Karyotyping Flashcards
What is karyotyping?
Determination of a karyotype - arrangement of chromosomes by size and appearance to determine any chromosomal abnormalities
What is largest chromosome?
1 - comprises 10% of total length of DNA in cell
How is each pair of chromosomes distinguished?
By its individual banding pattern
What is most popular type of banding?
G-banding
What is purpose of G-banding?
To produce a visibile karyotype by staining condensed chromosomes (metaphase chromosomes)
What are metaphase chromosomes treated with and why?
Trypsin - to partially digest the chromosomes
What are the treated chromosomes then stained with in G-banding?
Giemsa stain
How are pattern of bands numbered?
On each arm of the chromosome from the centromere to the telomere
What are the results of G-banding?
Heterochromatic regions stain more darkly
Less condensed chromatin stain as light bands
The less condensed the chromosomes are, the more bands appear
What are heterochromatic regions?
AT-rich and gene-poor
What are less condensed chromatins?
GC-rich and more transcriptionally active
What cells are required for karyotyping?
Actively dividing cells (bone marrow, tumours, lymph nodes, chorionic villi etc) either grown in tissue culture or extracted from tumours
Some observations are carried out on B lymphocytes. What is required here?
Special techniques needed as not normally dividing spontaneously
Why are chromosomes derived from blood lymphocytes ideal?
Can be analysed 3 days after they are cultured
What are lymphocytes induced to proliferate using?
A mitogen (stimulates mitosis)
Skin fibroblasts, bone marrow cells, chorionic villus cells tumour cells or amniocytes can be used, but what is the difference?
Can require up to 2 weeks to obtain sufficient amount of cells for analysis
