What is a recessive allele?

question 7 options:

an allele that is only expressed when there are four present

an allele that is only expressed when no dominant allele is present

an allele that is acquired after birth

an allele that can never be expressed

B/2. An allele that is only expressed when no dominant allele is present.

Explanation:

Alleles always come in pairs, and we represent them with letters. Uppercase letters represent dominant alleles, and recessive alleles are represent by lowercase letters.

A recessive trait can only appear when the pair of alleles contains 2 lowercase letters, otherwise, if there are 2 uppercase letters or 1 of each, a dominant trait will be seen.

So:

AA - a pair of 2 dominant alleles (here we get a dominant trait).

Aa - a pair of 1 dominant and 1 recessive allele (here we get a dominant trait)

aa - a pair of 2 recessive alleles (here we get a recessive trait).

→ As we can see, we only get a recessive trait when there is a pair of 2 recessive alleles, therefore no dominant alleles in the pair.

Hope it helped,

BiologiaMgaister