Question

Assume you are performing a cross between a plant that is heterozygous for the dominant traits red flowers and wrinkled seeds, with a plant that is homozygous for the recessive traits white flowers and smooth seeds. Assume the alleles are R for red flowers, r for white flowers, W for wrinkled seeds, and w for smooth seeds. The offspring of this cross show the following phenotypes:

43 red flowers and wrinkled seeds

7 red flowers and smooth seeds

9 white flowers and wrinkled seeds

41 white flowers and smooth seeds

What are the traits of the recombinant offspring in terms of flower color and seed shape? Explain how you know that these offspring are recombinant. What alleles would you expect to see in the individual chromosomes of each parent before and after crossing-over takes place? What is the recombination frequency? What is the distance between the genes in map units?

Answer 1

The traits of the recombinant offspring in terms of flower color and seed shape:

Red, smooth
White, wrinckled
These are recombinants because they are different with their parents. The genes are the same but they don't share the same alleles as parents.
The number of recombinants is always less than the number of parental types.

Genotype of parents: RrWw (red , wrinckled)
rrww (white , smooth)
after crossing over : Rrww
rrWw
(these two are the genotypes of recombinants)

recombination frequency = # recombinants / # total progeny
= 7+9 / 43+41+7+9 = 0.16
the genes are 16 m.u apart