Question

# In a typical Mendelian cross, which is a dihybrid cross, one parent is homozygous for both dominant traits and another parent is homozygous for both recessive traits. In the F2 generation, both parental combinations and recombinations appear. The phenotypic ratio of parental combinations to recombinations is

A
10:6
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B
12:4
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C
9:7
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D
15:1
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Solution

## The correct option is A 10:6 Gametes YR Yr yR yr YRYYRR YYRrYyRR YyRr YrYYRr YYrr YyRr Yyrr yRYyRR YyRr yyRR yyRr yrYyRr Yyrr yyRr yyrrIn a Mendelian cross which is dihybrid cross, the phenotypic ratio is 9:3:3:1. For example, if we cross between homozygous yellow and round (YYRR) and green and wrinkled (yyrr). Then the F1 generation will be heterozygote (YyRr) i.e all will be yellow and round. Now in the F1 generation four kinds of gametes are formed i.e YR,Yr, yR, ry which when selfed the result would be YYRR (round and yellow), YYRr (round and yellow) ,YyRR (round and yellow),YyRr (round and yellow) YYRr (round and yellow), YYrrYellow and wrinkled), YyRr(yellow and round),Yyrr (yellow and wrinkled)r, YyRR (yellow and round), YyRr (yellow and round), yyRR (green and round), yyRr (green and round), YyRr (yellow and round), Yyrr (yellow and wrinkled), yyRr(green and round), yyrr (green and wrinkled). The phenotypic ratio of parental recombinant would be 10:6. Thus, the correct answer is option A.

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