Question

The color of the eyes in plutonians is very important for their ability to properly see the objects in pluto. To determine the color of the eyes on early stages of development a test was developed using STRs.

There is an allele containing 10 repeats of 200nt and another one with 6 repeats. Plutonian with black eyes and 10/10 repeats had children with a female with orange eyes and 6/6 repeats. Their progeny was crossed with arecessive individual with 6/6 repeats. The progeny has 150 black 10/6; 120 orange 6/6; 17 black 6/6 and 13 orange 10/6. Is it possible to use these STRs as a test for eye color?

clear explanation please!

Answer 1

Short tandem repeats are inherited from each parent just like alleles are inherited.

Now, in present case, the gene of eye color has allele B for black and b for orange eye color

Parents: Black eyes with 10/10 repeats = BB 10/10, gametes = B 10

Orange eyes with 6/6 repeats = bb 6/6, gametes b 6

F1 generation : Black eyes 10/6 repeats = Bb 10/6

Gametes = B 10, B 6, b 10, b 6

Test cross of F1 (Bb 10/6) with recessive parent (bb 6/6)

Progeny of test cross

	B 10	B 6	b 10	b 6
b 6	Bb 10/6 black eyes	BB 6/6 black eyes	bb 10/6 orange eyes	bb 6/6 orange

Now, if the assortment of gene is independent to STR, the ratio should have been 1:1:1:1.

But in given ques, the ratio is 150:120:17:13 which is far different from expected ratio.

Also the parental types i.e.  black 10/6 and orange 6/6 are in higher ratio then recombinants which indicates that the STR is linked to eye color.

therefore, it is possible to use these STRs as a test for eye color.