Chromosomal Aberrations Quiz

Study Notes

Euploidy: Normal chromosome number for a species (humans: 46 in somatic cells, 23 in gametes)
Polyploidy: Chromosome number is a multiple of the haploid set
- Triploidy: 3 copies of each chromosome (69 chromosomes total). Often results in miscarriage. Can be caused by fertilization of an egg by two sperm (dispermy) or failure in a meiotic division in the egg or sperm.
- Tetraploidy: 4 copies of each chromosome (92 chromosomes total). Extremely rare and almost always lethal, caused by failure of the first zygotic division.
Aneuploidy: Abnormal chromosome number due to an extra or missing chromosome, not affecting the entire set of chromosomes
- Trisomy: Presence of three copies of an autosome or sex chromosome (e.g., Down syndrome). The karyotype is described as (47,XY,+21).
- Monosomy: Absence of a single chromosome. Monosomy of an autosome is often incompatible with life. The only known live birth example is Turner syndrome (45, X)

Presence of two or more genetically different cell lineages within one individual
- Mosaicism: Genetically different cells arise from the same zygote
- Chimerism: Fusion of two different zygotes occurs

Involve chromosome breakage and rejoining in an atypical configuration
Balanced Rearrangements: Chromosome complement is complete; no loss or gain of genetic material (generally harmless unless a breakpoint affects a critical gene)
- Examples: Inversions, insertions, reciprocal translocations (exchange of segments between non-homologous chromosomes) and Robertsonian translocation (fusion of two acrocentric chromosomes)
Unbalanced Rearrangements: Chromosome complement has an incorrect amount of material (Often serious clinical consequences)
- Examples: Deletions (loss of chromosomal material), Duplications (extra copies of chromosomal material).

Deletions: Loss of part of a chromosome. Loss of more than a few percent of the genome is often lethal
Inversions: A segment of a chromosome is reversed. Balanced rearrangements, usually not harmful unless a breakpoint affects a critical gene.
Insertions: Insertion of a segment of one chromosome into another.
- Will be balanced if the inserted material has moved from elsewhere in a different chromosome
- Will be unbalanced if the inserted material has come from some other chromosomal location
Duplications: Extra copies of chromosomal material.
Translocations: Transfer of genetic material from one chromosome to another. - Reciprocal Translocations: Exchanging segments between non-homologous chromosomes - Robertsonian Translocations: Two acrocentric chromosomes fuse; short arms are often lost, but overall number of chromosomes is decreased
Isochromosomes: Result from an abnormal centromeric division; consisting of two identical arms (q-arms or p-arms)
Ring Chromosomes: A chromosome that forms a ring shape due to breaks and rejoining. Often involves loss of material at the ends resulting in potentially serious consequences.