Multiple Choice
An allele that exerts its effects whenever it is present is:
13. Mendelian Genetics
Genotype vs. Phenotype
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Color in squash is controlled by epistatic interactions in which color is recessive to no color. At the first locus, white squash (W) is dominant to colored squash (w). At the second locus, yellow (Y) is dominant to green (y). What is the phenotype of a squash with the genotype wwYy?
A
White
B
Green with yellow stripes
C
Green
D
White with yellow stripes
E
Yellow
Verified step by step guidance1
Understand that epistasis is a form of gene interaction where one gene masks or interferes with the expression of another. In this problem, the presence of a dominant allele at the first locus (W) results in a white squash, regardless of the alleles at the second locus.
Identify the genotype given: wwYy. Since the first locus is 'ww', the squash is not white because the dominant allele (W) is absent. This means the color can be expressed based on the second locus.
Examine the second locus: Y is dominant to y, so the presence of at least one Y allele (Yy) will result in a yellow squash.
Combine the information: Since the first locus allows color expression (ww), and the second locus has a dominant Y allele, the phenotype of the squash is yellow.
Conclude that the phenotype of a squash with the genotype wwYy is yellow, as the recessive 'w' allows color expression and the dominant 'Y' determines the yellow color.
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