Which statement regarding genotype and phenotype is accurate?

Question

a. For autosomal recessive traits, the pheno-type is the same as the genotype.
b. The only trait in which phenotype always follows genotype is physiologic gender.
c. When a phenotype is fully penetrant, the trait is expressed in the heterozygous per-son.
d. Genotype changes as a person ages, whe-reas phenotype is not affected by the ag-ing process.

Answer 1

A
Genotype refers to the exact alleles of a single gene trait. Phenotype refers to the observable characteristics present when a gene is expressed. For recessive traits, because both alleles must be the same (homozygous) for the gene to be expressed, the phenotype and the genotype are the same. Dominant traits are expressed in the phenotype, even when the person's genotype is hete-rozygous for the alleles. Physiologic gender is not the only trait in which phenotype always fol-lows genotype, nor is a trait necessarily expressed in the heterozygous person because a pheno-type is fully penetrant. Also, both phenotype and genotype, as with other aspects of the genetic makeup of the individual, are affected by the aging process. The other statements are inaccurate descriptions of genotype and phenotype.