The man has red hair. His sister has brown hair. Both of their parents have brown hair. Brown hair is caused by the dominant allele, B. Red hair is caused by a recessive allele, b. Complete the genetic diagram below to show how the man’s parents were able to have some children with red hair and some with brown hair. – 7075

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1. Both parents are brown (phenotype).

   Their genotypes are Bb (one dominant brown allele, one recessive red allele).

   Gametes produced: B and b from each parent.
   Possible offspring genotypes:
   BB
   Bb (×2)
   bb
   Offspring phenotypes:
   BB and Bb = brown
   bb = red
   So, there’s a 3 brown : 1 red ratio in the offspring.

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