Question

The wild-type color of horned beetles is black, although other colors are known. A black horned beetle from a pure-breeding strain is crossed to a pure-breeding green female beetle. All of their F1 progeny are black. These F1 are allowed to mate at random with one another, and 320 F2 beetles are produced. The F2 consists of 239 black, 61 brown, and 20 green. Use these data to explain the genetics of horned beetle color.
One hypothesis to explain the results is that:
A) two genes are involved with 12:3:1 epistasis, such that A_B_ and A_bb are black, aaB_ is brown, and aabb is green
B) two genes are involved with 12:3:1 epistasis, such that aabb and A_bb are black, aaB_ is brown, and A_B_ is green.
C) two genes are involved with 12:3:1 epistasis, such that A_B_ and A_bb are black, a_BB is brown, and AABB is green.
D) two genes are involved with 9:6:1 epistasis, such that A_B_ is black, A_bb and aaB_ are brown, and aabb is green.
E) two genes are involved with 9:4:3 epistasis, such that A_B_ is black, A_bb is brown, and aaB_ and aabb are green.

Answer 1

One hypothesis that explains the result is : A) Two genes are involved with  12:3:1  epistasis, such that A_B_ and A_bb are black, aaB_ is brown,and aabb is green.

Explanation:

• This is a case of Dominant Epistasis.
• When two genes are involved and presence of dominant allele of one gene masks the effect of either allele of the second gene then the epistasis is termed as dominant epistasis.
• In the given case black :brown: green ratio is approximately equal to  12:3:1.
• Here presence of a dominant A allele that is responsible for the black colour masks the effect of either allele of B. Therefore A_B_ and A_bb produces black beetles
• Again , absence of dominant A allows B to express itself and Brown beetles are produced thus aaB_ is brown.
• When both the genes are present as recessive alleles, neither brown nor black colour is expressed and the beetles are green.Thus, aabb are green.