Cytogenetics Flashcards
Trisomy 18
Overview
Both meiosis and mitosis convert 4n content of DNA to 2n content how are these events different?
In mitosis the sister chromatids are identical when the 2 n state is reached
In meiosis the sister chromatids are identical when the 2n state is reached
The events are not different
(But the 2n content in mitosis are from both parents e.g. not identical)
Mitosis
Meiosis
Independent Assortment of Chromosomes
Crossing over in Meiosis
How many distinct human chromosomes are there?
23
24
46
47
48
24
Identify the Karyotype and the logic behind the numbering
Terminology
Banding patterns of Chromosomes
Other banding techniques
Autosomal Numbers
1-22
X, Y
Sex Chromosomes
p
short arm of chromosome, petit
q
Long arm of the chromosome
del
Deletion of chromosome material
der
Derivative, a structurally rearranged chromosome
Dup
Duplication of part of a chromosome
Ins
Insertion of DNA into a Chromosome
Inv
Inversion of DNA within a Chromosome
/
a designation to indicate mosaicism, two different types of cells within one individual
t
Translocation; the regions which are translocated are described after the t symbol
Ter
terminal or (pter, qter)
r
Ring Chromosome
+ or -
Placed before the chromosome number, additions or deletions of a whole chromosome
+ 21 means
+ 21 means a third copy of chromosome 21
46, XY
Normal Male Chromosome Constitution
47 XX, +21
Female with Trisomy 21
47, XY, +21/46 XY
Male who is a moasiac of trisomy 21 and normal cells
46, XY, del (4)(p14)
Male with deletion of short arm of chromosome 4 at the band 14
46, XX, Dup (5p)
A female with a duplication of the short arm of chromosome 5
46, XX, inv (3) (p21;q13)
Female with an inversion of chromosome 3 between band 21 on the short arm and band 13 on the long arm of the chromosome
46, X, r( X)
Female with one normal X chromosome and one X ring
Ploidy
The only viable monosomy…
X - Chromosome
If too many expressed genes often lead to miscarriage, why do xxx females come to term, often without any symptoms?
There are very few genes on the x chromosome
Different parts of each x chromosome are expressed
Only one x chromosome is expressed
One x chromosome is inactivated so the individuals are similar to xx women
Only one x chromosome is expressed (Lyon hypothesis) — they get inactivated as barr bodies.
What brings about Polyploidy?
What brings about aneuploidy?
Given the following karyotype: 47,XY, +19/46, XY
The patient is a female with down’s syndrome
The patient has Down’s syndrome
Non-dsjunction event occurred in meiosis
Non-Disjunction event occurred in mitosis
The patient inherited an extra chromosome from their mother
Non-Disjunction event occurred in mitosis (Mocaism is usually due to a non-disjunction in mitosis late in development)
Non-dsjunction event occurred in meiosis (All of the cells would show trisomy)
Draw out non-disjunction in the first and second meiotic division
Non-disjunction occurs more often in
Non-disjunction occurs more often in the eggs rather than the sperm.
Which Trisomy’s are compatible with life?
Only 13, 18, and 21
Which monosomies are compatible with life?
No autosomal monosomies are compatible wiht life
X monosomy can be
Draw Mitotic Non-Disjunction
Trisomy and Maternal Age
Major Aneuploidy Syndromes Compatible with Live Births
Structural Abnormalities in Chromosomes
More Structural Abnormalities
Translocations
Gametes in Recipricol Translocation
Given a reciprocal translocation between 3 and 21 in one parent, what percentage of conceptions will most likely come to term, assuming all means of segregation have an equal probability? Explain.
100
75
33
67
50
25
0
33
Gametes in Reciprocal Translocation Pt. 2
Robertsonian Translocation
Gametes in Robertsonian Translocation
Microdeletions
Prenatal Cytogenetics
Amniocentesis
Chorionic Villus Sampling
Cordocentesis
Non-Invasive Techniques
Quad Test
DNA Sequencing – Cell Free DNA
How would you prevent this from happening again?
The only things she can do to prevent this from reoccurring. Get cytogenetic to look to see if there is a trisomy if not 1% chance of re-occuring. If so there’s a 50% chance of reoccurring.
Summary
