Mendelian and Non-Mendelian Inheritance Patterns

Flashcards covering Mendelian monogenic inheritance patterns, non-Mendelian traits, penetrance, expressivity, mosaicism, and key clinical example diseases.

Locus

The specific physical position or location of a gene on a chromosome.

Alleles

The different versions of a gene found at the same place (locus) on homologous chromosomes that code for the same character.

Homozygous

The genetic state of an individual who inherits two identical alleles for a specific gene.

Heterozygous

The genetic state of an individual who inherits two different alleles for a specific gene.

Autosomal Dominant Inheritance

A pattern of inheritance involving an abnormal dominant gene on an autosome, expressed when only one copy is present ($50\%$ child recurrence risk if one parent is heterozygous), affecting both genders equally in a vertical pattern.

Autosomal Recessive Inheritance

A pattern of inheritance requiring two mutated copies of a gene on an autosome pair ($25\%$ recurrence risk for carrier parents), typically presenting horizontally on a pedigree and often associated with consanguinity.

Recessive X-linked Inheritance

An inheritance pattern where the abnormal allele is located on the X chromosome, affecting males far more frequently than females ($1 \text{ in } 20$ males vs $1 \text{ in } 400$ females for color blindness).

Dominant X-linked Inheritance

An inheritance pattern caused by an abnormal dominant gene on the X chromosome, where females are affected more often than males, and an affected father passes the condition to all daughters but no sons.

Y-linked Inheritance

An inheritance pattern where the abnormal gene is located on the Y chromosome, affecting only males and passing directly from an affected father to all of his sons.

Mitochondrial Inheritance

A non-Mendelian pattern caused by mutations in mitochondrial DNA (a single loop of $16,569$ base pairs) transmitted exclusively maternally through the ovum.

Multifactorial Inheritance

A complex inheritance pattern resulting from a combination of multiple genetic factors and environmental causes, seen in conditions like ischemic heart disease and fractures.

Penetrance

An all-or-none phenomenon representing the proportion of individuals carrying a specific pathogenic variant who express detectable signs or symptoms of the condition.

Expressivity

The extent or degree to which a given genotype is expressed phenotypically among different individuals.

Phenotypic Expression

The observable physical or functional traits produced by an individual's genotype, which can show variable penetrance, variable expressivity, or both.

Mosaicism

The presence of two or more genetically distinct cell lines within a single individual, arising from a post-zygotic mutation during development.

Neurofibromatosis Type 1

An autosomal dominant genetic condition exemplifying variable expressivity, with manifestations ranging from café-au-lait patches to optic glioma and severe neurofibromas.

Auricular Hypertrichosis

A genetic condition characterized by excess hair growth on the ears that exhibits Y-linked inheritance.

Rett Syndrome

A genetic condition cited as following a dominant X-linked inheritance pattern.

Hemophilia

An X-linked recessive genetic bleeding disorder notably inherited through European royal lineages, such as that of Queen Victoria.