In rainbow trout, body color is inherited in a Mendelian pattern, and blue body color is dominant to gray body color. A blue trout and a gray trout were crossed and produced 157 F1 offspring that were all blue. If two of these F1 offspring were then crossed and produced 200 offspring in the F2 generation, approximately how many F2 trout are homozygous dominant for this trait?A.0B.50C.100D.150
Question
In rainbow trout, body color is inherited in a Mendelian pattern, and blue body color is dominant to gray body color. A blue trout and a gray trout were crossed and produced 157 F1 offspring that were all blue. If two of these F1 offspring were then crossed and produced 200 offspring in the F2 generation, approximately how many F2 trout are homozygous dominant for this trait?A.0B.50C.100D.150
Solution
The original blue trout and gray trout that were crossed were likely BB (homozygous dominant for blue) and gg (homozygous recessive for gray) respectively. This is because all of their F1 offspring were blue, which indicates that the blue trait is dominant.
The F1 offspring would therefore all be Bg (heterozygous), having received one dominant blue allele from the blue parent and one recessive gray allele from the gray parent.
When two heterozygous (Bg) individuals are crossed, the expected phenotypic ratio is 3:1 (3 dominant to 1 recessive), and the expected genotypic ratio is 1:2:1 (1 homozygous dominant, 2 heterozygous, 1 homozygous recessive).
Therefore, out of 200 F2 offspring, approximately 1/4 (or 50) would be expected to be homozygous dominant (BB) for the trait. So, the answer is B. 50.
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