3You are studying two linked genes in lizards You have two f

3.You are studying two linked genes in lizards. You have two females and you know that both are the same genotype, heterozygous for both genes (A/a and B/b).You test-cross each female to a male that is fully homozygous recessive for both genes (a/a and b/b) and get the following progeny with the following phenotypes:

Female 1                              Female 2 AB – 37                                 AB – 5 ab – 33                  ab – 4 Ab – 4                     Ab – 35

                aB – 6                                   aB – 36

How can you explain the drastic difference between these two crosses?

6 )In a transformation experiment, DNA of a p⁺q⁺ strain was used to transform a recipient strain that is auxotrophic for these markers. The number of each class of transformants is shown below:

Class

Genotype

Number

1

p+q+

405

2

p+q–

300

3

p–q+

195

4

p–q-

680

What is the map distance between these two loci?

Solution

Answer:

3. Analyzing the data from either cross alone or combining the data from both crosses for linkage, we see that the A and B loci are linked at a distance of 12.5 cM (10/80, 10/80 or 20/160 recombinants).

Since the recombinant classes ( Ab and aB for female 1; AB and ab for female 2) are different, the two maternal parents must have had the alleles at each locus in opposite cis-trans configurations.

For example, female 1 carried her dominant alleles in the cis configurations, while female 2 carried hers in trans.