Genetics Terminology

Front

Gene

Back

A transferable unit of heredity information passed from parent to offspring as a specific DNA nucleotide sequence that codes for a protein (usually) when expressed.

Front

Allele

Back

Alternate versions of a gene (DNA sequence) that typically code for a protein.

Front

Genotype

Back

Represents the allele combination for any 1 gene in diploid organisms; represented by letters and expressed as homozygous dominant (ex: AA), homozygous recessive (ex: aa), and heterozygous dominant (ex: Aa).

Front

Phenotype

Back

Observable traits (physical or behavioral) or cellular characteristics of an organism that are the result of the expression of its genes.

Front

Dominant (complete dominance)

Back

These alleles exert their phenotypic effects if at least one copy is present in the genotype; symbolized with an upper case letter (ex: B_).

Front

Recessive

Back

These alleles exert their phenotypic effect only if present as two copies, otherwise their effect is masked; symbolized with lower case letters (ex: bb).

Front

Homozygous

Back

Both alleles for a particular gene are identical in the same diploid organism, either both are recessive or both are dominant (ex: BB or bb).

Front

Heterozygous

Back

Alleles for a particular gene are different (ex: Bb) in the same diploid organism.

Front

Incomplete dominance

Back

Dominant allele does not completely mask the recessive allele and an intermediate (blended) phenotype is produced in heterozygotes.

Front

Codominance

Back

Dominant allele does not completely mask the recessive allele and both are equally visible in the phenotype of the heterozygote.