Chromosomes and Cell Division

Question 1

What is the end replication problem?

Answer 1

through multiple generations, strands will get shorter

Question 2

What is the solution to the end replication problem?

Answer 2

telomerase

Question 3

What are centromeres?

Answer 3

• Protein complexes that bind to microtubules and are required during cell division
• They are the constricted region joining sister chromatids
• site of kinetochores
• repetitive SNA sequences- satellite DNA

Question 4

Hererochromatin vs Euchromatin

Answer 4

• Heterochromatins has a condensed structure and silenced genes
• Euchromatin has an open structure and active genes

Question 5

Describe the structure of chromatin.

Answer 5

• formed of DNA packaged histones
• histones have a positive charge, DNA negative
• 146 bp DNA wrapped around core of 8 histones= nucleosome
• further wrapping of nucleosomes
• form solenoid structure

Question 6

By what factor is DNA condensed by at metaphase?

Answer 6

10,000

Question 7

What is the purpose of packaging DNA?

Answer 7

• 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 8

What is colchine?

Answer 8

• a microtubule inhibitor

- it enriches the population of cells that are visible

Question 9

Metacentric

Answer 9

p length= q length

Question 10

Submetacentric

Answer 10

p length< q length

Question 11

acrocentric

Answer 11

p length «< q length

Question 12

What does FISH stand for?

Answer 12

Fluorescent in situ hybridisation

Question 13

What types of FISH probes are there?

Answer 13

• unique sequence probes
• centromeric probes (useful for determining chromosome number)
• telomeric probes (detecting subtelomeric rearrangements, often present in children wit unexplained mental retardation)
• whole chromosome probes (cocktail of probes, used with different dyes, spectral karyotype, detecting translocation and rearrangements)

Question 14

What is meiosis?

Answer 14

• cell division in germ cells
• diploid cells (in ovaries and testes) divide to form haploid cells)
• chromosomes are passed on as re-arranged (recombinant) copies which creates genetic diversity

Question 15

What is a defining event in sexual reproduction?

Answer 15

recombination between homologues

Question 16

What are the 2 forms of gametogenesis?

Answer 16

• oogenesis= process of egg formation

- spermatogenesis= process of sperm formation

Question 17

Why is there a greater chance of mutation in sperm than in eggs?

Answer 17

they go through more cell divisions

Question 18

How many sperm and eggs are produced in each cycle of gametogenesis?

Answer 18

• 4 sperm

- 1 egg + 3 polar bodies

Question 19

Describe fertilisation.

Answer 19

• two haploid cells form 1 diploid cell which develops into an embryo
• whether sperm contains an X or Y chromosome determines if the embryo is female or male
• embryo contains an assortment of genes from each original parent- more genetic diversity

Question 20

What is maternal inheritance?

Answer 20

mitochondria (and their DNA) come only from the mother via the egg

Question 21

When does X inactivation occur?

Answer 21

• In the zygote both X chromosomes are active

- In the early embryo random inactivation of one X occurs

Question 22

What are 2 tandemly repeated DNA extragenic sequences?

Answer 22

• satellite DNA

- microsatellite DNA

Question 23

What are 2 highly repeated interspersed DNA extragenic sequences?

Answer 23

-SINEs (short interspersed nuclear elements)

LINEs (long interspersed nuclear elements)