Question

Define and design a test-cross.​

Answer 1

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A test cross is performed to determine the genotype of a dominant parent if it is a heterozygous- or homozygous-dominant. For the purpose, a dominant parent is crossed with a homozygous recessive parent. A test cross between a heterozygous dominant (carrying one copy of dominant and recessive allele each) and recessive parent obtains dominant and recessive offspring in a 1:1 ratio while that between homozygous dominant and recessive parent gives all dominant progeny.

A cross between two pure breeding tall (TT) and dwarf (tt) varieties gives all tall F 1

progeny. To test genotype of F 1

progeny, it is crossed with pure breeding dwarf plant and obtains tall and dwarf progeny in a 1: 1 ratio suggesting the tested dominant variety is heterozygous.

Answer 2

Answer:

A cross between two pure breeding tall (TT) and dwarf (tt) varieties gives all tall F1 progeny. To test genotype of F1 progeny, it is crossed with pure breeding dwarf plant and obtains tall and dwarf progeny in a 1: 1 ratio suggesting the tested dominant variety is heterozygous.

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