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Puzzling Adventures: Alien Genetics Problem #3 Solution




Cloe Liane Shasha

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Problem 3 Answer: The only genetically important sexes are S2, S3 and S4. A majority is sufficient to determine whether an individual will look as if it is a B or b.

To return to problems 1 and 2, we have BBb among all the first-generation children.

In the second generation, we will get 27 possible genetic combinations among the progeny:

BBB
BBB
BBb
BBB
BBB
BBb
BbB
BbB
Bbb

BBB
BBB
BBb
BBB
BBB
BBb
BbB
BbB
Bbb

bBB
bBB
bBb
bBB
bBB
bBb
bbB
bbB
bbb

Of these combinations, seven have the b phenotype. Thus the ratios are 20/27 (about 74%) with B phenotype and 7/27 (about 26%) with b phenotype. In the last experiments, the ratios of B and b are reversed.

The ones that have b phenotypes in the second generation could have the following makeup:

Bbb
Bbb
bBb
bBb
bbB
bbB
bbb

More than 15% of their children will be B (approximately 17.5% in fact, as you might calculate).

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