Glossary – Monogenic (qualitative) inheritance

Use the alphabetical glossary below to remind yourself what the terms in the course mean.

Is there a term used in the course but missing here? Tell me in the comments box below and I'll add it.

Additive gene effect – each allele of a gene pair affects the individual’s appearance independently, neither masking nor attenuating the effect of the other. Also known as intermediate inheritance and codominance.

Allele – an alternative form of a gene; also called variant.

Autosomal – located elsewhere than on the sex chromosome.

Autosome – a chromosome other than a sex chromosome.

Breeding (selective breeding) – selection of the next generation of parent animals to change or maintain the characteristics of the animal population.

Causal gene/mutation – is sufficient to cause a change in the phenotype of an individual.

Chromosome – consists of a DNA strand.

Codominance – both alleles of a gene pair are expressed equally. Also called intermediate inheritance or additive gene effect.

Dominant – blocks the expression of a recessive allele.

Egg – female gamete, a reproductive cell.

Epistatic – a gene or genotype that masks the effect of a gene at another locus.

Epistasis – genes in different loci interact with each other.

Incomplete dominance – a dominant allele only partially masks the effect of the recessive allele.

Incomplete penetrance – a gene or genotype is expressed only in a proportion of individuals with the same genotype.

Gamete – reproductive cell; sperm or egg. An individual passes on its genes to its offspring through gametes.

Gene – a recipe for a protein.

Gene pair – a pair of alleles; one from the sire and another from the dam.

Genetic correlation – a measure of genetic association between traits. Genetic correlation is due to the same genes, or genes close to each other, influencing the two traits.

Genome – all the genetic material of an individual, all the DNA.

Genotype – an individual’s alleles in a particular gene or trait.

Heterozygous – a gene pair containing two different alleles of a gene.

Homozygous – a gene pair containing two identical alleles of a gene.

Hypostatic – a gene or genotype that is masked by the effect of a gene at another locus.

Lethal – an allele that leads to early (embryonic) death when homozygous.

Linkage – genes are so close together on the chromosome that they are usually inherited together.

Linkage disequilibrium – alleles in different loci occur together more or less often than you’d expect based on Mendel’s rules and statistics.

Locus – an address of the gene; the location of the gene on the chromosome.

Major gene – a gene that has a large effect but explains only part of the variation seen in a trait.

Mitochondria – an ‘energy plant’ of the cell, with its’ own DNA molecule.

Mitochondrial – located in mitochondria (mitochondria was discussed in the 2nd part of the course). Mitochondrial DNA is called mtDNA.

Modifier – a modifying gene with a small effect.

Mutation – a change in the DNA code; a genetic error.

Overdominance – the heterozygote trait is better than both the recessive and the dominant homozygote trait.

Penetrance – likelihood of an allele or genotype showing up in an individual’s phenotype.

Phenotype – appearance of an individual, a visible characteristic.

Pleiotropy – a gene controls more than one trait.

Polygenic trait – a trait that is controlled by more than one gene, usually dozens or even thousands.

Population – a group of animals (or people).

Recessive – appears only if an individual has received the same allele from both its’ sire and dam. Masked by a dominant allele.

Risk gene – predisposes to a certain genetic disorder.

Selective advantage – an individual has a trait or genotype that is favoured by natural selection or selective breeding. Selective advantage makes it more likely that an individual’s genes will thrive in a population.

Semilethal – an allele that, when homozygous, leads to early (embryonic) death in over 50 % but not 100 % of cases.

Sex-chromosomal – located on a sex chromosome.

Sex chromosome – X or Y chromosome.

Silencing – silencing of a chromosome or gene so that it cannot be read to form protein(s).

Sperm – male gamete, a reproductive cell.

X chromosome – female sex chromosome.

X-linked inheritance – a gene regulating a trait is located on the X chromosome.

Y chromosome – male sex chromosome.

Y-linked inheritance – a gene regulating a trait is located on the Y chromosome.

Zygote – a fertilised egg.

Is there a term used in the course but missing here? Tell me in the comments box below and I’ll add it.