In order for a guinea pig to be hairless, it must have which alleles? A) Have no alleles B) Have two recessive alleles C) Have two dominant alleles D) Have one recessive and one dominant allele

What the question is really testing

This is a basic Mendelian genetics question about how dominant and recessive alleles affect what trait you can see (the phenotype).

When does a recessive trait appear?

A recessive trait appears only when an organism has two recessive alleles. If we let $H$ = hair (dominant) and $h$ = hairless (recessive), then:

• $HH$ = hair (dominant trait shows)
• $Hh$ = hair (dominant $H$ masks $h$)
• $hh$ = hairless (recessive trait shows)

Checking each answer choice

• A) Have no alleles: Not possible for a typical gene, you inherit alleles from parents.
• B) Have two recessive alleles: Correct, genotype must be $hh$.
• C) Have two dominant alleles: Would show the dominant trait (hair).
• D) Have one recessive and one dominant allele: Heterozygous $Hh$ would still have hair.

Quick takeaway

If the trait is recessive, you need a homozygous recessive genotype ($hh$) to express it.