Non-Mendelian Inheritance

Flashcards defining key vocabulary terms for Chapter 5: Non-Mendelian Inheritance, covering Maternal Effect, Epigenetic Inheritance, Genomic Imprinting, and Extranuclear Inheritance.

Maternal Effect

An inheritance pattern for certain nuclear genes in which the genotype of the female parent directly determines the phenotype of her offspring, regardless of the male parent's or offspring's own genotypes.

Limnaea peregra

A species of water snail studied by A. E. Boycott in which shell coiling orientation provided the first known example of a maternal effect gene.

Dextral Coiling

The right-handed body plan and shell orientation in $Limnaea\,peregra$, which is the dominant and more common phenotype produced when the maternal parent carries a dominant $D$ allele.

Sinistral Coiling

The left-handed body plan and shell orientation in $Limnaea\,peregra$, which occurs when the female parent is homozygous for the recessive $d$ allele.

Nurse Cells

Diploid maternal cells surrounding a maturing oocyte during oogenesis that transfer gene products (mRNA and proteins) into the egg.

Epigenetic Inheritance

An inheritance pattern in which a modification occurs to a nuclear gene or chromosome that alters gene expression in a cell-to-cell, reversible manner without changing the DNA sequence.

Dosage Compensation

A genetic mechanism that offsets or equalizes differences in the number of active sex chromosomes between males and females of a species.

Barr Body

A highly condensed, inactivated X chromosome found in the interphase nuclei of somatic cells in female mammals.

Lyon Hypothesis

The hypothesis proposed by Mary Lyon stating that dosage compensation in mammals occurs by the random inactivation of one X chromosome in female somatic cells early in embryonic development.

X-Chromosome Inactivation (XCI)

The epigenetic process in female mammals where one of the two X chromosomes becomes highly compacted and transcriptionally inactive in somatic cells.

Glucose-6-Phosphate Dehydrogenase (G-6-PD)

An X-linked enzyme involved in sugar metabolism used in $1963$ by Davidson, Nitowsky, and Childs to confirm the Lyon hypothesis at the cellular clone level.

X-Inactivation Center (Xic)

A short region on the mammalian X chromosome containing the $Xist$ gene that is required for X-chromosome counting and inactivation to occur.

Xist Gene

A gene located within the Xic that produces an RNA molecule which coats the target X chromosome and creates a nucleation site for inactivation.

Nucleation (X-Inactivation)

The initial phase of X-chromosome inactivation during embryonic development in which Xic regions are counted, one X remains active, and $Xist$ RNA binds to the targeted Xic.

Spreading (X-Inactivation)

The second phase of X-chromosome inactivation where condensation begins at the Xic and progresses toward both ends of the chromosome until it becomes a Barr body.

Maintenance (X-Inactivation)

The final stage of X-chromosome inactivation from embryonic development through adult life where the inactivated X chromosome is preserved as a Barr body during subsequent cell divisions.

Genomic Imprinting

An epigenetic phenomenon in which a DNA segment is marked during gametogenesis, resulting in monoallelic expression based on whether the gene was inherited maternally or paternally.

Monoallelic Expression

A expression pattern where offspring express only one of two inherited alleles (either paternal or maternal) while the other remains transcriptionally silent.

Igf2 Gene

A gene in mice encoding insulin-like growth factor 2 that undergoes paternal expression due to maternal imprinting, where the maternal allele is silenced.

Imprinting Control Region (ICR)

A DNA region located near an imprinted gene that is methylated during either oogenesis or spermatogenesis to regulate transcription factor binding and gene silencing.

Prader-Willi Syndrome (PWS)

A human genetic disorder characterized by reduced motor function, obesity, and small hands and feet, caused by inheriting a deletion on chromosome $15$ from the male parent.

Angelman Syndrome (AS)

A human genetic disorder characterized by hyperactivity, thinness, unusual seizures, and cognitive impairment, caused by inheriting a deletion on chromosome $15$ from the female parent.

Extranuclear Inheritance

The transmission of genetic traits controlled by DNA located outside the cell nucleus, specifically within mitochondria or chloroplasts (also known as cytoplasmic inheritance).

Nucleoid

A designated region within a mitochondrion or chloroplast that contains one or more copies of the circular double-stranded organellar chromosome.

Human Mitochondrial DNA (mtDNA)

A circular double-stranded genome of $17,000\,\text{bp}$ encoding ribosomal RNAs, transfer RNAs, and $13$ polypeptide subunits involved in oxidative phosphorylation.

Chloroplast DNA (cpDNA)

The circular double-stranded genome of chloroplasts, measuring $156,000\,\text{bp}$ in tobacco and carrying $110$ to $120$ genes for photosynthesis and translation.

Maternal Inheritance

A pattern of extranuclear inheritance where organellar genes are transmitted solely through the cytoplasm of the egg from the female parent.

Mirabilis jalapa

The four o'clock plant in which Carl Correns discovered maternal inheritance of green, white, or variegated leaf pigmentation.

Heteroplasmy

A cellular condition where a cell or individual contains a mixture of different organellar genomes, such as wild-type and mutant mitochondria or chloroplasts.

Three-Parent Baby Method

A reproductive technique combining nuclear DNA from both parents with healthy donor mitochondrial DNA into an egg to prevent passing on mitochondrial diseases.

Endosymbiosis Theory

The theory proposing that mitochondria and chloroplasts originated when primordial eukaryotic cells engulfed Gram-negative purple bacteria and cyanobacteria, respectively.