Question

a researcher used polymerase chain reaction (pcr) to test four individual diploid nematodes for the presence of a mutation in gene y. the researcher designed the reaction so that the dna fragments amplified from wild type and mutant alleles are 350 and 250 base pairs long, respectively. to identify the genotypes of the individual nematodes, the researcher visualized each pcr result by gel electrophoresis (figure 1). figure 1. gel electrophoresis of gene y pcrs in nematodes. the first four lanes contain the pcr product from individual nematodes a - d. lane 5 contains a dna ladder for size comparison. the size of each band in the ladder is labeled (bp = base pairs). which of the following claims is best supported by the data shown above? choose 1 answer: a nematode a is homozygous for the mutant allele. b nematode b is homozygous for the wild type allele. c nematode c is heterozygous for the mutant allele. d nematode d is heterozygous for the mutant allele.

Explanation:

1. Analyze the DNA fragment sizes: Wild - type allele gives a 350 - bp fragment, and mutant allele gives a 250 - bp fragment.
2. For Nematode A: The band is around 350 bp (matches wild - type size), so it should be homozygous wild - type, not mutant. So option A is wrong.
3. For Nematode B: The band is around 250 bp (matches mutant size), so it should be homozygous mutant, not wild - type. So option B is wrong.
4. For Nematode C: There are two bands, one around 350 bp (wild - type) and one around 250 bp (mutant). This indicates it has both alleles, so it is heterozygous for the mutant allele.
5. For Nematode D: The band is around 250 bp (mutant size), so it is homozygous mutant, not heterozygous.

Answer:

C. Nematode C is heterozygous for the mutant allele.