In fruit flies, the allele for red eyes, r, is dominant. which genotype represents a white-eyed male fruit fly?

The following choices are given;

A. XrXr. B. XrY. C. XRY D. XRXr

The answer is B. This is because the presence of the Y chromosome determines gender- which is male. In addition, it carries few genes than the X sex chromosome. Therefore, in this case, the X chromosome brings in the receive allele for eye color while the Y chromosome has no corresponding allele.

In most diploid organisms, they are two types of alleles for most genes which each on each set of chromosomes and at the same loci. In most cases, one allele is dominant over the other meaning that its presence masks the effect of the recessive allele.  In the absence of the dominant allele, the recessive allele is expressed . Usually, the recessive gene is disadvantageous to the individual.  

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