Which describes a trait from a recessive gene? a)it causes a mutation. b)it masks a dominant gene trait. c)it can appear if it is heterozygous. d)it usually appears only if it is homozygous.

It usually appears only if it is homozygous

Explanation:

According to Mendel's principles of inheritance, of which his law of dominance is one of them, an organism will receive two forms of gene for a particular trait called ALLELES from each parent.

Mendel discovered in his experiments that an allele is capable of masking the expression of another in a combined or heterozygous state. The allele that masks or is expressed is called DOMINANT allele while the allele that is masked is called RECESSIVE allele.

In a heterozygous state i.e. combined form of the different alleles, the dominant allele is phenotypically expressed over the recessive allele. Hence, the recessive phenotype or trait will only be expressed if the recessive allele are homozygous or same.