8. You take a true-breeding tall vine, pear-shaped fruit tomato plant and cross

Question

8. You take a true-breeding tall vine, pear-shaped fruit tomato plant and cross it to a dwarf vine, spherical-shaped fruit tomato plant. The F1 are all tall fine, spherical fruit. You perform a testcross of the F1 to a dwarf vine, pear-shaped fruit plant. In the F2, you get the following progeny Tall, spherical 13 Dwarf, spherical 67 Tall, pear 73 Dwarf, pear 17 Are the genes linked? Explain. If so, what is the F1 heterozygote: coupling (cis) or repulsion (trans)? What is the map distance between the 2 genes?

Explanation / Answer

As the offspring is not in the 1:1:1:1 ratio which indicates that these two genes are linked.
As the genes are linked here, the high frequency categories are parents types and low frequency genotypes are recombinant types.

The F1 heterozgyote is in Trans configuration, so the parental categories are expressed with one dominant character only.

The Map distance = (No. of recombinants/ Total number of progey) *100
The Map distance = (13+17 / 13+67+73+17) * 100 = 17.64.

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