Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities

Question 1

basic structure of linear chromosomes

Answer 1

regions of chromosome:
telomeres
centromere
heterochromatin
euchromatin

Question 2

the end-replication problem and how it is solved

Answer 2

primers need to be used when replicating DNA on the lagging strand. Most of these primers are replaced by DNA when they detach, however the very end primer is not able to be replaced, this means a short sequence of DNA is lost with each replication of DNA. To combat this telomeres exist at the end of chromosomes, they are repeating sequences that contain no genes. So instead of genetic material from genes being lost, non-functional DNA from telomeres is lost instead.

Question 3

euchromatin

Answer 3

• open structure, less dense

- active genes

Question 4

heterochromatin

Answer 4

• condensed structure

- silenced genes

Question 5

centromere

Answer 5

constricted region joining sister chromatids, formed of repetitive satallite DNA.

Question 6

kinetochore

Answer 6

protein complex that forms on centromere and allows the attachment of spindles

Question 7

extragenic sequences of DNA

Answer 7

• tendemly repeated sequences: satellite and minisatellite DNA.
• SINEs (short interspersed nuclear elements
• LINEs (long interspersed nuclear elements

Question 8

chromatin

Answer 8

DNA-protein complex

Question 9

packaging of DNA

Answer 9

1. DNA is wrapped around histone protein, forming nucleosomes.
2. These nucleosomes are wrapped up themselves, 6 per turn.
3. This structure is then wrapped again.
4. then again to form a chromosome

Question 10

purpose of packaging of DNA

Answer 10

• Negatively charged DNA neutralised by positive charged histone proteins
• DNA takes up less space
• Inactive DNA can be folded into inaccessible locations until required

Question 11

primary laboratory technique for chromosome number abnormalities

Answer 11

Fluorescent in situ hybridisation (FISH)

Question 12

types of FISH

Answer 12

• unique sequencing probes
• centromeric probes
• telomeric probes
• whole chromosome probes

Question 13

centromeric probe function

Answer 13

Useful for determining chromosome number

Question 14

Telomeric probe function

Answer 14

• Useful for detecting subtelomeric rearrangements

- Often present in children with unexplained mental retardation

Question 15

Whole chromosome probes function

Answer 15

Useful for detecting translocations and rearrangements

Question 16

sequence of events in meiosis I

Answer 16

prophase- homologous chromosomes condense and pair up.
metaphase- pair of homologous chromosomes line up on equator, spindle forms
anaphase- spindles contracts, separating pair
telophase-chromosomes are moved to opposite poles
cytokinesis

Question 17

sequence of events in meiosis II

Answer 17

similar to mitosis except cells are haploid to begin with.
prophase- chromosomes condense
metaphase- chromosomes line up on eqautor and spindle forms
anaphase- spindle contracts and sister chromatids are pulled apart
telophase- sister chromatids are dragged to opposite ends of the cell
cytokinesis

Question 18

what is satellite DNA?

Answer 18

large arrays of tandemly repeating DNA sequences.

found at centromeres and telomeres

Question 19

what is mini-satellite DNA?

Answer 19

short arrays of tandemly repeating DNA sequences.

used for DNA fingerprinting

Question 20

what are SINEs?

Answer 20

short interspersed nuclear elements, highly repeated short DNA sequences interspersed throughout the DNA

Question 21

what are LINEs?

Answer 21

long interspersed nuclear elements, highly repeated long DNA sequences interspersed throughout the DNA