0226 Chromosomal disorders Flashcards
What is a chromosome
Chromosomes are linear structures made up of tightly packed, coiled DNA and histones. They are found in the nucleus and carry genetic information
Humans carry 23 pairs of chromosomes. What is the name of the 1st 22 pairs and what are the final pairs called
1-22nd pair = autosomes23rd pair = sec chromosomes/gametes
Describe the structure of a chromosome
An ‘X’ shaped structure with a centromere at the centre of the ‘X’, 1 pair of short arms, 1 pair long arms and telomeres at the end
Broadly speaking, what are the 2 categories of error that can occur in human chromosomes
Errors in the number of chromosomes and errors in the structure of chromosomes
Define Aneuploidy
Aneuploidy = State of having a non-integral numher of chromosomes to the monoploid number
Define Euploidy
Euploidy = State of having an integral number of chromosomes to the monploid number
What are the terms given to a cell or organism that has 1n, 2n, 3n and 4n?
Haploid, Diploid. Triploid, Tetraploid
True or False - chromosomal abnormalities have similar survival rates across all 23 pairs of chromosomes
False. Some chromosome pairs are more tolerant of abnormalities (e.g. 13, 18, 21)
Why are imbalances in chromosome numbers usually lethal in utero?
As each chromosome contains hundreds of genes, the addition or loss of even a single chromosome disrupts the existing equilibrium in cells, and in most cases, is not compatible with life
What are some physical features of person with trisomy 21
Brachycephaly, protruding tongue, small ears, upward sloping palpebral fissures, Atrial and ventricular septal defects, common atrioventricular canal, reduced height
Which of the parents (maternal or paternal) have the biggest influence on the risk factors of trisomy 21 (down syndrome)
Maternal. As the age of the mother at delivery increases so does the incidence of trisomy 21. A carrier patients also have a much higher rate of incidence
At what stage during the cell cycle do most reproductive aneuploidy errors arise
During Meiosis 1
True or False - Aneuploidy of the sex chromosomes is more tolerated than extra autosomes
True
Why is aneuploidy of the sec chromosomes more common than aneuploidy of the autosomes
X inactivation - one of the x chromosomes is compacted and inactivated. Also there is a small number of genes on the Y chromosomes and they are not required for survival
`What are the 5 types of chromosomal rearrangements? Which of these a single chromosome changes and which of these are paired
Single - Deletion, duplication, inversionPaired - insertion, translocation
What is the definition of balanced and unbalanced structural chromosomal changes
Balanced changes = no net gain or loss of chromosomal material and no therefore no phenotypeUnbalanced changes = net gain or loss in chromosomal material and therefore a high chance of phenotype
True of False - The size/magnitude of chromosomal rearrangement is inversely correlated to survival (i.e. bigger changes = less chance of survival)
True
After which stage of the cell cycle do structural chromosomal changes occur in paired chromosomes
In meiosis during prophase 1
Give two examples of diseases that could occur as a result of deletion of a chromosome
Cri Du Chat syndrome and prader-willi syndrome
