Question
Long Answer Questions
What is dihybrid cross? Explain with suitable example and checker board method.
What is dihybrid cross? Explain with suitable example and checker board method.
✓
Answer
(1) A cross which involves two pairs of alleles is called a dihybrid cross. A phenotypic ratio of $9: 3: 3: 1$ obtained in the $F _2$ generation of a dihybrid cross is called a dihybrid ratio.
(2) Thus for example, when we cross a true breeding pea plant bearing round and yellow seeds with a true breeding pea plant bearing wrinkled and green seeds we get pea plants bearing round and yellow seeds in the $F_1$ generation.
(3) When $F_1$ plants are selfed, we get a ratio of $9: 3: 3: 1$ in the $F_2$ generation, where $9$ plants bear yellow round seeds, $3$ plants bear yellow wrinkled seeds, $3$ plants bear green round seeds and 1 plant bears green wrinkled seeds.
(4) Parents $\left(P_1\right)$ : $RRYY$ $\times$ $rryy$
Gametes of $P _1$ $RY$ and $ry$
$F _1$ generation: RrYy(Yellow round)
On selfing $F _1$ : $RrYy$ $\times \operatorname{Rr} Y y$
Gametes of $F_1$ : $RY, Ry, rY, ry$
$P_2$ generation:
Round Yellow : $9$ Round green : $3$ Wrinkled yellow : $3$ Wrinkled green : $1$
Phenotypic ratio : $9 : 3 : 3 : 1$
Genotypic ratio : $1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1$
(2) Thus for example, when we cross a true breeding pea plant bearing round and yellow seeds with a true breeding pea plant bearing wrinkled and green seeds we get pea plants bearing round and yellow seeds in the $F_1$ generation.
(3) When $F_1$ plants are selfed, we get a ratio of $9: 3: 3: 1$ in the $F_2$ generation, where $9$ plants bear yellow round seeds, $3$ plants bear yellow wrinkled seeds, $3$ plants bear green round seeds and 1 plant bears green wrinkled seeds.
(4) Parents $\left(P_1\right)$ : $RRYY$ $\times$ $rryy$
Gametes of $P _1$ $RY$ and $ry$
$F _1$ generation: RrYy(Yellow round)
On selfing $F _1$ : $RrYy$ $\times \operatorname{Rr} Y y$
Gametes of $F_1$ : $RY, Ry, rY, ry$
$P_2$ generation:
Round Yellow : $9$ Round green : $3$ Wrinkled yellow : $3$ Wrinkled green : $1$
Phenotypic ratio : $9 : 3 : 3 : 1$
Genotypic ratio : $1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1$
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