Chromosome and their abnormalities Flashcards
How long is DNA?
3x10^9 base pairs long (3bn)
What is the normal human karyotype?
46 chromosomes
(46XY or 46XX)
22 pairs of autosomes and 2 sex chromosomes
How can we prepare chromosomes to look at?
From: blood lymphocytes Bone marrow cells Skin fibroblasts Amniotic fluid cells Chorionic villus Fetal Blood Giemsa banding
What are G banding chromosomes?
G - Giesma (stain for chromosomes)
chromosome pairs identical in banding pattern
What may vary when looking at G banded chromosomes?
Size of heterochromatic blocks at the centromere
satellite regions
Y chromosome
what determines the banding pattern of chromosomes?
The banding pattern may vary depending on the length of the chromosome
What is the purpose of mitosis?
cell division - produces genetically identical full complement of DNA
Normal growth of organism and in wound healing
Why are microtubule targeting drugs important in cancer?
As they target the microtubules forming during tumour proliferation and hence prevent the cells from dividing
What is the function of meiosis?
Reduction division from 46 chromosomes to only 23 per gamete
Reassortment of genes
What is the basic mechanism of meiosis?
Each homologue replicates to give two chromatids
homologous pair
exchange of material between non-sister chromatids (crossing over / recombination)
What are Chiasmata?
sites of crossing over
Where does variation come from during meiosis?
Independent assortment of maternal and paternal chromosomes
Presence of crossing over exchanges between homologous chromosomes (recombination)
what happens during normal meiosis for a female?
the primary cell divides into 2 which splits into 2 cells each of 23 chromosomes where one has the mitochondria and will go one to form the oocyte but the other cell has little mitochondria and forms a polar body which will eventually be lost.
What are some sex differences in meiosis?
- In males all the cell division products develop into mature sperm
In females one division product gives the ovum. The remainder are lost as polar bodies. - In the male, meiosis, follows a long series of mitotic divisions which is completed when the spermatids develop into sperm.
In the female, meiosis starts very early in development- it is then arrested- and finishes only after fertilisation
What is chromosomal non-disjunctions?
where there is uneven distribution of chromosomes into the new cells resulting from a chromosome pair failing to separate.