Chromosomal Abnormalities & Structure – Lecture Vocabulary

Vocabulary flashcards covering key terms related to chromosomal number abnormalities, structural rearrangements, specific human aneuploidy syndromes, and chromosome anatomy from the lecture notes.

Nondisjunction

A cell-division error in which chromosomes fail to separate during anaphase, leading to abnormal gametes.

Meiosis I Nondisjunction

Failure of homologous chromosomes to separate in the first meiotic division, producing two (n+1) and two (n-1) gametes.

Meiosis II Nondisjunction

Failure of sister chromatids to separate in the second meiotic division, producing one (n+1), one (n-1), and two normal (n) gametes.

Polyploidy

Presence of one or more complete extra sets of chromosomes; usually fatal in humans and most animals.

Aneuploidy

Having one extra or one missing chromosome rather than full sets; includes trisomy and monosomy.

Trisomy

Condition of having three copies of a particular chromosome in somatic cells.

Monosomy

Condition of having only one copy of a particular chromosome in somatic cells.

Turner Syndrome (X0)

Female aneuploidy (45,X); short stature, sterile, often reduced mental ability; ~1/2500 female births.

Klinefelter Syndrome (XXY)

Male aneuploidy (47,XXY); sterile, possible female secondary traits, treatable with testosterone; ~1/500 male births.

XYY Syndrome

Male aneuploidy (47,XYY); tall stature, severe acne, mild mental effects; usually fertile; ~1/1000 male births.

Triple X Syndrome (XXX)

Female aneuploidy (47,XXX); largely normal but more likely to be sterile or have XXY/XXX offspring; ~1/1000 female births.

Trisomy 21 (Down Syndrome)

Only common autosomal trisomy compatible with adulthood; characteristic facial features, intellectual disability, risk of leukemia & Alzheimer’s.

Cri du Chat Syndrome

Disorder caused by deletion of the short arm of chromosome 5; infant cry resembles a cat, severe intellectual disability, shortened lifespan.

Philadelphia Chromosome

Reciprocal translocation between chromosomes 9 and 22 associated with chronic myelogenous leukemia.

Reciprocal Translocation

Exchange of segments between two non-homologous chromosomes; may cause deletions or duplications.

Inversion

Chromosomal segment flips orientation within the same chromosome, possibly causing gene disruption.

Deletion

Loss of a chromosomal segment; larger deletions are usually lethal, smaller ones can cause syndromes like cri du chat.

Duplication

Repeated segment of DNA within a chromosome; supplies raw material for evolutionary innovation.

Fragile Site

Region of chromosome that is structurally weak, often rich in CGG/CGC repeats, prone to breakage.

Fragile X Syndrome

Trinucleotide (CGG) repeat disorder at a fragile site on the X chromosome causing intellectual disability, especially in males.

Autosomal Trisomy

Extra copy of an autosome; most types are lethal except some cases of chromosomes 13,15,18,21,22.

Barr Body

Inactivated X chromosome visible in somatic cells of females; XXX females have two Barr bodies.

Chromatid

One of two identical DNA strands of a chromosome joined at the centromere after replication.

Chromonema

Coiled threadlike structure within a chromatid consisting of two longitudinal strands.

Chromomere

Bead-like thickened region along a chromonema containing genes.

Centromere

Primary constriction of a chromosome where sister chromatids attach; site of kinetochore formation.

Satellite

Small chromosomal segment separated from the main body by a secondary constriction.

Telocentric Chromosome

Chromosome with centromere at the extreme end, producing only one arm.

Acrocentric Chromosome

Chromosome whose centromere is near one end, creating one long and one very short arm.

Sub-metacentric Chromosome

Chromosome with centromere slightly off center, giving unequal arms and an L shape.

Metacentric Chromosome

Chromosome with centromere in the middle, forming two equal arms and a V shape.

Anaphase

Stage of cell division where chromosomes (or chromatids) move toward opposite poles; errors here cause nondisjunction.

CGG Repeat Expansion

Increase in number of CGG trinucleotide repeats, characteristic of fragile X and other repeat disorders.