Dominant & Recessive Phenotypes
Dominant & Recessive
A natural question that arises is how can we translate genotypes to phenotypes; given a specific genotype, what phenotype will be displayed? This question is simplified in the case of homozygotes because both alleles correspond to the same phenotype.
For example, let's say that the B allele encodes the brown eye phenotype and the b allele encodes the blue eye phenotype. Then, it follows that a BB homozygote will certainly have brown eyes and a bb homozygous individual will definitely have blue eyes. However, what happens in the case of a heterozygous Bb individual?
In the case of eye color, a heterozygous Bb individual will have brown eyes. This brown eye phenotype (and therefore the B allele) is said to be dominant, whereas the blue eye phenotype (and the b allele) is recessive. In fact, in genotype notation, uppercase letters denote dominant alleles whereas lowercase letters denote recessive alleles.
Let's talk earlobes...
Humans can have either attached or detached earlobes. This earlobe phenotype is determined by a genotype. Through many studies, it has been determined that attached earlobes is a dominant phenotype and detached earlobes is a recessive phenotype (actually, this story recently got more complicated - read more here!)