Cytogenetics Flashcards
What are the steps of giemsa banding (g-banding)?
Chromosomes in metaphase treated with trypsin to break proteins. Then stained with giemsa solution. Dark and light bands on chromosomes viewable with microscope
What does FISH stand for and what is it used for?
Fluorescence in situ hybridization
To examine presence or absence of a particular DNA sequence
To evaluate organization of a chromosome or chromosomal region
What is x-chromosome inactivation?
In females only, one X is transcriptionally active and one is inactive
It occurs early in embryo. Generally random and fixed.
Will generally inactivate a mutated X-chromosome preferentially
What is a Barr body?
Inactive X chromosome - only seen in women
What is the mechanism of X-inactivation?
DNA methylation, histone modification, and a histone variant macro H2A
Inactivation center on long arm that contains gene XIST
What are the genetic significances of X inactivation?
Dose compensation
Mosaicism
What is mosaicism?
Both paternal and maternal Barr bodies
What are examples of genes on the Y chromosome?
SRY - codes for testis determining factor
AZF - related to sperm
What are the two types of chromosomal abnormalities?
Structural
Numerical
What is abnormal euploidy and two examples?
Abnormality in entire set of chromosomes
Triploidy
Tetraploidy
What is triploidy and how does it usually occur?
3 sets of chromosomes - very early death
Mostly from dispermy
What is aneuploidy?
Addition or deletion of one or more chromosomes
What are the common types of aneuploidy?
Monosomic - one chromosome missing its diploid (X)
Trisomic - one chromosome has extra in its diploid (XXX)
What are the results of autosomal aneuploidy?
Monosomies usually incompatible with life
Trisomies are seen, such as down syndrome
What are the results of sex chromosome aneuploidy?
More common and less severe than autosomal aneuploidy
