Molecular Genetics Technology for Breeding Decisions in Equine Science

Gene

A stretch of DNA that helps determine a trait, often by coding for a protein.

Allele

Alternative versions of a gene that can exist at a specific locus.

Genotype

The allele combination an individual has (e.g., $AA$, $Aa$, or $aa$).

Phenotype

The observable outcome or expression of a trait.

Dominant allele

An allele that is expressed in the phenotype when at least one copy is present.

Recessive allele

An allele that is expressed only when two copies are present.

Mendel’s Law of Segregation

Allele pairs separate during gamete formation, so each gamete carries only one allele for each gene.

Mendel’s Law of Independent Assortment

Alleles of different genes assort independently into gametes.

Punnett square

A grid that combines possible gametes from each parent to predict offspring genotypes.

Monohybrid cross

A mating between two individuals who have different alleles for a single gene.

Genotype ratio

The ratio of different genotype combinations in the offspring.

Phenotype ratio

The ratio of observable traits in the offspring.

Test cross

Breeding an individual with a dominant phenotype to a known recessive genotype to determine the dominant genotype.

Transcription

The process of making an RNA copy of a gene from DNA.

Translation

The process of building a protein using the information in mRNA.

mRNA

Messenger RNA that carries genetic information from DNA to the ribosome for protein synthesis.

Codon

A sequence of three nucleotides in mRNA that specify an amino acid.

Artificial selection

Human-directed breeding to increase the frequency of desired traits.

Heritability

The proportion of phenotypic variation in a population that is attributable to genetic variation.

Inbreeding

Breeding between closely related individuals, which can increase the risk of harmful recessive alleles.

Genetic marker

A DNA sequence that is associated with a particular trait and can be used to guide breeding decisions.

Selection differential

The difference between the mean trait value of selected parents and the overall population.

Breeder’s equation

$R = h^2 S$; used to predict response to selection.

Linkage

The tendency of genes that are located close to each other on a chromosome to be inherited together.

Polygenic traits

Traits influenced by multiple genes, often exhibiting a range of phenotypes.

DNA replication

The process of making an identical copy of DNA before cell division.

Epistasis

The interaction between genes such that the presence of one gene affects the expression of another.