Inbreeding

Inbreeding is reproduction between genetically related individuals. It increases the chance that offspring inherit identical copies of an allele from both parents.

Identity by descent: Alleles are identical by descent when they descend from the same allele in a shared ancestor. Inbreeding increases the chance that an offspring’s two allele copies are identical by descent.
Founder effect: A change in allele frequencies caused when a new population is established by a small number of individuals. Founder populations can have elevated relatedness and unusually frequent inherited disorders.
Selective breeding: The deliberate mating of organisms to increase the frequency of desired heritable traits. Breeders sometimes use inbreeding to fix traits, while managing associated fitness costs.
Outbreeding: Reproduction between individuals that are less closely related than the population average. It generally lowers offspring homozygosity relative to mating among close relatives.
Inbreeding coefficient: A probability measure that an individual’s two alleles at a locus are identical by descent. It quantifies the genetic consequence of an individual’s parents being related.
Genetic load: The reduction in population fitness caused by deleterious genetic variants. Inbreeding can expose recessive variants that contribute to genetic load.
Line breeding: A breeding strategy that maintains descent from a valued ancestor while limiting close-relative matings. It is a controlled form of inbreeding used to preserve particular lineages or traits.
Outbreeding depression: Reduced fitness in offspring from genetically or ecologically divergent populations. It shows that crossing distant lineages can carry costs unlike those of inbreeding.
Homozygosity: A genotype state in which both copies of a gene or genetic marker carry the same allele. Inbreeding raises homozygosity across the genome, including at harmful recessive variants.
Purging of deleterious alleles: The reduction of harmful recessive alleles when selection removes individuals in which those alleles are expressed. Inbreeding may enable purging, though its short-term fitness costs can be severe.

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