3. Now let’s attach some meaning to genotypes. As you see from the previous problems, the genotype is an expression of the actual genetic makeup of the organism. The phenotype is the observable result of the genotype, i.e., what the organism looks like because of its genotype. Although phenotype is determined primarily by genotype, in many instances environmental factors can modify phenotype.
Human earlobes are either attached or free. This trait is determined by a single gene consisting of two alleles, F and f. An individual whose genotype is FF or Ff has free earlobes. This is the dominant condition. Note that the presence of one or two F alleles results in the dominant phenotype, free earlobes. The allele F is said to be dominant over its allelic partner, f. The recessive phenotype, attached earlobes, occurs only when the genotype is ff. In the case of complete dominance, the dominant allele completely masks the expression or effect of the recessive allele.
Suppose a man has the genotype FF. What is the genotype of his gamete (sperm) nuclei?