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Humanoids on the newly explored planet Brin (in a hypothetical galaxy in ~50 years from the present) have a gene structure similar to our own, but many very different plants and animals.
-One species of a small birdlike animal has an extremely variable tail length, an example of polygenic inheritance. Geneticists have come to realize that there are eight separate genes for tail length per haploid genome, with each gene having two alleles. One allele for each gene (a1, b1, and so on) increases the length by 1 cm, whereas the other allele (a2, b2, and so on) increases it by 0.5 cm. One bird was analyzed and found to have the following genotype: a1a1b2b2c1c2d1d2e2e2f1f2g1g1h1h2
What is the length of its tail?

Question

Quizplus · Accepted Answer

Each gene for tail length contributes either 1 cm or 0.5 cm to the total length. Therefore, the total contribution from the eight genes can be calculated as follows:

(a1a1): 1 cm
(b2b2): 1 cm
(c1c2): 1.5 cm (c1 contributes 1 cm, c2 contributes 0.5 cm)
(d1d2): 1.5 cm (same as c1c2)
(e2e2): 1 cm
(f1f2): 1.5 cm (same as c1c2)
(g1g1): 1 cm
(h1h2): 1.5 cm (same as c1c2)

Total contribution = 1 cm + 1 cm + 1.5 cm + 1.5 cm + 1 cm + 1.5 cm + 1 cm + 1.5 cm = 9 cm

Since the bird has two sets of each gene (as it is diploid), the total length of its tail would be 18 cm. However, the question asks for the length of one tail, not both. Therefore, the length of one tail would be half of 18 cm, which is 9 cm.

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