is 10 map units to the left of B and C is 20 map units to the right of B. A triple heterozygote (ABC/abc) is testcrossed to a triple recessive (abc/abc). What phenotypes do you expect and what will be the frequency of each?
   (oops- it is hard to give phenotypes since I didn't say what the genes do! You can just use A and a to describe the dominant and recessive phenotype at the A locus, etc).

    

3. Here are three simple pedigrees showing the genotypes of parents and offspring.
   1. Which pedigree(s) can be used for linkage analysis?
   2. Label the offspring as recombinant, parental, or unknown.
   3. Using the informative pedigree(s), calculate the combined LOD score for the hypothesis that the genes are 20 cM apart.

      1. AB/ab   x   ab/ab
                 |
         AB/ab  ab/ab   aB/ab
         
         

      2. ab/ab	x  Ab/aB   
                 |
         AB/ab  ab/ab  aB/ab  ab/aB  ab/Ab
         
         

      3. Ab/ab 	x  ab/ab
         	|
         Ab/ab ab/ab Ab/ab  ab/ab