Question

bio -> genetics **please explain answer

You use PCR analysis on DNA from a couple and their developing fetus to screen for a genetic defect. You find that both parents have one large and two small DNA bands, while the fetus has only the large DNA band. The most likely explanation for these results is:

Group of answer choices

All three are heterozygotes

Both parents are heterozygotes, the fetus is a homozygote

you cannot tell the allele combinations for the three individuals

The infant is a heterozygote and the parents are both homozygotes

Answer 1

The most likely explanation for this result is Both parent are heterozygous and the fetus is Homozygous ​​​​​​.

Both parents have two different allele for the genetic defect trait. One allele is the large DNA band. The other is cut into two small pieces by restriction enzyme and makes two different DNA bands.So they have one large and two small DNA bands. The fetus inherited same allele (belongs to large DNA band )from both parents, so he has only one large DNA band.