The fur of a certain animal could be white or black. The expression of the genes
ID: 520091 • Letter: T
Question
The fur of a certain animal could be white or black. The expression of the genes for black pigmentation is under the control of two transcriptional activators whose genes are on two different chromosomes. A cross of two double heterozygotes is carried out.
Part A
If both transcriptional activators are required for black fur, what would be the ratio of black to white fur among the progeny?
Enter your answer as a reduced (!!!) ratio of black:white (in that order, just the numbers, no spaces). For example: 1:0, or 1:1, 2:1, 13:5, etc.
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Part B
If either transcriptional activators is enough for black fur, what would be the ratio of black to white fur among the progeny?
Enter your answer as a reduced (!!!) ratio of black:white (in that order, just the numbers, no spaces). For example: 1:0, or 1:1, 2:1, 13:5, etc.
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Explanation / Answer
Both genes are on different chromosomes. So, they segregate independently.
If we denote transcription factors as A and B, and show dominant alleles with upper case letters and recessive alleles with lower case letters, then double heterozygote genotype is AaBb.
If both transcription factors are required to have black fur, cross between double heterozygotes result in black and white furs in 9:7 ratio.
AB
Ab
aB
ab
AB
AABB
Black
AABb
Black
AaBB
Black
AaBb
Black
Ab
AABb
Black
Aabb
White
AaBb
Black
Aabb
White
aB
AaBB
Black
AaBb
Black
aaBB
White
aaBb
White
ab
AaBb
Black
Aabb
White
aaBb
White
aabb
White
If either of the transcription factors are enough to have black fur, cross between double heterozygotes result in black and white furs in 15:1 ratio.
AB
Ab
aB
ab
AB
AABB
Black
AABb
Black
AaBB
Black
AaBb
Black
Ab
AABB
Black
AABb
Black
AaBB
Black
AaBb
Black
aB
AaBB
Black
AABb
Black
AaBB
Black
AaBb
Black
ab
AaBb
Black
AABb
Black
AaBB
Black
aabb
White
AB
Ab
aB
ab
AB
AABB
Black
AABb
Black
AaBB
Black
AaBb
Black
Ab
AABb
Black
Aabb
White
AaBb
Black
Aabb
White
aB
AaBB
Black
AaBb
Black
aaBB
White
aaBb
White
ab
AaBb
Black
Aabb
White
aaBb
White
aabb
White
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