Variation in Chromosome Structure and Number

Vocabulary flashcards covering chromosome structure variations (centromeric positions, banding, deletions, duplications, inversions, translocations) and chromosome number alterations (euploidy, aneuploidy, autosomal and sex chromosome syndromes).

Metacentric

describes a chromosome with the centromere near the middle

Submetacentric

A chromosome whose centromere is located off-center, producing a distinctly shorter short arm ($p$) and a longer long arm ($q$).

Acrocentric

A chromosome whose centromere is located significantly close to one end, resulting in a very short $p$ arm.

Telocentric

A chromosome whose centromere is located at or near the terminal end, resulting in an essentially nonexistent $p$ arm.

p arm

The short arm of a eukaryotic chromosome located on one side of the centromere.

q arm

The long arm of a eukaryotic chromosome located on the opposite side of the centromere from the $p$ arm.

G bands

Alternating dark and light bands produced by Giemsa staining of chromosomes, which follow a conventional numbering system to map locations on metaphase and prometaphase chromosomes.

Terminal deletion

deletion in which a segment is lost from the end of a linear chromosome

Interstitial deletion

deletion in which an internal segment is lost from a linear chromosome

Cri-du-chat syndrome

A human genetic disorder occurring in individuals who are heterozygous for a deletion on the short arm of chromosome 5.

Chromosomal duplication

the repetition of a segment of DNA more than once within a chromosome and/or within a genome

Chromosomal inversion

a change in the orientation of genetic material along a chromosome such that a segment is flipped or reversed from the normal order

Simple translocation

A structural rearrangement in which a single piece of one chromosome breaks off and attaches to a non-homologous chromosome.

Reciprocal translocation

A two-way chromosomal exchange where two non-homologous chromosomes break and exchange genetic segments.

Misaligned crossing over

An aberrant crossover event between misaligned homologous chromosomes during meiosis, resulting in one chromosome bearing a duplication and the other bearing a deletion.

Paralogs

two or more homologous genes that are found within a single species and constitute a gene family.

Globin gene family

An evolutionary gene family originating from an ancestral globin gene that duplicated and diverged into myoglobins and hemoglobin subunit clusters ($\alpha$ chains and $\beta$ chains).

Euploidy

describes an organism in which the chromosome number is an exact multiple of a chromosome set (e.g., diploid $2n$, triploid $3n$, tetraploid $4n$).

Polyploidy

An alteration in chromosome number in which an organism possesses three or more complete sets of chromosomes, such as triploidy ($3n$) or tetraploidy ($4n$).

Aneuploidy

A variation in chromosome number involving an alteration in the count of specific individual chromosomes within a set rather than entire sets (e.g., $2n+1$ or $2n-1$).

Trisomy

An aneuploid condition in which a diploid organism has three copies of a particular chromosome ($2n + 1$), resulting in a 150% level of gene expression for that chromosome.

Monosomy

An aneuploid condition in which a diploid organism possesses only one copy of a specific chromosome ($2n - 1$), resulting in a 50% level of gene expression for that chromosome.

Patau syndrome

An autosomal aneuploid condition caused by Trisomy 13 (frequency $1/15{,}000$), characterized by mental and physical deficiencies, a wide variety of defects in organs, a large triangular nose, and early death.