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In mice, black fur (B) is dominant over white fur (b). 

 
A testcross was performed to determine the genotype of a black mouse. What is the genotype of the mouse that was test crossed with the unknown black mouse? 
 
I put Bb, wouldn't it be bb for the other mouse?

1 month ago

Answered By Ibrahim A

According to Mendelian Genetics, the unknown black mouse being tested could be BB or Bb genotype. In order to determine the genotype, it would be test crossed with a bb (white fur phenotype) genotype. If the results from this test cross were all black mice (Bb) then the unknown black mouse genotype would be BB. If the results of the test cross were a ratio of 1:1 black:white (Bb:bb) then the unknown black mouse genotype would be Bb.

        b     b

   B   Bb  Bb

   B   Bb  Bb

        b     b

   B   Bb  Bb

   b   bb  bb