Here's why:
* Testcross: A testcross involves crossing an individual with an unknown genotype (in this case, the heterozygote) with a homozygous recessive individual.
* Homozygous Recessive: The homozygous recessive individual will only produce one type of gamete (carrying the recessive allele).
* Heterozygote: The heterozygote will produce two types of gametes, one with the dominant allele and one with the recessive allele.
Example:
Let's say we have a heterozygous individual (Aa) and a homozygous recessive individual (aa).
* The heterozygote (Aa) will produce gametes: A and a
* The homozygous recessive (aa) will produce gametes: a and a
The possible offspring genotypes are:
* Aa (heterozygous)
* aa (homozygous recessive)
Since the dominant allele (A) masks the recessive allele (a) in heterozygotes, the phenotypic ratio will be 1:1:
* 1 dominant phenotype (Aa)
* 1 recessive phenotype (aa)
