chapter 6

  • Centromere: A region of a chromosome to which spindle fibers attach during cell division. The location of a centromere gives a chromosome its characteristic shape.

  • 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. In humans, the X and y chromosomes are the sex chromosomes.

  • Autosomes: Chromosomes other than the sex chromosomes. In humans, chromosomes 1 to 22 are autosomes.

  • 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 by inserting a hollow needle and withdrawing suspended fetal cells and fluid; used in the diagnosing fetal genetic and developmental disorders; usually performed in the 16th week of pregnancy.

  • Chorionic villus sampling (CVS): A method of sampling fetal chorionic cells by inserting a catheter through the vagina or abdominal wall into the uterus. Used in diagnosing biochemical and cytogenetic defects in the embryo. Usually performed in the eighth or ninth week of 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; having one less than the diploid number (2n - 1)

  • Trisomy: A condition in which one chromosome is present in three copies, whereas all others are diploid; having one more than the diploid number (2n + 1)

  • Triploidy: A chromosomal number that is three times the haploid number, having three copies of all autosomes and three sex chromosomes.

  • Tetraploidy: A chromosomal number that is four times the haploid number, having four copies of all autosomes and four sex chromosomes.

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

  • Trisomy 21: Aneuploidy involving the presence of an extra copy of chromosome 21, resulting in Down syndrome.

  • Turner syndrome: A monosomy of the X chromosome (45,X) that results in female sterility.

  • Klinefelter syndrome: Aneuploidy of the sex chromosomes involving XXY chromosomal constitution.

  • XYY karyotype: Aneuploidy of the sex chromosomes involving an XYY chromosome constitution.

  • Cri du chat syndrome: A deletion of the short arm of chromosome 5 associated with an array of congenital malformations, the most characteristic of which is an infant cry that resembles a meowing cat.

  • 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, or break, at band q27; associated with intellectual disability in males.