Chromosomal Abnormalities Flashcards
What staining leaves a recognizable pattern of bands?
Giemsa staining.
What is the p arm?
Short arm of chromosome.
What is the q arm?
Long arm of chromosome.
What do the dark areas (heterochromatin) on a karyotype mean?
Highly condensed, gene-poor, and transcriptionally silent,
What do the light areas (euchromatin) on a karyotype mean?
Less condensed, gene-rich, and more easily transcribed
What is aneuploidy?
Abnormal number of chromosomes (not a multiple of 23).
What is non disjunction?
Uneven number of chromosomes in meiosis daughter cells. Results in +1 or -1 leading to trisomy and monosomy.
Most common form of aneuploidy?
Sex chromosome aneuploidy.
Why is sex chromosome aneuploidy better tolerated?
X chromosome inactivation of extra x chromosomes and low gene content of Y chromosome.
Why if extra x chromosomes are inactivated does sex chromosome aneuploidy still have an effect?
Both X and Y chromosome have a pseudo autosomal region.
How would you write the karyotype of an individual with trisomy 21?
47 +21 or 47,XX +21
What is the main cause of trisomy 21?
Maternal meiosis.
What increases the risk of trisomy 21 massively?
Age of the mother.
Why is maternal meiosis the main cause of trisomy 21?
As woman age the chromatids in the gametes they were born with become less organised. In males, sperm cell are continually generated.
What is mosaicism?
Presence of two or more population of cells with different genotype.
How can sex chromosome aneuploidy be an example of mosaicisim?
X chromosome becomes inactivated during early development.
When does crossing over of chromatids occur?
Prophase I.
What causes unequal crossover of chromatids?
Misalignment of homologous chromosomes.
What can unequal crossover of chromatids cause?
Trinucleotide expansion.
What can unequal crossover of chromosomes lead to?
Duplication and deletion of genes.
If there is an unequal crossover of chromosomes but it is balanced what can result?
Carrier not affected but offspring can be affected. Offspring can be normal, balanced carrier or unbalanced (affected).
What does philadelphia chromosome lead to?
CML (Chronic myeloid leukemia).
What is philadelphia chromosome?
Chromosome 9 and 22 break and exchange portions.
What is a metacentric chromosome?
Short arm and long arm are the same length.
What is a submetacentric chromosome?
Short arm is shorter than long arm.
What is an acrocentric chromosome?
Short arm encodes no genes.
What is a Robertsonian translocation?
Two acrocentric chromosomes form one chromosome.
When does a Robertsonian translocation cause problems?
If its unbalanced. Can cause problems in offspring.
