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Observe the four crosses given below : ...

Observe the four crosses given below :
(A.) `"TTrr"xx"ttRR"`
(B.) `"TrRr"xx"ttrr"`
(C.) `"TtRr"xx"TTrr"`
(D.) `"Ttrr"xx"ttRr"`
In which of the following crosses , 1: 1: 1: 1 ratio of progenies is obtained ?

A

A, C and D

B

A, B, C and D

C

B and D

D

A and B

Text Solution

AI Generated Solution

The correct Answer is:
To determine which of the given crosses results in a 1:1:1:1 ratio of progenies, we will analyze each cross step by step. ### Step 1: Analyze Cross A - "TTrr" x "ttRR" - **Parental Genotypes**: "TTrr" produces gametes: Tr and Tr (only one type). - "ttRR" produces gametes: tR and tR (only one type). - **Gametes**: Tr x tR - **Offspring Genotypes**: All offspring will be TtRr. - **Ratio**: Since all progeny are TtRr, the ratio is 100% TtRr, not 1:1:1:1. ### Step 2: Analyze Cross B - "TrRr" x "ttrr" - **Parental Genotypes**: "TrRr" produces gametes: TR, Tr, rR, rr (four types). - "ttrr" produces gametes: tr (only one type). - **Gametes**: TR, Tr, rR, rr x tr - **Offspring Genotypes**: Possible combinations are: - TR x tr = TtRr - Tr x tr = Ttrr - rR x tr = ttRr - rr x tr = ttrr - **Ratio**: The offspring will be TtRr, Ttrr, ttRr, and ttrr, resulting in a 1:1:1:1 ratio. ### Step 3: Analyze Cross C - "TtRr" x "TTrr" - **Parental Genotypes**: "TtRr" produces gametes: TR, Tr, tR, tr (four types). - "TTrr" produces gametes: Tr (only one type). - **Gametes**: TR, Tr, tR, tr x Tr - **Offspring Genotypes**: Possible combinations are: - TR x Tr = TTRr - Tr x Tr = TtRr - tR x Tr = TtRr - tr x Tr = TtRr - **Ratio**: The offspring will not produce a 1:1:1:1 ratio, as there are more TtRr than TTRr. ### Step 4: Analyze Cross D - "Ttrr" x "ttRr" - **Parental Genotypes**: "Ttrr" produces gametes: Tr, tr (two types). - "ttRr" produces gametes: tR, tr (two types). - **Gametes**: Tr, tr x tR, tr - **Offspring Genotypes**: Possible combinations are: - Tr x tR = TtRr - Tr x tr = Ttrr - tr x tR = ttRr - tr x tr = ttrr - **Ratio**: The offspring will be TtRr, Ttrr, ttRr, and ttrr, resulting in a 1:1:1:1 ratio. ### Conclusion The crosses that yield a 1:1:1:1 ratio of progenies are: - Cross B: "TrRr" x "ttrr" - Cross D: "Ttrr" x "ttRr" ### Final Answer The crosses that yield a 1:1:1:1 ratio of progenies are **B and D**.
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