In cucumbers, heart-shaped leaves (h) are recessive to normal leaves (H) and having numerous fruit spines (ns) is recessive to having few fruit spines (Ns). The genes for leaf shape and for number of spines are located on the same chromosome; findings from mapping experiments indicate that they are 32.6 m. u. apart. A cucumber plant having heart-shaped leaves and numerous spines is crossed with a plant that is homozygous for normal leaves and few spines. The F1 are crossed with plants that have heart-shaped leaves and numerous spines. What percentage of the progeny would be expected to have normal leaves and numerous spines (H, ns)? Ignore the mapping function.

33.7%.

Explanation:

Given that:

Heart-shaped leaves (h)

Normal leaves (H)

Numerous fruit spines (ns)

Few fruit spines (Ns)

We are also told that: The genes for leaf shape and for number of spines are located on the same chromosome and are 32.6 m.u. apart.

A cucumber having Heart-shaped leaves and numerous spines is crossed with a plant that is homozygous for normal leaves and few spines.

Parent 1 (heart-shaped leaves and numerous spines)= hh nsns

Parent 2 (homozygous for normal leaves and few spines)= HH NsNs

Since the genes are located 32.6 m.u apart

Then, the recombinants should be 32.6% and each recombinant phenotype will be of 16.3%.

The non recombinants will be 67.4% and each non recombinant phenotype will be of 33.7%.

F1 progeny result will yield:

Recombinants:

Heart shaped leaves and few spines (h Ns)=16.3%

Normal leaves and numerous spines (H ns)=16.3%

Non-recombinants:

Heart shaped leaves and numerous spines (h ns)=33.7%.

Normal leaves and few spines (H Ns)=33.7%.

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