Genotypes and phenotypes

Dominant allele

An allele represented by a capital letter that masks the expression of a recessive allele.

Recessive allele

An allele represented by a lowercase letter, expressed only when two copies are present.

Homozygous

Having two identical alleles for a specific gene inherited from both parents.

Heterozygous

Having two different alleles for the same gene.

Complete dominance

When a dominant allele is fully expressed and completely masks a recessive allele.

Carrier

A heterozygous individual who can pass on a recessive allele without displaying the trait.

Dominance vs. frequency

Dominant alleles are not necessarily more common in a population than recessive alleles.

Genotype

A set of letters representing an individual's allele combination for a trait.

Phenotype

An organism's observable characteristics influenced by its genotype and environment.

Environmental influence on phenotype

External factors like diet and exercise can alter observable traits alongside genes.

Codominance

When both alleles from a genotype are fully expressed in a heterozygote's phenotype.

Incomplete dominance

When neither allele is fully expressed, resulting in a blended phenotype in heterozygotes.

Sex-linked genes

Genes found on the sex chromosomes, primarily the X chromosome.

X-linked traits in males

Traits expressed fully in males because they possess only one X chromosome with no masking allele.

Transmission of X-linked traits

Affected males pass their abnormal X-linked gene to their daughters, but not to their sons.

Color blindness

A recessive X-linked trait that appears more frequently in males.