Fruit flies homozygous for only the recessive allele, s^-, have bright red eyes.

Question

Fruit flies homozygous for only the recessive allele, s^-, have bright red eyes. Fruit flies homozygous for only the recessive allele, b^- have brownish-purple eyes. Fruit flies homozygous for both alleles (b^- and s^-) have white eyes. Fruit flies that simultaneously possess at least one wild type allele of both genes (s^+ _ and b^+_) have red or wildtype eyes. The b and s alleles arc independently assorting. Based on this information, determine whether the following statements are true or false. Please write the word true or the word false. Two genes control eye color in the fruit fly. A cross between fruit flies heterozygous for the alleles (b and s) you yield offspring with wildtype eyes in a proportion of 9/16. The initial precursor in a biochemical pathway that explains this data would be a red pigment. A test cross of a heterozygous fruit fly would yield 1/2 white eyed offspring.

Explanation / Answer

(a) TRUE

Reason -

Since control of eye color is encoded by a gene on the X-chromosome, females (XX) carry two copies and males (XY) only carry one. In females, the presence of a dominant red encoding allele (XW) will produce red eyes even if the individual in heterozygous for the white allele. Females can be

With only one copy of the X-chromosome, all males are hemizygous for this gene. They have only two options:

Hemizygous recessive - genotype: XwY; phenotype: white eyes.

(b) true

make a cross you will find the exact proportion of 9/16

(c) false

(d) true

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