Chromosome Structure And Function Flashcards
At what position are sister chromatids held together?
The centromere.
Describe the levels of DNA packaging.
DNA double helix > “beads-on-a-string” form of chromatin > 30nm chromatin fibre of packed nucleosomes > chromosome in extended form > condensed form of chromosome
What is the point of the organisation of DNA into chromosomes?
The organisation of DNA into chromosomes ensures that all the DNA is efficiently packaged within the cell. This will also become important for the correct replication and segregation of DNA during cell division.
Describe 4 cases in which chromosome abnormalities may be important.
1) . Cases of recurrent miscarriage, or in patients with fertility problems.
2) . Many cases of spontaneous abortion will have chromosomal abnormalities.
3) . Some individuals will carry a chromosomal abnormality which doesn’t affect their health. However, they will have an increased risk of miscarriage or having a child with developmental problems.
4) . Cancer cells often have chromosomes with structural abnormalities. These may have prognostic or diagnostic significance.
Describe telomeres.
The telomeres are the structures at the ends of the chromosomes which help to maintain chromosomal stability and integrity. They consist of repeat DNA sequences (TTAGGG)n.
What happens if the telomere is lost?
If the telomere is lost, the chromosome becomes unstable which normally leads to cell death.
Because of the way DNA replication occurs, some repeats are lost during every round if cell division.
Germ cells express an enzyme known as telomerase, which restores the telomeres to their full length in these cells.
What is the short are if a chromosome referred to as?
The p arm.
What is the long arm of the chromosome referred to as?
The q arm.
The chromosomes are grouped into how many groups based in size and centromere location?
7 groups.
Autosomes are numbered from largest (1) to smallest except for one exception. What is this
Chromosome 21 is larger than chromosome 22.
What are chromosome maps called?
Ideograms.
What three features are usually used to identify chromosomes?
Length, position of the centromere, banding pattern.
What is the most common type of chromosome staining used?
Giemsa staining.
Describe how you might go about obtaining a G-banded chromosome sample.
Chromosome analysis relies on obtaining a sample of cells (usually from the blood, but other tissue can also be used) which are then cultured and stimulated to divide. The cells are then arrested during metaphase, which is when the chromosomes are at their most condensed and visible. At this stage they consist of two sister chromatids. The cells are then fixed, subjected to a brief digestion with trypsin, then treated with Giemsa stain.
What is the normal male karyotype?
46, XY
