A test cross using an individual that is homozygous recessiv

A test cross using an individual that is homozygous recessive for three linked loci (r, s and w), is made with an individual that is heterozygous for all three loci (Rr, Ss and Ww). The following offspring are scored:

RSW (6)

            rSW (359)

            rsW (98)

            rsw (4)

            rSw(47)

            RsW (43)

            Rsw (351)

            RSw (92)

Based on these results, the order of the loci along the chromosome and the complement of alleles on the two homologous chromosomes in the heterozygous parent is: Order = SRW and heterozygous parent chromosomes are SrW + sRw

What is the cM distance between S/s and R/r?

A: 10 cM

B: 30 cM

C: 19 cM

D: 9 cM

E: 20 cM

Solution

The cM distance between S/s and R/r is E) 20cM

By Sorting according to reciprocal products and the final cM distance between S/s and R/r is 20cM