C2 - Cell Division Flashcards
MITOSIS
What are the stages of the cell cycle?
Interphase (G1, S, G2)
Mitosis (PMAT)
What does PMAT in mitosis stand for?
Prophase
Metaphase
Anaphase
Telophase
What is G1 of the interphase during the cell cycle?
Growth phase
i.e mitochondria + chloroplasts replicate as they have their own DNA to copy
What is S of the interphase during the cell cycle?
- DNA réplication.
- Duplicates the centrosomes which help separate DNA during mitosis.
What is G2 of the interphase during the cell cycle?
2nd growth phase.
Synthesis of proteins and organelles
Begins to reorganize its contents in preparation for mitosis.
In what type of cells does mitosis occur?
Somatic (body cells)
NOT gamete cells
What is mitosis important for?
Growth
Asexual reproduction
Repair damaged tissue
Replace worn out cells
MITOSIS
What happens to chromatin during interphase
It duplicates itself
MITOSIS
What happens to chromatin during prophase
Coils up into chromosomes
What happens in mitosis
Nuclear division producing 2 g. identical daughter cells.
Each containing the same no. of chromosomes as parent nucleus.
MITOSIS
Describe what happens in prophase (longest of the 4 stages of mitosis)
(DNA already been replicated)
Chromosomes condense = visible as pairs of chromatids.
Centrioles move to opposite poles of nucleus + develop spindle apparatus.
Nucleolus + nuclear membrane break down + disappears.
== Pairs of chromatids are free in cytoplasm.
MITOSIS
Describe the chromosomes produced in prophase
1 chromosome has 2 g. identical chromatids held together by a centromere.
MITOSIS
Describe what happens in metaphase
(Nuclear membrane has disappeared)
Microtubules attach to centromeres = chromosomes align on equator of spindle.
MITOSIS
Describe what happens in anaphase
Attached microtubules (spindle fibres) contract = splitting centromeres in 2.
This pulls chromatids to opp. poles of cell, centromere 1st.
Chromatids now called DAUGHTER CHROMOSOMES.
MITOSIS
Describe what happens in telophase
Daughter chromosomes reach poles, uncoil + lengthen
Spindle fibres break down
Nucleolus + nuclear envelope re-form
Animal cells = cytokinesis
How do you calculate the mitotic index?
No. of cells in mitosis / Total no. of cells X 100
MITOSIS
What is the chromosome appearance + location for the interphase
DNA replicates
Chromatin
MITOSIS
What is the chromosome appearance + location for the prophase
Chromosomes coil up
MITOSIS
What is the chromosome appearance + location for the metaphase
Chromosomes line up along equator
MITOSIS
What is the chromosome appearance + location for the telophase
Chromosomes uncoil back into chromatin
MITOSIS
What is the chromosome appearance + location for cytokinesis
Chromatin
Cancer
Uncontrolled mitosis
Cancerous cells divide repeatedly w/ formation of a tumour
Thought to be initiated by gene mutations in oncogenes or tumour suppressor genes
What does meiosis do
Produces cells w/ 1 set of chromosomes (1 from each homologous pair) from 2 stages of cell division:
Meiosis I and II.
When does meiosis occur
During sexual reproduction:
1 Diploid cell divides to produce 4 haploid cells (gametes).
What is the purpose of meiosis?
To keep the chromosome no. constant from 1 generation to the next.
G. variation in gametes + the zygotes they produce. There are 2 ways this can happen:
- Crossing over during prophase 1.
- Independent assortment at metaphase 1 so daughter cells contain diff. comb. of maternal + paternal chromosomes OR at metaphase II so daughter cells have diff. combination of chromatids.
Describe the interphase of meiosis
Can’t see chromosomes.
DNA replicates
Chromosomes made of 2 identical molecules of DNA
More organelles are synthesised
Mit. + Chlo. replicate
High rate of ATP + protein synthesis
Can still see nuclear envelope + nucleolus
When does crossing over take place
In prophase 1 in meiosis.
Between non-sister chromatids in bivalent.
== Each chromatid may break + reconnect to another chromatid.
=== Recomb. of maternal + paternal gen. info.
Describe what happens in prophase 1 of meiosis
Chromosomes condense, coil + thicken = visible as 2 chromatids.
