Pedigree Analysis and Human Inheritance

This set covers essential vocabulary and concepts for pedigree analysis, including genetic terminology, standard pedigree symbols, and the characteristics of Mendelian and mitochondrial inheritance patterns.

Pedigree

A chart that shows the presence or absence of a trait within a family across generations.

Proband

The family member who initially comes to the attention of geneticists or clinicians, usually indicated on the pedigree by an arrow. It is called a propositus if male and a proposita if female.

Genotype

The genetic makeup of an organism, such as $TT$.

Phenotype

The physical, observable characteristics or traits of an organism, such as being tall or having freckles.

Dominant allele

An allele that is phenotypically expressed over another allele.

Recessive allele

An allele that is only expressed in the physical characteristics of an organism in the absence of a dominant allele.

Autosomal trait

A trait that is located on one of the $44$ autosomes, which are non-sex chromosomes.

Sex-linked trait

A trait that is located on one of the two sex chromosomes ($X$ or $Y$).

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

Having two different alleles for a particular gene.

Consanguineous mating

A mating or marriage between relatives, represented on a pedigree by a double horizontal line between the two individuals.

Monozygotic twins

Identical twins, depicted in pedigree charts by diagonal lines stemming from the same point with an additional horizontal line connecting the two symbols.

Dizygotic twins

Fraternal twins, depicted by diagonal lines stemming from the same birth point without a connecting horizontal line.

Vertical transmission

A pattern characteristic of autosomal dominant inheritance where the trait appears in every generation without skipping.

Incomplete penetrance

A situation where not everyone inheriting a mutant allele shows the phenotype, which can cause an autosomal dominant trait to appear to skip a generation.

Horizontal pattern

A pattern often seen in autosomal recessive pedigrees where the trait is not seen in parents or grandparents but appears among siblings.

SRY (sex-determining region of Y)

A gene found on the human $Y$ chromosome that encodes a protein that turns on other genes required for male development.

Hemizygous

The genetic condition of human males for X-linked genes, meaning they have only one copy of any X-linked gene and whatever allele they inherit determines their appearance.

Carrier

A woman who is heterozygous for a disease-causing X-linked recessive allele but usually does not display any symptoms herself.

Heteroplasmy

A unique aspect of mitochondrial genetics where a single cell or individual harbors both normal and mutant mitochondria, leading to variable expression of symptoms.