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topix129 topix129
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11 years ago
black flies are dominant trait; white flies are a recessive trait. when a pure black fly is crossed to a white one, what fraction of the offspring is expected to be heterozygous? use the letter ''B''.
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wrote...
11 years ago
Pure black fly means the fly is homozygous dominant (BB) for the trait.

White flies have to be homozygous recessive (bb) because recessive traits are only expressed when they are homozygous.

So the cross of a pure black fly with a white fly is this: BB x bb

Use the Punnett Square method:
   B   B
b Bb  Bb
b Bb  Bb

As you can see, we have 4 Bb, which means 4/4 will be heterozygous for the trait!
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