Question

In a testcross, if all the offspring show the dominant phenotype, then the individual with the unknown genotype was (only pick one).

		heterozygous recessive.
		homozygous recessive.
		heterozygous.
		a clone of the other testcross individual.
		homozygous dominant.

Answer 1

Test crosses include the cross of a person who expresses a recessive form of the same trait. Analyzing the percentages of the dominant and recessive offspring determines whether the individual in question is heterozygous dominant or homozygous dominant. If all offspring from the test cross exhibit the dominant phenotype, the individual concerned is homozygous dominant and if half the offspring display dominant phenotypes and half exhibit recessive phenotypes, the individual is heterozygous dominant

In genetics, a test cross, first proposed by Gregor Mendel, which includes an individual's mating with a phenotypically recessive adult to assess the zygosity by comparing proportions of offspring phenotypes.

1- Heterozygous dominant

	T	t
t	Tt	tt
t	Tt	tt

In this case half of the offspring exhibit a recessive phenotype and half of them show the dominant phenotype, it indicates that both recessive and dominant alleles are transmitted to the offspring by the heterozygous parent. This will make the unknown parent a heterozygous dominant person dominant for that trait. There is a misprint in question it should be heterozygous dominant there is no such case like heterozygous recessive. So this option is incorrect.

2-Homozygous recessive

	t	t
t	tt	tt
t	tt	tt

In this case none of the offspring exhibit a dominant phenotype, it indicates that only recessive alleles transmitted to the offspring by the recessive parent. This will make the unknown parent a homozygous recessive for that trait. So this option is incorrect

3- Clone of other tests cross

In case of Clone of other test cross individual, it will give the same result as of homozygous recessive or heterozygous dominant and in that case, not all the offspring are dominant so this option is ruled out

4- Homozygous dominant

	T	T
t	Tt	Tt
t	Tt	Tt

In this case none of the offspring exhibit a recessive phenotype, it indicates that only dominant alleles transmitted to the offspring by the dominant parent. This will make the unknown parent a homozygous dominant for that trait. This is the correct answer to the question.