Genetics Lecture 13- Chromosome Variation (Structure and Number)

Vocabulary practice flashcards covering variations in chromosome structure (deletions, duplications, inversions, and translocations) and chromosome number (aneuploidy and polyploidy), based on Genetics 380 Lecture 13.

Euploid

An organism or cell whose chromosome complement consists of one or more complete sets of chromosomes.

Aneuploid

An organism or cell that varies from the normal condition by individual chromosomes rather than complete sets, possessing one or more incomplete sets.

Chromosomal Rearrangements

Mutations involving changes in the structure of chromosomes caused by one or more breaks in the DNA, cellular repair mistakes, or unequal genetic recombination.

Exonucleases

Enzymes that degrade and destroy nucleic acids at exposed, unstable free ends of broken DNA molecules.

Deletion

A chromosomal structural mutation characterized by the loss of a chromosomal segment following a break and subsequent enzymatic degradation.

Pseudodominance

The phenotypic expression of a recessive allele that occurs when the corresponding dominant allele on the homologous chromosome is lost via deletion.

Haploinsufficiency

A gene dosage effect occurring when a single functional wild-type allele is insufficient to produce a normal phenotype following deletion of the other allele.

Cri-du-chat Syndrome

A human disease caused by a deletion on the short arm of chromosome 5, resulting in a small head, distinctive cry, widely spaced eyes, round face, and intellectual disability.

Wolf-Hirschhorn Syndrome

A human disease caused by a deletion on the short arm of chromosome 4, resulting in a small head with a high forehead, wide nose, cleft lip and palate, and severe intellectual disability.

Williams-Beuren Syndrome

A human disorder caused by a deletion on the long arm of chromosome 7, characterized by distinctive facial features, heart defects, and mental impairment.

Prader-Willi Syndrome

A human disorder caused by a deletion on the long arm of chromosome 15, characterized by feeding difficulty at an early age, becoming obese after 1 year of age, and mild to moderate intellectual disability.

Duplication

A chromosomal mutation characterized by the presence of two copies of a specific chromosomal segment.

Inversion

A chromosomal mutation in which a segment of a chromosome is excised, turned 180 degrees, and reinserted.

Pericentric Inversion

An inversion that includes the centromere, which can alter the relative arm lengths and change an acrocentric chromosome into a metacentric chromosome.

Paracentric Inversion

An inversion that does not include the centromere, which leads to the formation of dicentric and acentric chromatids if crossing over occurs in an inversion loop.

Position Effect

An alteration in the level of gene expression or phenotypic outcome caused by moving a gene to a different chromosomal location or context.

Translocation

A structural chromosomal rearrangement involving the movement of a DNA segment between non-homologous chromosomes.

Balanced Translocation

A translocation event in which exchange occurs without any loss of DNA following the chromosome breaks, making a normal phenotype more likely.

Unbalanced Translocation

A translocation in which genetic material is deleted after the break occurs and before attachment takes place.

Robertsonian Translocation

A specific translocation involving the fusion of two acrocentric chromosomes (such as chromosomes 13, 14, 15, 21, and 22 in humans) to create one large metacentric chromosome and a small fragment that is often lost.

Ploidy

A term referring to the total number of complete chromosome sets present in a cell or organism.

Somy

A term referring to the number of copies of a particular individual chromosome present in a genome.

Polyploidy

The condition of possessing more than two complete sets of chromosomes within an organism.

Autopolyploid

A polyploid organism in which all chromosome sets originate from the same species and are completely homologous.

Allopolyploid

A polyploid organism resulting from the hybridization of two different species, containing homeologous chromosomes.

Homeologous Chromosomes

Partially homologous chromosomes derived from different parental species that often fail to pair properly during meiosis in an interspecific hybrid.

Unreduced Gametes

Gametes formed during meiosis that fail to undergo chromosome reduction, maintaining the somatic ploidy level ($2n$) rather than the normal haploid ($1n$) complement.

Endoreduplication

A mitotic event in which chromosomes replicate normally but the cell fails to undergo division, doubling the chromosome number.

Autotriploid

An autopolyploid organism possessing three sets of chromosomes ($3n$) that is characteristically sterile due to unbalanced chromosome segregation during Meiosis I (e.g., bananas, seedless watermelon).

Autotetraploid

A fertile autopolyploid organism possessing four sets of homologous chromosomes ($4n$) that is typically larger in size than related diploids (e.g., peanut, potato).

Amphidiploid

An allotetraploid ($4n$) organism produced when chromosome doubling via endoreduplication provides two copies of each chromosome, allowing normal pairing and restoring gametic fertility.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during anaphase of cell division.

Somatic Mosaicism

A condition resulting from nondisjunction during mitosis early in development, leading to an individual possessing two or more genetically distinct populations of somatic cells.

Turner Syndrome

A human sex-chromosome aneuploidy characterized by monosomy for the X chromosome ($XO$), resulting in a karyotype of $2n - 1 = 45$.

Klinefelter Syndrome

A human sex-chromosome aneuploidy characterized by disomy for the X chromosome ($XXY$), resulting in a karyotype of $2n + 1 = 47$.

Triple X Syndrome

A human sex-chromosome aneuploidy characterized by trisomy for the X chromosome ($XXX$), resulting in a karyotype of $2n + 1 = 47$.

Down Syndrome

A human autosomal aneuploidy characterized by trisomy for chromosome 21 ($2n + 1 = 47$), typically arising from nondisjunction during maternal gamete formation.

Familial Down Syndrome

A heritable form accounting for approximately 4% of Down syndrome cases, caused by the transmission of a Robertsonian translocation between chromosome 14 and chromosome 21.

Patau Syndrome

A human autosomal aneuploidy characterized by trisomy for chromosome 13 ($2n + 1 = 47$).

Edwards Syndrome

A human autosomal aneuploidy characterized by trisomy for chromosome 18 ($2n + 1 = 47$).