Epigenetics and Non-Mendelian Inheritance Flashcards

Flashcards covering key concepts from lecture notes on X inactivation, genomic imprinting, sex chromosome abnormalities, and extranuclear inheritance.

Dosage compensation

A genetic mechanism in mammals that equalizes the expression of X-linked genes between males and females by turning off one X chromosome in female cells.

Genomic imprinting

An epigenetic process in which an allele is marked beyond the nucleotide sequence, causing expression to depend on whether it was inherited from the mother or the father.

Extranuclear inheritance

The transmission of genetic material found outside the nucleus, specifically within organelles like mitochondria or chloroplasts, typically following maternal lines.

Barr body

A condensed, inactivated X chromosome visible as a dark spot inside the interphase nucleus of female mammalian somatic cells.

Allozymes

Variant forms of an enzyme that differ in amino acid structure, shape, and charge, allowing them to migrate at different speeds (fast versus slow) on a gel.

G6PD

An enzyme involved in sugar metabolism used as an allozyme marker with fast and slow variants to prove random X-chromosome inactivation in tissue culture clones.

Lyon hypothesis

The principle stating that X-chromosome inactivation occurs randomly in early embryonic development and is permanently passed on to all descendant somatic cells.

Triple X syndrome

A sex chromosome variation in females ($\text{XXX}$) who possess two Barr bodies, are often fertile, and frequently present tall stature.

Turner syndrome

A chromosomal condition in females ($\text{XO}$) characterized by possessing only a single X chromosome and zero Barr bodies.

Klinefelter syndrome

A chromosomal condition in males ($\text{XXY}$) characterized by an extra X chromosome, the presence of one Barr body, male physiological development, and infertility.

Pseudoautosomal genes

Genes located on both the X and Y chromosomes that escape inactivation and are expressed from both sex chromosomes in a manner similar to autosomes.

Monoallelic expression

A phenomenon where only one copy of a gene (either maternal or paternal) is expressed in a cell while the other allele is epigenetically silenced.

IGF2

Insulin-like growth factor 2 gene, which served as a model system in mice to demonstrate genomic imprinting where only the paternal allele is expressed.

Imprint erasure

The phase during gametogenesis (spermatogenesis or oogenesis) where preexisting parental epigenetic marks are removed so new sex-specific imprints can be set.

DNA methylation

The addition of a methyl group ($\text{CH}_3$) to DNA bases, which compacts chromatin, prevents transcription machinery access, and silences gene expression.