In cucumbers, heart-shaped leaves (h) are recessive to normal leaves (H) and hav

Question

In cucumbers, heart-shaped leaves (h) are recessive to normal leaves (H) and having many spines (s)            is recessive to having few spines (S). The genes for leaf shape and number of spines are located on          the same chromosome; mapping experiments indicate they are 28 cMorgans apart.

     A cucumber plant with heart-shaped leaves and many spines is crossed with a plant that is true-breeding for normal leaves and few spines. The F1are crossed with plants that have heart-shaped leaves and many spines.

What phenotypes are expected in the progeny of this cross?

If you observe 100 progeny plants, how many of each phenotype would you expect?   

Please explain your answer.

Explanation / Answer

The recombinants should total 28%, so each recombinant phenotype will be 14% of the progeny. Since the F1 inherited a chromosome with heart-shaped leaves and many spines (hl ns) from one parent and a chromosome with normal leaves and few spines (Hl Ns) from the other parent, that are the non-recombinant phenotypes which together they total 72%, or 36% each. The 2 recombinant phenotypes are normal-shaped leaves with many spines (Hl ns) and heart-shaped leaves with few spines (hl Ns) .

       Heart-shaped, many spines             36%

       Normal-shaped, few spines             36%

       Heart-shaped, few spines               14%

       shaped-Normal, many spines 14%

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