Chromosomes and Abnormalities Flashcards
How many pairs of chromosomes?
46 chromosomes
22 autosomal pairs
1 pair of sex chromosomes XX or XY
What cell types can be cultured to test for cytogenetics?
- Blood – T-lymphocytes
- Skin / Umbilical cord / Placenta
- Bone marrow
- Solid tumour
- Amniotic fluid / Chorionic villus - Prenatal
How are cell samples put into the process of karyotyping?
- Place sample in culture medium containing PHA
- Incubate for 48-72 hours
- Add colcemid - inhibits spindle formation, stops cells at metaphase to see condensed chromosomes
- Add hypotonic solution - cells swell
- Cells dropped and fixed onto slide to spread
- Slides are then treated with trypsin to digest proteins and giemsa to produce g banding on chromosomes
- Slides are scanned, analysed in software.
How are the regions numbered on chromomes?
Regions increase from centromere outwards.
What is the ISCN for a normal female and normal male?
46,XX
46,XY
Two types of chromosomes abnormalities:
Numerical, structural
Two types of chromosomes abnormalities:
Numerical, structural
Name 3 numerical chromosome abnormalities with ISCN:
Trisomy - Extra chromosomes at 21, Downs syndrome
47,XX,+21
Monosomy - Loss of a chromosome, Turner syndrome
45, X
Polyploidy - 3 whole sets of chromosomes, 69 XXY
Name the 4 structural chromosome abnormalities with ISCN:
Translocation - Exchange of material
Inversion - Changing of orientation, no loss or gain of material
Duplication - Gain of material
Deletion - Loss of material
ISCN ?
What is non disjunction and where does it occur?
When the chromosome doesn’t separate properly in meiosis.
Occurs in meiosis 1 and meiosis 2
How does non disjunction affect meiosis 1?
Results in - 2 disomic gametes + 2 nullisomic gametes
How does non disjunction affect meiosis 2?
Results in - 1 disomic gametes,
1 nullisomic gametes,
2 normal gametes
How does disomic gamete and nullisomic gamete affect conceptus?
Disomic - Leads to trisomy
Nullisomic - Leads to monosomy
Edwards syndrome karyotype?
47,XX,+18
Patau syndrome karyotype:
47,XX,+13