1.03 - Chromosomal Disorders Flashcards
What is a Chromosome?
It is a single piece of coiled DNA and chromatin containing many genes, regulatory elements and other nucleotide sequences
What is Ploidy?
Ploidy refers to the number of sets of chromosomes. E.g. Sex cells are haploid (n) and somatic cells are diploid (2n)
What is Euploidy?
The state of having a cell or organism with an integral multiple of the monoploid number. i.e. having an exact multiple of the haploid number. In humans, 2n=46 is euploidy
What is Aneuploidy?
State of not having euploidy. E.g. having an extra chromosome, or missing a chromosome.
What are imbalances in chromosome number usually lethal in utero?
Each chromosome contains hundreds of genes, the addition or loss of even a single chromosome disrupts the existing equilibrium in cells, and is in most cases, not compatible with life. However, a few exceptions exist.
What is trisomy 21?
An extra copy of chromosome 21 –> Down Syndrome.
What are the three types of Trisomy 21?
Trisomy 21: Develops from duplication of chromosome 21 in either sperm or egg.
Mosaic: Not all cells contain the extra chromosome. Caused by abnormal cell division after fertilisation
Translocation Trisomy 21: Part of chromosome 21 translocated to another chromosome. Patient has 45 chromosomes but all the genetic material
What are some symptoms of Down Syndrome?
Brachiocephaly, protruding tongue, small ears, upwards sloping palpebral fissures, almost shaped eyes. Atrial and ventricular septal defects, Lower IQ Reduced height Reduced life expectancy Increased chance of Alzheimers
Why is Aneuplody of sex chromosome much more tolerated than that in autosomes?
X inactivation (one of the X chromosomes is compacted to inactive state.
Small number of genes on the Y chromosome
Genes on the sex chromosome not required for survival
What are the two broad classes of structural chromosomal rearrangements?
Balanced (no net gain or loss of chromosomal material and no phenotype) and Unbalanced (net gain or loss of chromosomal material with a high chance of phenotype). The size of the rearrangement will often determine the symptoms/survival
What are the types of chromosomal rearrangements?
Deletions: part of a chromosome is removed
Duplications: Part of a chromosome is duplicated
Inversions: part of a chromes is reversed, end-on-end
Insertion/Translocation: Part of a chromosome is rearranged with a non-homologous chromosome
Describe the Chromosomal abnormality in Cri Du Chat syndrome.
Deletion of the short arm of chromosome 5p.
Patients have a distinct pitched cry due to congenital malformation of the larynx
Describe the chromosomal abnormality in Prader-Willi Syndrome
Deletion in chromosome 15 (q11-13)
Low muscles tone, short stature, chronic feeling of hunger and excessive eating –> obesity/diabetes
