Chromosomal Abnormalities Flashcards
What is meant by the karyotype?
It is the chromosome set of an individual species in terms of number and structure of chromosomes
How many chromosomes do humans have?
22 pairs of normal chromosomes, 1 pair of sex chromsomes
What is a nucleosome?
When the DNA is wrapped around the histone proteins
When nucleosomes condense, what is formed?
A chromatin fibre
What is formed when chromatin condenses?
Chromosome
How do very long DNA molecules fit into the cell?
The DNA is wrapped around histones, forming nucleosomes which are then coiled into the chromatin fibre which is then further condensed to fit into the chromosome
Which cells do not contain chromatin?
Red blood cells
During what phase of mitosis are chromsomes usually karyotypes and why?
During metaphase, as the chromosomes are less condensed
Which cells are commonly chosen to be karyotyped and why?
White blood cells as they easily enter into mitosis
What is the short arm of a chromosome called?
The p arm
What is the long arm of the chromosome called?
The q arm
What connects the p arm with the q arm?
A centromere
What is added when karotyping to prevent mitosis from progressing past the metaphase?
Colchicine
How are the chromosomes released from the cell?
During karyotyping, a hypotonic solution is added, which causes the cell to swell and burst, releasing all the chromosomes
What is used during karyotyping to fix the chromosomes in place on the glass slide?
Carnoys fluid
what is carnoys fluid?
A combination of acetic acid and ethanol used to fix the chromosomes in place
What are the tips of the chromosome called?
Telomere
What staining technique is used in karyotyping?
Giemsa staining
What does giemsa staining produce?
Banding patterns on the chromosomes
How are the bands on chromosomes numbered?
The bands closest to the centromere is 1, and they increase in number the further you get from the centromere
What do dark bands on the chromosomes represent?
Heterochromatin - this is where the DNA is wrapped more tightly around the histone proteins and is more condensed
What do light bands on chromosomes represent?
Euchromatin - where the DNA is not packed as tightly around the chromatin so it is more open
What is meant by metacentric chromosomes?
Where the p arm and the q arm are the same length
What are submetacentric chromosomes?
Where the p arm is shorter than the q arm
What is meant by acrocentric chromosomes?
Where the short p arms have been reduced to a stump and replaced by non-coding satellites
What type of translocation can acrocentric chromosomes undergo?
Robertsonian translocations
What is a robertsonian translocation?
Where there is translocation between two acrocentric chromosomes which results in the formation of one chromosome with normal lengthed arms, and one where the two satellite sections have combined = loss of chromosome
Which chromosomes do Robertsonian translocations usually occur in?
13, 14, 15, 21 and 22
What is meant by a de novo abnormality?
A chromosomal abnormality which is not inherited from the parents
During what stage does cross-over occur?
During prophase of meiosis 1
What is the purpose of meiosis?
To reduce the diploid number to haploid so that diploid zygotes can be formed
To ensure there is genetic variation amongst offspring