Mendelian Genetics

AP Biology· difficulty 2/5

A dihybrid cross between two RrYy plants. R (round) is dominant to r (wrinkled), and Y (yellow) is dominant to y (green).

RYRyrYry RYRyrYry RRYYRRYyRrYYRrYy RRYyRRyyRrYyRryy RrYYRrYyrrYYrrYy RrYyRryyrrYyrryy

What phenotypic ratio is expected among the offspring?

  • A

    9 round-yellow : 3 round-green : 3 wrinkled-yellow : 1 wrinkled-green

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  • B

    1:1:1:1

  • C

    9 wrinkled-green : 3 round-green : 3 wrinkled-yellow : 1 round-yellow

  • D

    3:1 round-to-wrinkled only

Explanation

The classic 9:3:3:1 ratio results from independent assortment of two heterozygous gene loci.

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