You perform a cross between two true-breeding strains of zucchini. One has green

Question

You perform a cross between two true-breeding strains of zucchini. One has green fruit and the other has yellow fruit. The F1 plants are all green, but when these are crossed, the F2 plants consist of 9 green : 7 yellow.

1. Suppose that the dominant alleles specify functional enzymes, and the recessive alleles are nonfunctional. Propose a biochemical pathway that could explain the gene interactions.

2. Is it possible to cross two different pure-breeding yellow zucchini strains and obtain all green progeny? What would be the genotypes of the parents and progeny?

3. Assuming that wild-type zucchini are green, how would you describe the phenomenon that occurred in the F1 of part (2)?

Explanation / Answer

1. If the ratio 9:7 is obtained then it means that the genes are in the same pathway. This may happen due to the absence of a regulatory protein that leads to low level of targeted gene transcription which is not sufficient to fulfil the cellular needs resulting in 9:7 ratio. Actually, regulatory gene binds to a regulatory site upstream of a target gene, facilitating the transcription of the gene.

This can also be interpreted as complementary gene interaction which means that the functions of both genes work together in the same biochemical pathway to produce a final product.

Green strain X Yellow strain - P GENERATION

GGYY X  ggyy

Gametes-GgYy

F1 generation- GgYy x GgYy

The F2 plants consist of 9 green and 7 yellow.

2.ggyy x ggyy- parent genotypes of yellow zucchini strains(pure breeding)

gametes - gy.gy

No it is not possible to cross two different pure-breeding yellow zucchini strains and obtain all green progeny. Progenies will have the same genotypes as parents i,e ggyy all yellow.

GY Gy gY gy GY GGYY GGyY GgYY GgYy Gy GGYy GGyy GgYy Ggyy gY GgYY GgYy ggYY ggYy gy GgYy Ggyy ggYy ggyy

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