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What is the pheno typic ratio of a dihybrid cross in F2 generation?
A cross made to study the inheritance of two characters or two pairs of contrasting forms or two pairs of different alleles is known as dihybrid cross.
Example:
Crossing of pure yellow, Round seeded plant with green, Wrinkled seeded pisum plants
Character -1 - seed colour Yellow --- green
Character - 2 - seed shape Round -----wrinkled
PHENOTYPIC HYPOTHESIS OF DIHYBRID CROSS

A. Crossing of ‘p’ generation:
Mendel crossed pure yellow, round seeded plant with pure green wrinkled seeded plant. He got all yellow,Round seeded plants in ‘F1’ generation. These are dihybrids.
The, ‘F1’ generation showed that yellow is dominant over green and round is dominant over wrinkled forms. This dominance was allready observed in monohybrid crosses.
B. Crossing of ‘F1’ individuals:
Mendel allowed ‘F1’ di hybrid yellow, round seeded plants for self pollination. He got different types of individuals in ‘F2’.They are,
1. Yellow, Round (Double dominant)
2. Yellow,Wrinkled (Recombinant-I)
3. Green, Round (Recombinant-Il)
4. Green, Wrinkled (Double recessive)
The above ‘4’ types of inidividuals are in the ratio of 9/1 6: 3/16: 3/16: 1/16 respectively.
‘F2’ ‘dihybrid ratio led mendel to propose the law of independent assortment.


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