Question

For fruit flies, white bristles (sb+) are dominant to sepia bristles (sb), red eyes (be+) are dominant to brown eyes (be), and long bristles (s+) are dominant to short bristles (s). The parental genotypes for a series of crosses are wild-type males mated to homozygous recessive females. The F1 generation is heterozygous for all 3 traits regardless of sex. Several F1 generation testcrosses are performed and produces the following offspring:

sb be s212sb+ be+ s+198sb be+ s2sb+ be s+2sb be+ s+50sb+ be s53sb be s+41sb+ be+ s42Total600
What is the total map distance between these 3 genes to the nearest tenth (with one number after the decimal)? Units are cM or mu (i.e. if the answer is 11.4 centimorgans, report as 11.4 cM).

Answer 1

The total map distance between the three genes in fruit flies can be calculated based on the recombination frequencies. By determining the phenotypes of the parents and using the given offspring counts, we can calculate the recombination frequencies. The total map distance is the sum of these frequencies.

Step-by-step explanation:

The question is asking for the total map distance between three genes in fruit flies: white bristles (sb+) dominant to sepia bristles (sb), red eyes (be+) dominant to brown eyes (be), and long bristles (s+) dominant to short bristles (s) in the F1 generation. The parental genotypes for the crosses are wild-type males mated to homozygous recessive females, resulting in heterozygous F1 generation for all three traits. Testcrosses were performed and produced different offspring counts for each phenotype.

To calculate the map distance, we need to determine the order of the three genes and the recombination frequency between each adjacent pair of genes. The total map distance is the sum of the recombination frequencies between all three pairs of genes.

Based on the given offspring counts, we can determine the phenotypes of the parents and calculate the recombination frequencies. In this case, we can determine that the sb and be genes are located closer together than the be and s genes.

Using the formula:

Map distance = (Recombinant offspring / Total offspring) x 100%

We can calculate the map distances:

• sb-be = (53 + 41) / 600 x 100% = 16.33%
• be-s = (50 + 2) / 600 x 100% = 8.67%

The total map distance is the sum of these two distances:

Total map distance = 16.33% + 8.67% = 25%