the cell cycle

Question 1

the cell cycle and the phases that happen within it

Answer 1

G1 phase - replication
- protein synthesis
- size increases

S phase - DNA synthesis
- chromosomes replicated

G2 phase - energy store replaced
- protein synthesis
chromosomes repair
- size increases

mitotic phase + cytokinesis

Question 2

the process of mitosis and the cell cycle

Answer 2

interphase - chromosomes are not visible ONLY chromatin ( loose + open strands so DNA is accessible for transcription + translation
all 23 chromosomes replicate into sister chromatids joint by CENTROMERE

MITOTIC PAHSE
prophase - chromatin begins to condense, chromosomes are visible
nuclear membrane breaks down
centrioles move to polar end of cell where spindle fibres attach to centromere

metaphase - chromosomes line up at the equator of cell

anaphase - spindle fibres separate sister chromatids into two where each sister chromatid moves to opposite cell
spindle fibres shorten

telophase - chromatids at opposite ends
- spindle apparatus breaks down
- nuclear membranes reform
- chromosomes uncoil back to chromatin

CYTOKINESIS - central cell membrane pulled inwards by cytoskeleton
membranes fuse to form 2 new cells

Question 3

why do we undergo mitosis

Answer 3

-repairing of cells
- asexual reproduction

Question 4

how do cells start off and end in meiosis

Answer 4

1 diploid cell makes four haploid genetically different cells

Question 5

how are the gametes genetically different

Answer 5

by the process of crossing over
2 chromosomes of homologous pairs pair together. (called a bivalent)
chromatids wrap around each other

point where chromosomes meet is CHIASMATA

parts break off and exchange, forming RECOMBINANT CHROMOSOMES

Question 6

what is chiasmata and recombinant chromosomes and bivalent

Answer 6

chiasmata - point of where 2 mum + dad diploid chromatids meet up and exchange

recombinant chromosomes - new chromosomes with new allele combinations

bivalent - the two homologous chromosomes pairing up

Question 7

why are gametes create haploid

Answer 7

because zygotes are the fusing together of 2 haploid from mother and father

so then zygotes can have diploid number of chromosomes with mother and fathers

Question 8

the process of meiosis

Answer 8

interphase
organelles duplicate + diploid chromosomes of mum + dad homologous

p1 - chromosomes condense (supercoiling)
- crossing over occurs by a bivalent forming and chromosomes meeting at chiasmata, they wrap around
- nuclear membrane begins to disintegrate
-centriole moves to polar sides + spindle fibres form

M1 - pairs of diploids line up on equator

A1 spindle fibres shorten
- chromosomes move to polar sides of cell, recombinant chromosomes form

T1 - chromosomes at opposite ends
- nuclear membranes reform
- uncoiling - chromatin
cytokinesis - divides to two haploid cells

P2 - supercoiling - visible chromosomes
- nuclear membrane breaks down
- spindle fibres

M2- line up on equator of spindle fibres

A2 - centromere of each chromosome divides
- spindle fibres short
- chromatids on opposite ends

T2 - nuclear membranes reform
- uncoil to chromatin
cytokinesis - division

https://www.youtube.com/watch?v=Uyf03tEjdvE

Question 9

how does meiosis form genetic variation

Answer 9

• independent assortment
• crossing over