Question

When considering a single character, the progeny of a test cross have a 1:1 ratio of dominant to recessive phenotypes.

1) the phenotype of the non-tester parent is

a) recessive

b) dominant

c) homozygous

d) heterozygous

e) not enough information to solve this problem

2) The genotype of the non-tester parent is

a) homozygous dominant

b) heterozygous

c) homozygous recessive

d) hemizygous

e) not enough information to solve this problem

Answer 1

Non tester parent refers to that parent whose genotype is not known. The genotype of non-tester parent is determined by doing test cross with a tester parent having homozygous recessive genotypic and recessive phenotypic condition for a particular character.

Since the result of our test cross is 1:1, so the non tester parent must have dominant phenotype and heterozygous genotype as in other condition we will not obtain 1:1 ratio in a test cross.

For example, Test cross 1: AA (non tester, homozygous dominant) X aa (tester) ----> Aa (all have dominant phenotype, so no 1:1 ratio).

Test cross 2: aa (non tester) X aa (non tester, homozygous recessive) ---> aa (all have recessive phenotype, so no 1:1 ratio).

Test cross 3: Aa (non tester, heterozygous) X aa (tester) ---> Aa & aa (half with dominant and half with recessive phenotype and genotype, so 1:1 ratio is obtained).

1. The correct option is Option b) Dominant

2. The correct option is Option b) Heterozygous