Genetics: Penetrance, Expressivity, Epigenetics, and Inheritance Patterns

Penetrance

Whether or not a genotype actually produces the expected phenotype. Trick: WHETHER it shows.

Expressivity

The degree or amount to which a phenotype is expressed. Trick: HOW MUCH it shows.

Epigenetics

Changes in gene expression without changing the DNA sequence itself. Trick: Gene ON/OFF.

Sex-influenced trait

A trait controlled by an autosomal gene whose expression differs between males and females. Trick: AUTOSOMAL, but sex influences expression.

Sex-linked trait

A trait controlled by a gene located on a sex chromosome (X or Y). Trick: LINKED = located ON a sex chromosome.

Cytoplasmic inheritance

Inheritance of genes located in the cytoplasm, such as mitochondrial genes. Trick: CYTO = cytoplasm.

Autosomal trait

A trait controlled by a gene located on an autosome, meaning a non-sex chromosome. Trick: AUTO = not X or Y.

X-linked dominant trait

A dominant trait caused by a gene on the X chromosome. An affected father passes the trait to all daughters but no sons. Trick: Dad gives X to daughters and Y to sons.

X-linked recessive trait

A recessive trait caused by a gene on the X chromosome. It is often more common in males because males have only one X chromosome. Trick: Boys only have ONE X, so there is no second X to mask the recessive allele.