AN74.1-4 | Patterns of Inheritance — Glossary

One of two or more alternative forms of a gene at a particular locus on a chromosome

An inheritance pattern where a single copy of a mutant allele on an autosome is sufficient to produce the phenotype

An inheritance pattern requiring two copies of a mutant allele (homozygous state) on an autosome for phenotypic expression

An individual heterozygous for a recessive allele who does not express the disease phenotype but can transmit the allele to offspring

Mating between blood relatives, which increases the probability of offspring being homozygous for recessive alleles due to shared ancestry

The degree to which a penetrant genotype is phenotypically expressed, varying from mild to severe among affected individuals

The specific combination of alleles at a particular locus in an individual

Having only one copy of a gene, as in males for X-linked genes (single X chromosome)

The presence of a mixture of normal and mutant mitochondrial DNA within the same cell, leading to variable phenotypic expression

Having two different alleles at a particular locus, one on each homologous chromosome

Having two identical alleles at a particular locus, either both normal (homozygous wild-type) or both mutant (homozygous affected)

When not all individuals with a disease-causing genotype express the expected phenotype, expressed as a percentage less than 100%

The specific physical position of a gene on a chromosome

Inheritance pattern where both multiple genes (polygenic) and environmental factors contribute to the phenotype

A standardised diagrammatic representation of a family's genetic history across generations, using defined symbols for affected, unaffected, and carrier individuals

The proportion of individuals with a given genotype who actually manifest the expected phenotype

The observable physical or biochemical characteristics of an individual, resulting from the interaction of genotype and environment

The individual through whom a family with a genetic disorder is first brought to medical attention, indicated by an arrow in the pedigree

A model for multifactorial traits where disease manifests only when the combined genetic and environmental liability exceeds a critical threshold

An inheritance pattern where the mutant allele is on the X chromosome and produces disease in hemizygous males but not in heterozygous carrier females

Maternal inheritance pattern where all mitochondrial DNA is transmitted exclusively from the mother to all her children

The commonest form of short-limbed dwarfism, caused by a gain-of-function mutation in FGFR3 (autosomal dominant, 80% new mutations)

An autosomal recessive disorder caused by CFTR chloride channel mutations, characterised by thick secretions affecting lungs, pancreas, and sweat glands

The process of helping individuals and families understand and adapt to the medical, psychological, and familial implications of genetic contributions to disease

The probability that a genetic condition will occur again in a family, calculated based on the inheritance pattern and family history