Solutions to Selected Homework Problems

# Genetics: A Conceptual Approach

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P Sam (white) X black F1 ½ white ; ½ black Interbred black X black F2 all black 3-17. Joe has a white cat named Sam. When Joe crosses Sam with a black cat, he obtains ½ white kittens and ½ black kittens. When the black kittens are interbred, all the kittens that they produce are black. On the basis of these results, would you conclude that white or black coat color in cats is a recessive trait? Explain your reasoning. 1:1 ratio in F1 indicates that one parent is heterozygous and the other parent is homozygous If black is recessive black = a; white = A If white is recessive black = A; white = a P white (Aa) X black (aa) F1 ½ white (Aa) ; ½ black (aa) Interbred black (aa) X black (aa) F2 all black (aa) CONSISTENT WITH RESULTS, SO BLACK IS RECESSIVE white (aa) X black (Aa) ½ white (aa) ; ½ black (Aa) black (Aa) X black (Aa) ¼ AA, ½ Aa, ¼ aa ¾ black ¼ white Not consistent with results Interbreeding of black cats only produced black kittens, so black kittens are homozygous

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Hairlessness ( h ) is recessive to hair ( H ) Is your dog with hair Hh or HH ? Determine using a test cross (cross your dog with unknown genotype to a homozygous recessive dog) H_ X hh TEST CROSS
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