Transcript Set 4 - The Science Spot

T. Trimpe 2008 http://sciencespot.net/
In Dalmatians, the trait for black spots (B) is dominant over the
recessive trait for no spots. Use this information to answer
these questions.
(1) Two Dalmatians with black spots have puppies. One of the dogs is
homozygous for black spots, while the other is heterozygous. Out of a litter of
4 puppies, how many would you expect to have without spots? Create a
Punnett square to support your answer.
(2) Two Dalmatians had a large litter of 10 puppies. Seven of them have black
spots, while 3 do not. What would the genotypes of the two parents need to be
for this result? Create a Punnett square to support your answer.
(1) Two Dalmatians with black spots have puppies. One of the dogs is
homozygous for black spots, while the other is heterozygous. Out of a litter of
4 puppies, how many would you expect to have without spots? Create a
Punnett square to support your answer.
B
B
B BB BB
b
Bb Bb
None of them would be all white, since all
the offspring would have black spots.
(2) Two Dalmatians had a large litter of 10 puppies. Seven of them have black
spots, while 3 do not. What would the genotypes of the two parents need to be
for this result? Create a Punnett square to support your answer.
B
B
B
b
B
b
B BB BB
b
Bb
bb
B BB Bb
Bb Bb
b
Bb
bb
b
b
Bb
bb
The parents would have both have to be Bb or heterozygous for black spots
in order to have 7 out of 10 or about 75% of puppies with black spots.