Centrioles move to opp. poles of cell.
SYNAPSIS + crossing over occurs. (Be able to explain these)
Describe what happens in metaphase 1 of meiosis
Spindle fibres attach to centromere + move whole chromosome to middle/equator of cell.
Homologous chromosomes aren’t found opposite each other so are arranged randomly either side of the cells equator. = G.VARIATION
Bivalents (pairs of chromosomes) arrange at equator of spindle. REMEMBER the pairs aren’t identical.
Describe what happens in anaphase 1 of meiosis
Spindle fibres shorten to pull centromeres to opp. poles of cell.
Whole chromosomes are pulled but still made of 2 chromatids.
Describe what happens in telophase 1 of meiosis
2 new nuclear envelopes reform.
Each nucleus contains 1/2 of original no. of chromosomes but still made of 2 chromatids.
= Chromoses g. diff. from those in original cell.
CYTOKINESIS occurs
What is each chromosome made up of?
A pair of chromatids
What does meiosis 2 do?
Separates the 2 chromatids.
Describe what happens in prophase 2 of meiosis
Chromatin condenses + chromosome becomes visible.
Centrioles replicate.
New spindle fibres form at 90o to 1st.
Nuclear envelope + nucleolus disappear.
Describe what happens in metaphase 2 of meiosis
Spindle fibres align chromosomes randomly on equator of spindle.
Again, intro. g. variation due to random assortment of chromatids at equator.
Describe what happens in anaphase 2 of meiosis
Microtubules contract + centromeres divide.
Chromatids are pulled to opp. poles of cell by attaches spindle fibres.
When separated produce chromosomes.
Describe what happens in telophase 2 of meiosis
Chromosomes ucoil = each new chromosome may be g. diff. from original one.
Nucelar envelope + nucleolus reappear.
Cytokinesis begins
== 4 HAPLOID CELLS
Define an oncogene
A gene w/ the pot. to cause cancer
In simple terms, what is the result fo meiosis I?
Homologous pairs of chromosomes have separated w/ 1 chromosome of each pair going into either of the 2 daughter cells.
Each daughter cell has only 1 of each homologous pair, so they contain 1/2 the no. of chromosomes of the parent nucleus
In simple terms, what is the result fo meiosis II?
Chromatids separate + 2 new haploid nuclei divide again == 4 haploid nuclei are formed from parent nucleus each containing 1/2 the no. of chromosomes.
Every gamete is genetically unique.
What’s the difference in prophase between meiosis 1 + meiosis 2
Follows DNA replication = M1 yes / M2 no
Cross over = M1 yes / M2 no
What’s the difference in metaphase between meiosis 1 + meiosis 2
M1 = Homologous pairs align either side of the equator
M2 = Chromosomes align on the equator
What’s the difference in anaphase between meiosis 1 + meiosis 2
M1 = Chromosomes separate
2 daughter cells
M2 = Chromatids separate
4 daughter cells
Compare mitosis + meiosis
MITOSIS vs. MEIOSIS
No. of divisions = 1 vs. 2
No. of daughter cells = 2 vs. 4
No. of chromosomes in daughter cells = Same as parent vs. 1/2 of parent
Chiasmata = Absent vs. Present
G. Cross over = None vs. In prophase 1
Independent assortment = None vs. In metaphase 1 + 2
Genetic composition = G. identical w/ parent cell + each other vs. G. different
Why is it not possible for an organism to have a diploid number lower than 2?
Diploid means a pair of each chromosome.
So meiosis wouldn’t be able to take place.
Also because haploid can’t be less than 1.
“Push down hard on the cover slip, but don’t push the cover slip sideways”.
Explain this instruction
Push hard = spread/squash tissue
Don’t push sideways = avoid breaking chromosomes.
Why did the biologist choose to do the experiment on 200 cells
To ensure a representative sample
State the name given to the exchange of segments of chromatids by breaking and rejoining
Crossing over
Genetic difference between sister + non-sister chromatids
Sister = 2 identical copies of a chromatid w/ same genes + alleles
Non-sister = 1 strand is from mother + the 1 from father.
Explain how a doctor would recognise which cells are in interphase when looking at tissue samples
Able to see nucleus as nuclear membrane wouldn’t have been broken down.
+
No chromosomes would be visible.
