Suppose that there are three genes (called A, B, and C) that influence human ski
ID: 147729 • Letter: S
Question
Suppose that there are three genes (called A, B, and C) that influence human skin color. (In reality, there are many more genes that affect skin color!) For each of these three genes, a dominant allele (represented by a capital letter) increases the amount of pigment production by a fixed amount. All dominant alleles have an equal effect on the phenotype. Put these genotypes in order with respect to the phenotype they produce, from lightest skin color (least pigment) to darkest skin color (most pigment).
Explanation / Answer
A gene is represented by its two forms known as allele. They represent the dominant and the recessive version of the same gene. In the above example three genes (ABC) control one character that is skin color. When a trait/character is controlled by more than one gene then it is called as polygenic or multiple trait inheritance.
According to the above question capital letters A,B,C influence/control the dark pigmentation. And thew recessive allele of these three genes i.e. a,b,c will result in a lighter pigmentation as lower amount of pigment will be produces . During gamete formation alleles segregate to give rise to its different kinds. In this case eight different kinds of gametes will be produced that is as follows
Now the gametes come together in an offspring resulting in different types of skin color based on the number of dominant alleles in each genotype.
Gametes
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc
ABC
AABBCC
6
AABBCc
5
AABbCC
5
AABbCc
4
AaBBCC
5
AaBBCc
4
AaBbCC
4
AaBbCc
3
ABc
AABBCc
5
AABBcc
4
AABbCc
4
AABbcc
3
AaBBCc
4
AaBBcc
3
AaBbCc
3
AaBbcc
2
AbC
AABbCC
5
AABbCc
4
AAbbCC
4
AAbbCc
3
AaBbCC
4
AaBbCc
3
AabbCC
3
AabbCc
2
Abc
AABbCc
4
AABbcc
3
AAbbCc
3
AAbbcc
2
AaBbCc
3
AaBbcc
2
AabbCc
2
Aabbcc
1
aBC
AaBBCC
5
AaBBCc
4
AaBbCc
4
AaBbCc
3
aaBBCC
4
aaBBCc
3
aaBbCC
3
aaBbCc
2
aBc
AaBBCc
4
AaBBcc
3
AaBbCc
3
AaBbcc
2
aaBBCc
3
aaBBcc
2
aaBbCc
2
aaBbcc
1
abC
AaBbCC
4
AaBbCc
3
AabbCC
3
AabbCc
2
aaBbCC
3
aaBbCc
2
aabbCC
2
aabbCc
1
Abc
AaBbCc
3
AaBbcc
2
AabbCc
2
Aabbcc
1
aaBbCc
2
aaBbcc
1
aabbCc
1
aabbcc
0
Above is punnet square that is used to represent the genotype of the offspring. Below each genotype is a number representing the intensity of skin pigmentation with :
And rest are intermediates where skin color will be produced depending upon the number of dominant allele present.
Number
Genotype
0
aabbcc
1
Aabbcc, aaBbcc, aabbCc, aabbCc
2
AaBbcc, AabbCc, AAbbcc, AaBbcc, AabbCc, aaBbCc, aaBBcc, AaBbcc, AabbCc, aaBbCc, aabbCC, AaBbcc, AabbCc, aaBbCc,
3
AaBbCc,AABbcc,AaBBcc,AaBbCc,AAbbCc,AaBbCc,AabbCC,AABbcc,AAbbCc,AaBbCc,AaBbCc,aaBBCc,aaBbCC,AaBBcc,AaBbCc,aaBBCc,AaBbCc,AabbCC,aaBbCC,AaBbCc
4
AABbCc,AaBBCc,AaBbCC,AABBcc,AABbCc,AaBBCc,AABbCc,AAbbCC,AaBbCc,AABbCc,AaBBCc,AaBbCC,aaBBCC,AaBBCc,AaBbCC
5
AABBCc,AABbCC,AaBBCC,AABBCc,AABbCC,AaBBCC,
6
AABBCC
The table represents the total number of genotypes produced in the punnet square.
Gametes
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc
ABC
AABBCC
6
AABBCc
5
AABbCC
5
AABbCc
4
AaBBCC
5
AaBBCc
4
AaBbCC
4
AaBbCc
3
ABc
AABBCc
5
AABBcc
4
AABbCc
4
AABbcc
3
AaBBCc
4
AaBBcc
3
AaBbCc
3
AaBbcc
2
AbC
AABbCC
5
AABbCc
4
AAbbCC
4
AAbbCc
3
AaBbCC
4
AaBbCc
3
AabbCC
3
AabbCc
2
Abc
AABbCc
4
AABbcc
3
AAbbCc
3
AAbbcc
2
AaBbCc
3
AaBbcc
2
AabbCc
2
Aabbcc
1
aBC
AaBBCC
5
AaBBCc
4
AaBbCc
4
AaBbCc
3
aaBBCC
4
aaBBCc
3
aaBbCC
3
aaBbCc
2
aBc
AaBBCc
4
AaBBcc
3
AaBbCc
3
AaBbcc
2
aaBBCc
3
aaBBcc
2
aaBbCc
2
aaBbcc
1
abC
AaBbCC
4
AaBbCc
3
AabbCC
3
AabbCc
2
aaBbCC
3
aaBbCc
2
aabbCC
2
aabbCc
1
Abc
AaBbCc
3
AaBbcc
2
AabbCc
2
Aabbcc
1
aaBbCc
2
aaBbcc
1
aabbCc
1
aabbcc
0
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