The round pea seed trait is dominant over the wrinkled pea seed trait. If the phenotype of a pea seed is wrinkled, which combination of genes must it have?

The wrinkled pea will have two recessive alleles on the locus.

Explanation:

Two forms of same gene are called alleles of that gene.

The allele that expresses itself under heterozygous condition is called the Dominant allele.

The recessive allele can express itself only if they are under homozygous combination i.e. both the alleles on homologous chromosome are recessive.

Here wrinkled pea is a recessive trait and if it is expressed in the phenotype then the genotype of the plant must be homozygous for the recessive allele.