Test 1: Chromosome

Question 1

Cytogenetics, karyotye
Karyology, karyogram/idiogram

Answer 1

Cytogenetics: study of chromosomes +structure as well mitotic division
Karyotype: # + appearance of chromosomes in nucleus of eu
Karyogram-study of a whole set of chromosomes and when rearranged in photomicrograph =karyogram/idiogram

Question 2

Staining of chromosomes

Answer 2

Giemsa rowanowsky
for cells in arrested dev = metaphase + prometaphase bc its when chromosomes are at the most condensed form
- uses colchine solution
(Usually uses WBC- easily divides+grows in tissue culture
Using G banding staining technique

Question 3

When chromosomes best seen

Answer 3

Chromosomes are super coils of DNA. Best seen during cell division when chromosomes are highly contracted and heterochromatin form.

Can see sister chromatin during S phase-DNA replication
- joined by primary constriction=centromere

Question 4

Centromere

Answer 4

Pinching in+narrowing of sister chromatid due to formation of kinetochore
Has hundreds of kilobase pairs of DNA + is responsible for movement of chromosomes during cell division

Question 5

Chromosome divided into what parts

Answer 5

P(short) and q (long) arms centromere=primary constriction and telomere=tip
Play a role in sealing strands at end of chromosome+maintains structural integrity
Has tandem repeats of TTAGGG seq

Satellites (stalk like appendages) which form nucleolus + contain multiple repeated copies of rRNA.

Secondary constriction=main body of chromosome. Also has nuclear organizing region NOR which are on satellite cells (multiple copies of gene for rRNA)

Question 6

Chromosome type + draw

Answer 6

Listed acc to position of centromere
- METACENTRIC: centromere is centrally and p and q have comparable sizes. In chromosome 1,3,19,20
- ACROCENTRIC:centromere at terminal end+ very short p arm. Has satellites (stalk like appendages).forms nucleolus and have NOR (w multiple repeated regions of genes for rRA). Also has segment = secondary contraction. 13-15,21,22 Y
- SUBMETACENTRIC- centromere is intermediate position=off centre where has shorter p arm and longer q arm. 2, 4-12,16-18, and X
- TELOCENTRIC: centromere at end of chromosomes and only has q arm. Not found in humans.

Question 7

Chromosomal classification in karyogram

Answer 7

A: 1-3; large metacentric but 2 is submetacentric
B: 4-5; large submetacentric
C: 6-12 and X; medium submetacentric
D: 13-15; medium acrocentric
E: 16-18; short submetacentric
F: 19-20; short metacentric
G: 21-22 Y; short acrocentric but Y is submetacentric

Question 8

Differences observed when testing chromosomes

Answer 8

1. absolute sizes of chromosomes. (can differ in size by 20 times in same genera of same family)
2. Position of centromere: due to translocation
3. Relative size of chromosome: from segmental interchange of unequal lengths (one chromosome exchanges genetic material w other-one loses +shorter other gains=unequal lengths)-can be balanced or unbalanced
4. Basic # of chromosome: from successive unequal translocations (rearrangement of parts between 2 non homo chromo). Which removed all essential genetic info
5. In number and position of satellites
6. In degree + distribution of heterochromatic regions

Question 9

X inactivation

Answer 9

After fertilization. Choose if maternal or paternal X -chromosome, and the one not chosen condenses as a Barr body. Then mitosis occurs.

XXXY= 2 barr bodies
XY=0

• Located on the tips of X+Y chromosome : PAR1 (short arm=p) +PAR2 (long arm=q)
• Refers to genes in X+Y that behave like autosomes during meiosis
• Usually sex chromosomes are non-homologous (differ in size). Autosomes are homologous pairs (same seq of genes) and they undergo cross over
• Therefore the pseudo-autosomal region/genes undergo crossing over

No x-inactivation + no x-linked inheritance ??