Flashcards in Lab 4 (chromosomes) Deck (24):
It is not a single chromosome, but thousands of aligned copies of a chromosome that are stacked up in a bundle.
How do Polytene chromosomes form?
Multiple rounds of chromosomal replication without separation of the sister chromatids or cytokinesis.
Dark bands vs light bands
Dark bands = transcriptionally INACTIVE
Light bands = transcriptionally ACTIVE
Describe the size of human chromosomes to the fly polytene chromosomes.
Polytene chromosomes are larger than human chromosomes. The diameter of the nucleus of the salivary gland cells of larva is 2 times bigger than the nucleus of human cells.
The polytene chromosomes appear to contain five long and one short arm radiating from a central point called chromocentre. It is formed by the fusion of centromeres of all the eight chromosomes found in the cell.
q = long arm
1 = region
2 = band
one or more INDIVIDUAL chromosomes are added or deleted
one or more complete SETS of chromosomes are added
Includes the centromere. (peri = around)
one inversion is in the p (small) arm and the other is in the q (long) arm.
It does NOT include the centromere. (para = next to)
And both breaks occur in one arm of the chromosome either p(small) or q(long)
Description symbol for: a male with an inversion on chromosome 10, with one breakpoint located in region 1, band 1 of the long arm, and the other breakpoint in region 2, band 1 of the long arm.
Type of inversion
46, XY, inv (10) (q11 q21)
Description symbol for: A male with a small duplication located on the long arm of chromosome 3 within region 1, band 3.
46, XY, dup (3) (q13)
Description symbol for: A male with an inversion on chromosome 5, with one breakpoint located in region 1, band 4 of the short arm, and the other breakpoint in region 2, band 1 of the long arm.
Type of inversion
46, XY, inv (5) (p14 q21)
Description symbol for: A female with Patau syndrome.
47, XX, +13
Description symbol for: A male with a reciprocal translocation involving chromosomes 2 and 6. The breakpoint on chromosome 2 is on the short arm, region 1, band 3. The breakpoint on chromosome 6 is on the long arm within region 2, band 2._
46, XY, t(2; 6), (p13; q22)
Step 1 to prepare Karyotype
1) A sample of blood is drawn WBC. Fetus --> amniocentesis or Chorionic Villus Sampling ( sampling of the chorionic villus (placental tissue) and testing it for chromosomal abnormalities)
Step 2 to prepare Karyotype
2) Culture cells and add COLCEMID (related to colchicine a drug that Treats and prevents gout attacks, gouty arthritis)
COLCEMID disrupts mitotic spindles and prevents completion of mitosis.
Step 3 to prepare Karyotype
3) Suspend cells in hypotonic solution. This causes the nuclei to swell to facilitate the spreading of chromosomes.
Step 4 to prepare Karyotype
4) the swollen cells are fixed, dropped into a slide and dried
Step 5 to prepare Karyotype
5) Stain the chromosomes to differentiate between dark and light bands
Step 6 to prepare Karyotype
6) Photograph the spread
Step 7 to prepare Karyotype
7) Cut them out and organize them in the standard way.