Mitosis + Meiosis + Cell Cycle

Question 1

How many chromosomes are there in a human and how many of each type?

Answer 1

46 chromosomes
22 pairs of Autosomes (non sex chromosomes)
1 pair of sex chromosomes

Question 2

What are the male & female sex chromosomes?

Answer 2

Male- XY

Female- XX

Question 3

Where is DNA found?

Answer 3

In nucleus & mitochondria (a little bit & only maternal)

Question 4

What is the cell cycle for?

Answer 4

For all replicating cells

Question 5

What does each chromosome have?

Answer 5

A long arm (q) & a short arm (p) separated by a centromere

Question 6

What does mitosis produce?
What does the genetic info look like when a cell is not in replication, during & after?
What must the cell be in for mitosis to occur?

Answer 6

To produce 2 daughter cells, genetically identical to parent cells, growth & replace dead cells

Cell not in replication = chromatin
during = chromosomes
after = chromatids

Interphase

Question 7

What are the stages of interphase?

Answer 7

G1, S, G2

Question 8

What happens in G1, S & G2 phases of interphase?

Answer 8

G1- organelles replicate (DNA doesn’t yet) preparation
S- DNA replication
G2- preparation for mitosis

Question 9

What are the 2 checkpoints before mitosis occurs?

Answer 9

G1 checkpoint

G2 checkpoint

Question 10

What happens at each checkpoint & where is each checkpoint located in interphase?

Answer 10

G1 checkpoint (after G1 phase)
Checks for DNA damage pre DNA replication 
If there is damage, activates Tumour supressor gene p53 (activates p21, CAS uses cell autolysis to prevent tumour growth)

G2 checkpoint (after G2 phase)
Checks for DNA damage pre mitosis
Damaged bases removed by glycosylases enzymes

Question 11

What is the G0 phase?

Answer 11

Fully differentiated

Doesn’t replicate further

Question 12

What are the phases of mitosis?

Answer 12

Prophase, pro metaphase, metaphase, anaphase, telophase, cytokinesis

Question 13

What happens in prophase?

Answer 13

Chromatin condenses into chromosomes (visible)
Centrosomes nucleate Microtubules and move to opposite poles of nucleus
Centrioles form spindle

Question 14

What happens in prometaphase?

Answer 14

Nuclear membrane breaks down
Microtubules invade nuclear space
Chromatids attach to Microtubules 
Centromeres bind to spindle 
(Cell no longer has a nucleus)

Question 15

What happens in metaphase?

Answer 15

Chromosomes line up along equatorial plane

Question 16

What happens In anaphase?

Answer 16

Spindle fibers contract

Sister chromatids separate and pushed to opposite poles of the cell

Question 17

What happens in telophase?

Answer 17

Nuclear membrane reforms
Chromosomes unfold into chromatin (invisible)
2 nuclear envelopes form

Question 18

What happens in cytokinesis?

Answer 18

Division of cytoplasm

Form 2 genetically identical daughter cells, a nucleus with 46 chromosomes

Question 19

What does meiosis form?

Answer 19

4 haploid cells (23 chromosomes)
Genetically different/variation
2 cell divisions
Only in gametes

Question 20

What happens In meiosis I?

Answer 20

Chromosome number is halved
Becomes haploid
2 chromatid chromosomes
2n to n

Prophase I - crossing over
Metaphase I - independent segregation

Question 21

What happens In meiosis II?

Answer 21

Remains haploid
Sister chromatids separate
1 chromatid chromosome

Question 22

What are 2 meiotoc pathologies?

Answer 22

Non disjunction

Gonadal mosaicism

Question 23

What causes non disjunction?

Answer 23

Failure of chromosome pairs to separate in Meiosis 1 or sister chromatids to separate properly in meiosis 2

Can result in downs syndrome (non-disjunction at chromosome 21 resulting in trisomy 21), likelihood of this happening increases with age of both men and females

Can also result in monosomy (loss of a chromosome) - Turners syndrome, only 1 X chromosome.

Question 24

What causes gonadal mosaicism?

Answer 24

Healthy parent has a mutated Germline

Increased chance with age