Question 7) Working Backwards Sometimes we only know about the offspring and we

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Question 7) Working Backwards Sometimes we only know about the offspring and we want to learn about the parents. If you have been paying attention, you should have started to notice a pattern. For example, when both parents are heterozygous the phenotypic ratio always comes out 3 to 1. If one parent is homozygous recessive and the other is heterozygous, the phenotypic ratio always comes out 1 to 1. Solve the next two problems In pea plants, yellow seeds (Y) are dominant and green seeds (v) are recessive. A pea plant with yellow seeds is crossed with a pea plant with green seeds. The resulting offspring have about equal numbers of yellow and green seeded plants. What are the genotypes of the parents? In another cross, a yellow seeded plant was crossed with another yellow seeded plant and it produced offspring of which about 25% were green seeded plants, what are the genotypes of both parents?

Explanation / Answer

Ans 1. Yellow seeds are dominant (Y) over green seeds(y)

When we crossed yellow seeds with green seeds, the resulting progeny have equal numbers of Yellow and green seeded plants, for this outcome one of the parent should be heterozygous.

P1 Yy X yy

Gametes Y, y X y, y

F1 Yy, Yy, yy, yy

Yellow seeded plants=1/2

Green seeded plants=1/2

So,the genotype of the parents are Yy and yy.

2. When we crossed the yellow seeded plant with another yellow seeded plant and the resulting progeny have 25% of green seeded plants, for this outcome both of the parents should be heterozygous to get the homozygous recessive phenotype.

P1 Yy X Yy

Gametes Y, y X Y, y

F1 YY, Yy, Yy, yy

Yellow seeded plants=3/4

Green seeded plants=1/4=25%

So,the genotype of both parents is Yy.

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