Mitosis and meiosis

Question 1

What are the components of mitosis

Answer 1

• made up of interphase (G1,S,G2) and mitosis
• cells can exit cell cycle into G0
• cell cycle progression is tightly governed by checkpoints

Question 2

What happens during the phases of interphase (G1,S,G2)

Answer 2

G1: cell develops in size and develops normal physiological function of the cell
S phase: DNA replication
G2: resting period before mitosis

Question 3

What are the different functions of each checkpoint at interphase and mitosis

Answer 3

G1/S checkpoint
- checks for damage or gaps in DNA and repairs DNA before synthesis
G2/M checkpoint
- make sure DNA content is twice as much than at G1 checkpoint, and repair any damage
M checkpoint
- checking at metaphase plate each chromosome is engaged to a spindle fibre

Question 4

How does the cell prepare for mitosis

Answer 4

• centrioles duplicate in S phase
• nuclear envelope breaks down
• DNA condenses into mitotic chromosomes
  -centrioles migrate to opposite poles forming spindle fibres
• condensed chromosomes align with spindle fibres

Question 5

Whats the difference between chromosomes and centrioles

Answer 5

chromosomes - pairs
chromatids - individuals

Question 6

What are the changes to the chromosome during mitosis

Answer 6

interphase: chromosomes are extended and uncoiled forming chromatin

prophase: chromosomes coil up and condense, centrioles divide and move apart

prometaphase: chromosomes are in double structures, centrioles reach the opposite poles and spindle fibres form

metaphase: centromeres align on metaphase plate

anaphase: centromeres split and daughter chromosomes migrate to opposite poles

telophase: daughter chromosomes align on the metaphase plate

• daughter cells are genetically identical to parent cells

Question 7

What are the stages of meiosis

Answer 7

meiosis 1: prophase, metaphase, anaphase, telophase

meiosis 2: prophase, metaphase, anaphase, telophase

DNA replication occurs in S phase of interphase 1

Question 8

What are the five stages of prophase

Answer 8

i. Leptonema
- chromosomes condense and search for their homologous chromosome
ii. Zygonema
- loose pairing between homologous chromosomes (300nm apart) results in synaptonemal complex formation (no exchange of DNA in genetic recombination)
iii. Pachynema
- chromosomes approximately 100nm apart and non-sister chromatids ‘cross over’ exchanging genetic material
iv. Diplonema
- non-sister chromatids attempt to separate but are held together by chiasmata (tetrad) which must be resolved
v. Diakinesis
- spindles form and centromeres attach to tetrad

Question 9

What happens is meiosis

Answer 9

meiosis converts the diploid number (2n) to the haploid number (n) in gametes

2 chromosomes
the gametes are all genetically different
- genetic recombination occurs in meiosis 1