Question

Looking for help with Questions 1 and 2

Problem Set 5. Linkage and Mapping 1. It is observed that two heterochromatic knobs on chromosome 6 of maize have a chiasma between them in 20% of the meiocytes studied. What is the genetic map distance between these knobs? 2. In Upland cotton, the laciniate leaf and brown lint loci are 34 map units apart. What percentage of the meiocytes is expected to have a chiasma involving the region of the bivalent between these loci? 3. A heterozygous tomato plant, Rr Wf wf, was testcrossed to a rr wfwf plant. (R= red fruit, r = yellow fruit; and Wf = yellow flowers, wf = white flowers) The following progeny resulted:

Answer 1

1. The answer is 20 cMs or 20 map units.

In gene mapping, the percentage of recombination indiates the distance between the genes. This distance is measured in centi morghans (in the honor of Scientist Morghan), it is abbrivated as cM or in mapunits.

2. The answer is 17%, one cross over results two recombinants.

The formula for calculation of gene distance = % of recombinants/Total number of progeny *100.
As the distance here is 34 map units, as one cross ovre results two recombinants, the answer here is 34/2 = 17.So, 17% of meiocytes is expected to have a chaisma involving the region of the bivalnet between these loci.