Question

In flower beetles, pygmy (py) is recessive to normal size (py+), and red color (r) is recessive to brown (r+). A beetle heterozygous for these characteristics was test-crossed to a beetle homozygous for pygmy and red. The following are progeny phenotypes from this testcross.

py+ r+ 178
py+ r 21
py r+ 19
py r 182
Total 400
What is the map distance between the py and r loci?
1) 0.10 cM
2) 10 cM
3) 90 cM
4) 40 cM
5) None of above

Answer 1

The map distance between the py and r loci in flower beetles is calculated based on the number of recombinant progeny, which is 40 (py+ r and py r+), divided by the total number of progeny, which is 400. The recombinant frequency is 10%, thus the map distance is 10 cM.

Step-by-step explanation:

To calculate the map distance between the py and r loci, we need to analyze the given progeny phenotypes from a testcross involving flower beetles. Recombinant progeny are those that have non-parental phenotype combinations, which in this case are py+ r and py r+. We count the number of recombinant progeny (21 + 19) and divide it by the total number of progeny (400), then multiply by 100 to get the percentage, which is also the map distance in centimorgans (cM).

Calculation:

• Recombinant progeny = 21 (py+ r) + 19 (py r+)
• Total progeny = 400
• Recombinant frequency = (40 / 400) * 100 = 10%
• Map distance = 10 cM

Therefore, the map distance between the py and r loci is 10 cM, indicating the frequency of recombination between these two genes in flower beetles.