chromosomes and cell division, meiosis, chromosome abnormalities

Question 1

What does DNA ligase do?

Answer 1

ligates the fragments together

Question 2

Why do telomeres shorten?

Answer 2

due to ageing or stressors. When telomeres start shortening too much, can lead to problems in our body.

Question 3

What are the different stages in mitosis?

Answer 3

prophase
metaphase
anaphase
telophase
cytokinesis

Question 4

What happens in prophase?

Answer 4

Chromosomes condense
Nuclear membrane disappears
Spindle fibres form from the centriole

Question 5

What happens in metaphase?

Answer 5

Chromosomes aligned at the equator of the cell
Attached by fibre to each centriole
Maximum condensation of chromosome

Question 6

What happens in anaphase?

Answer 6

Sister chromatids separate at centromere
Separate longitudinally
Move to opposite ends of cell

Question 7

What happens in telophase?

Answer 7

New nuclear membranes form
Each cell contains 46 chromosomes (diploid)

Question 8

What happens in cytokinesis?

Answer 8

Cytoplasm separates
Two new daughter cells

Question 9

Give characteristics of centromeres?

Answer 9

Constricted region joining sister chromatids
Repetitive DNA sequences
Satellite DNA
Site of kinetochore
Protein complex that binds to microtubules
Required for chromosome separation during cell division

Question 10

Difference between heterochromatin and euchromatin?

Answer 10

heterochromatin so tightly stuck together that it won’t allow any of the machinery to actually get attached and do anything.
Genes are silenced.

Question 11

What are satellite, minisatellite, SINEs and LINES (long and short interspersed nuclear elements) for? {extragenic sequences in introns}

Answer 11

-Satellite DNA- extreme structural importance for our DNA and for chromosomes and lots of AT repeats
-Minisatellite DNA-

SINE and LINEs- serve a structural purpose and make up 45% of genome

Question 12

Describe the levels of how we go from DNA down into chromosome?

Answer 12

level 1 - nucleosome (one of beads on string)
level 2 - chromatin fibre (condensation by factor 40- beads on string forming solenoids - these bumped together)
level 3 - fibre-scaffold complex
level 4- chromosome

Question 13

What is the purpose of packaging DNA?

Answer 13

• DNA takes up less space
  -helps with managing and regulating how our genes are going to be activated
  -Inactive DNA can be folded into inaccessible locations until required
  -Inactive chromatin characterised by specific histone convalent modification (e.g. methylation)

Question 14

Which is the P and which is the Q arm?

Answer 14

p= petite and top arm
q= bottom arm

Question 15

Meaning of metacentric, sub-metacentric, acrocentric?

Answer 15

metacentric- centromere in middle
sub-metacentric- shorter p arm and standard q arm
acrocentric- really short p arm where so short its inactive

Question 16

What do we use to see centromeres?

Answer 16

fluorescent in situ hybridisation

Question 17

Where does mitosis happen?

Answer 17

only happens to our somatic cells

Question 18

What is process of meiosis?

Answer 18

used to make more sex cells

Question 19

What is the difference between meiosis and mitosis?

Answer 19

instead of two identical cells like mitosis, get four cells that have half of genetic info (haploid)

Question 20

Why do we get the genetic diversity?

Answer 20

crossing over
between prophase and metaphase 1 they cross over and exchange a part of their genetic material

Question 21

What happens in gametogenesis?

Answer 21

where meiosis happens, we make new gametes

Question 22

What is spermatogenesis?

Answer 22

create through meiosis 1 and 2 create 4 sperm cells

Question 23

Describe oogenesis?

Answer 23

start with first egg and then it matures into primary oocyte. Divides into a secondary oocyte and a polar body. Polar body has no role so gets flushed out. Secondary oocytes divide and creates one egg and three polar bodies.

Question 24

What determines if embryo is male or female?

Answer 24

whether sperm contains and x or y chromosome