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Blue-eyed mice interbreed and produce progeny with a 2:1 ratio of blue to non-blue. When blue is crossed with nonblue, a 1:1 ratio of the two classes is obtained. Non-blues interbreeed to produce all non-blue offspring. Explain these observations. Support your explanation with details about phenotypes and genotypes.

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Explanation:

The results are explained if the trait blue eyes is dominant (B) over non-blue (b) and the dominant allele B is lethal in homozygous individuals.

The possible genotypes and phenotypes are:

  • Homozygous dominant (BB): lethal
  • Heterozygous (Bb): blue eyes
  • Homozygous recessive (bb): non-blue eyes

When blue (Bb) is crossed with non-blue (bb) the resulting offspring is 1/2 blue (Bb) and 1/2 non-blue (bb).

When non-blues interbreed (bb X bb) all progeny is non-blue (bb).

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