chapter 6

Centromere

A region of a chromosome to which spindle fibers attach during cell division; determines the characteristic shape of a chromosome.

Telomere

Short repeated DNA sequences located at each end of chromosomes.

Metacentric

Describes a chromosome that has a centrally placed centromere.

Submetacentric

Describes a chromosome whose centromere is placed closer to one end than the other.

Acrocentric

Describes a chromosome whose centromere is placed very close to, but not at, one end.

Sex chromosomes

Chromosomes involved in sex determination, specifically the X and Y chromosomes in humans.

Autosomes

Chromosomes other than the sex chromosomes, specifically chromosomes 1 to 22 in humans.

Karyotype

A complete set of chromosomes from a cell that has been photographed during cell division and arranged in a standard sequence.

Amniocentesis

A method of sampling the fluid surrounding the developing fetus, used to diagnose genetic and developmental disorders.

Chorionic villus sampling (CVS)

A method of sampling fetal chorionic cells to diagnose biochemical and cytogenetic defects, usually performed in early pregnancy.

Polyploidy

A chromosomal number that is a multiple of the normal haploid chromosome set.

Aneuploidy

A chromosomal number that is not an exact multiple of the haploid set.

Monosomy

A condition in which one member of a chromosomal pair is missing.

Trisomy

A condition in which one chromosome is present in three copies.

Triploidy

A chromosomal number that is three times the haploid number, having three copies of all chromosomes.

Tetraploidy

A chromosomal number that is four times the haploid number, having four copies of all chromosomes.

Nondisjunction

The failure of homologous chromosomes to properly separate during meiosis or mitosis.

Trisomy 21

Aneuploidy involving an extra copy of chromosome 21, resulting in Down syndrome.

Turner syndrome

A monosomy of the X chromosome (45,X) resulting in female sterility.

Klinefelter syndrome

Aneuploidy of the sex chromosomes involving the XXY chromosomal constitution.

XYY karyotype

Aneuploidy involving an XYY chromosome constitution.

Cri du chat syndrome

A deletion of the short arm of chromosome 5 associated with congenital malformations and a characteristic cry.

Uniparental disomy (UPD)

A condition in which both copies of a chromosome are inherited from one parent.

Fragile-X syndrome

An X chromosome that carries a gap at band q27, associated with intellectual disability in males.