Complete question:
One gene has alleles A and a. Another has alleles B and b. Assume that you now study a third gene having alleles C and c. For each genotype, what type(s) of gametes will be produced
a. AABBCC
b. AaBBcc
c. AaBBCc
d. AaBbCc
Answer:
a. ABC
b. ABc, aBc
c. ABC, aBC, ABc, aBc
d. ABC, ABc, AbC, Abc, aBC, abC, aBc, abc
Explanation:
We have three genes that are not linked. Each gene can be in a dominant form or a recessive form. (A and a, B and b, C and c). Gametes are haploid sexual cells, n, meaning that they have half of the genetic material of a diploid cell. When two gametes get together, they form a diploid cell, the zygote.
As these genes are not linked, they segregate independently from each other. According to this, we can assume different allele combinations of these genes that form the gametes.
To know what kind of gametes might be formed from these genotypes, we just need to think about all the possible combinations according to the alleles of each gene. A gamete needs to have one allele of each gene.
An easy way to do so is to analyze genes separately and the possible combinations.
Genotype Possible alleles combination Gametes
a. AABBCC A----B----C ABC
In this genotype, there are only dominant alleles for each gene, so there is only one possible combination of alleles. A with B and C
b. AaBBcc A----B----c ABc
a----B-----c aBc
For this genotype, gene A has the dominant allele and the recessive one (A and a, respectively). Gene B has only dominant alleles (BB), and gene C only recessive alleles (cc). So we have two possible allele combinations: "A" with "B" and "c", and "a" with "B" and "c".
c. AaBBCc A----B-----C ABC
A----B-----c ABc
a-----B-----C aBC
a-----B-----c aBc
For this genotype, gene A has the dominant allele and the recessive one (A and a, respectively). Gene B has only dominant alleles (BB), and gene C has the dominant allele and the recessive one (C and c, respectively). So we have four possible allele combinations: "A" with "B" and "C", "A" with "B" and "c", "a" with "B" and "C", and "a" with "B" and "c".
d. AaBbCc A----B----C ABC
A----B-----c ABc
A-----b-----C AbC
A----b-----c Abc
a----B-----C aBC
a----B------c aBc
a-----b-----C aBC
a-----b-----c abc
This is a complete heterozygous genotype, which means that we have two options for each gene: the dominant allele and the recessive one. We have eight possible allele combinations.