Chromosomes and Chromosomal Abnormalities Flashcards
What are aneuploidies?
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes (whole extra or missing chromosome)
What are reciprocal translations?
Reciprocal translocations are a transfer of genetic material between homologous chromosomes. These are most commonly balanced exchanges, such that no genetic material is lost and individuals are phenotypically normal
What are Robertsonian Translocations?
• Two acrocentric chromosomes stuck end to end
In a reciprocal translocation, two different chromosomes have exchanged segments with each other. In a Robertsonian translocation, an entire chromosome attaches to another at the centromere
What are insertions and deletions?
Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. Deletions are mutations in which a section of DNA is lost, or deleted
What are duplications?
Duplication is a type of mutation that involves the production of one or more copies of a gene or region of a chromosome
What are inversions?
An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself
(DEF -> FED)
How can we recognise different chromosomes?
- Banding pattern with specific stains
- Length
- Position of centromere
What are acrocentric chromosomes?
Acrocentric chromosomes have a centromere which is severely offset from the center leading to one very long and one very short section. (The short arm doesn’t really matter - satellite ribosomal genes, tRNAs etc)
What chromosomes are acrocentric?
Ch 13, 14, 15, 21 and 22.
What are the four different types of chromosome?
Metacentric
Submetacentric
Acrocentric
Telocentric
Name a chromosome change that causes disease
Unbalanced chromosome rearrangement
What is unbalanced chromosome rearrangement?
Balanced chromosome rearrangement
-All the chromosomal material is present
Unbalanced chromosome rearrangement
-Extra or missing chromosomal material. Usually 1 or 3 copies of some of the genome.
Having 1 or 3 copies of a part of your genome is developmentally bad news
What is nondisjunction?
When chromosomes fail to separate normally resulting in a gain or loss of chromosomes
What can nondisjunction result in?
Aneuploidy in cell lines
This is why nondisjunction birth defect rate increases with age
What happens in Trisomy of chromosome 21? (47 X-X/Y)
Down syndrome