Answer: A (AA x aa)
Explanation:
In option (A) both of the parent mussels are homozygotes, for alleles "a" and "A" respectively. Therefore, every single one (100%) of their offspring would be expected to be Aa heterozygotes. Combinations (B) and (D) yield a lower proportion of heterozygotes (50%), and combination (C) yields none at all. Punnett squares follow:
(A)
<u> | A A </u>
<u>a | aA aA </u>
<u>a | aA aA </u>
<u />
(B)
<u> | A a </u>
<u>A | AA Aa </u>
<u>a | aA aa </u>
<u />
(C)
<u> | A A </u>
<u>A | AA AA </u>
<u>A | AA AA </u>
<u />
(D)
<u> | A a </u>
<u>a | aA aa </u>
<u>a | aA aa </u>
<u />
Since the greenhouse effect causes the earth to be warmer than it would be without the atmosphere, the earth would be cooler and the temperature would be nearly 0 degrees fahrenheit instead of the average 59-60 degrees fahrenheit