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Q.
In genetics the term test cross means
Principles of Inheritance and Variation
Solution:
A test cross is a cross involving the mating of $F_1$
individual with the homozygous recessive parent. It is done
to find out homozygous and heterozygous individuals.
The off springs will be $100\%$ dominant if the individual was
homozygous dominant and the ratio will be $50\%$ dominant
and $50\%$ recessive in case of hybrid or heterozygous
individual. Here, $AaBb$, should be crossed with $aabb$. As
$aabb$ will produce only one type of gamete thus difference
in traits if observed in their progenies will be due to the
different gametes produced by hybrid dominant parent.
This will indicate the genotype of the dominant parent.