In summer squashes (ie soft-squashes like zucchinis), fruitsmay be white, yellow

Question

In summer squashes (ie soft-squashes like zucchinis), fruitsmay be white, yellow or green. In 1 cross, a true-breedingyellow squash was crossed with a true breeding white squash. Al the F1s were white! When the F1 was crossed, the F2 resultswere: 12 white, 3 yellows and 1 green. a) How many genes are involved here? b) What are the genotypes of the parents, the F1and the F2? c) What type of allelic interaction is this? In summer squashes (ie soft-squashes like zucchinis), fruitsmay be white, yellow or green. In 1 cross, a true-breedingyellow squash was crossed with a true breeding white squash. Al the F1s were white! When the F1 was crossed, the F2 resultswere: 12 white, 3 yellows and 1 green. a) How many genes are involved here? b) What are the genotypes of the parents, the F1and the F2? c) What type of allelic interaction is this?

Explanation / Answer

Okay, there are two genes. We will use A and B. The genotype for atrue breeding white will be AABB. The true breeding yellow will beaabb. This was figured out using the given information. The firstcross gave all white F1's and the parents were truebreeding. That means the white phenotype is dominant. Since thereare three possible colors, this must involve two genes. Now createa punnett square, here is a great website for doing so:http://www.changbioscience.com/genetics/punnett.html When you cross the parents, AABB and aabb,the F1 offspring are all AaBb--white. Then cross twoAaBb's and you get the F2 generation: 1 AABB white, 2 AABb white, 1 AAbb white, 2 AaBB white, 4 AaBb white, 2 Aabb white, 1 aaBB yellow, 2 aaBb yellow, 1 aabb green Notice that as long as there is an A, the squash color is white.Two a's results in a yellow and all lowercase/recessive genesresults in a green. The interaction between these two genes iscalled epistasis, when one gene influences the expression ofanother gene.

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