Question
Explain test cross with suitable example and state its ratios.
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Answer
- A test cross is used to find out the genotype of any plant with dominant expression when it is not known whether it is homozygous (pure) or heterozygous for that trait.
- For example, a pea plant having purple flowers (F1 hybrid with unknown genotype) is crossed with a pea plant with white flowers (recessive).
- If all flowers produced are purple, we can conclude that plant is pure or homozygous and if we get purple and white flowers in a 1:1 ratio, conclude that plant is heterozygous.
- Following is the graphical representation for test cross:
- Assume that purple flower is Homozygous dominant (PP).
All flowers are purple. Thus, the F1 hybrid is homozygous dominant (PP). - Assume that purple flower is Heterozygous dominant (Pp).
Half of the flowers are purple and half are white. Thus, the F1 hybrid is heterozygous dominant (Pp).
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