Stages in mitosis and meiosis Flashcards
during interphase, each chromosome is copied to form _____
during interphase, each chromosome is copied to form two sister chromatids
Sister chromatids remain joined at the centromere
diagram of cell at the end of interphase
https://www.shutterstock.com/image-vector/interphase-cell-division-cycle-260nw-2065936799.jpg
state the four stages in mitosis in order
prophase
metaphase
anaphase
telophase
Describe what happens in prophase
The first stage of mitosis is called prophase.
During prophase, the chromosomes condense and become visible in the nucleus.
Each chromosome consists of two sister chromatids joined at the centromere
The nucleolus disappears and the nuclear membrane starts to break down
A pair of centrioles move to either side (or pole) of the cell)
Proteins begin to form spindle fibres, (from the centrioles) which attach to the centromere of each chromosome.
These spindle fibres start to move the chromosomes towards the centre of the cell
Describe what happens in metaphase
The second stage of mitosis is called metaphase.
At metaphase, the spindle apparatus has completely formed and the chromosomes are lined up at the centre (or equator) of the cell
Describe what happens during anaphase
Anaphase is the third stage of mitosis
In anaphase, the centromeres divide into two, and the spindle fibres begin to shorten.
This pulls the sister chromatids towards opposite poles of the cell
Describe what happens during telophase
The last stage of mitosis is called telophase
In Telophase, the chromatids have reached the poles of the cell.
They are now referred to as chromosomes again
The spindle apparatus breaks down and the nuclear membranes reform
The chromosomes uncoil back to their chromatin state.
The nucleolus also reappears in each nucleus
At this point, the cell has now finished nuclear division by mitosis and starts cytokinesis.
Describe what happens during cytokinesis
During cytokinesis, the central cell membrane is pulled inwards by the cytoskeleton.
This creates a groove or furrow (at each end of the cell) which gradually deepens.
Eventually, the membranes fuse to form two independent cells
At this stage, cell division by mitosis is finished
draw a diagram showing mitosis
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/f4e50e04-dc30-4492-9d11-ba633c9a7ba9/stages-of-mitosis.png
describe the stages of meiosis
describe how meiosis can lead to genetic variation
where does cell division meiosis take place
and how is this different to mitosis
Cell division by meiosis only takes place in sex organs
mitosis take place in virtually all cells
explain why cell division by meiosis only takes place in sex organs
Cell division by meiosis only takes place in sex organs
This is because cell division by meiosis is only ever used to produce gametes (sperm and egg cells in mammals, and pollen and eggs in plants)
In cell division by meiosis what do we start with and what do we end up with
In cell division by meiosis we start with a diploid cell and at the end we have four haploid gametes
In cell division by mitosis what do we start with and what do we end up with
In cell division by mitosis we start with a diploid cell and at the end we have two identical diploid cells
diploid cell - cell which has pairs of chromosomes
contains chromosomes in pairs - diploid cells
What do the products of meiosis contain
Products of meiosis - haploid gametes
These contain individual chromosomes and not pairs
Explain why it is important that gametes are haploid cells
It is important that gametes are haploid cells
This is because during fertilisation, gametes fuse together to produce a fertilised egg or zygote.
Because gametes are haploid, the zygote has the diploid number of chromosomes
zygotes have ______, while gametes have _____
zygote have diploid number of chromosomes (diploid cells), while gametes have a haploid number of chromosomes (are haploid)
What can be said about all of the gametes made by meiosis
All of the gametes made by meiosis are genetically different
describe the features of a homologous pair of chromosomes
Diploid cells contain chromosomes in pairs
e.g. chromosome 9 pair
One chromosome in a homologous pair comes from your mother and the other chromosome in a homologous pair comes from your father
Both chromosomes in a homologous pair have exactly the same genes, but may have different alleles since you can inherit different alleles from each parent
e.g. both copies of chromosome 9 have the gene which determines blood group
However you can inherit different alleles from each parent e.g. for blood group inherit A allele from mother and B allele from father
Explain why the gametes produced from cell division by meiosis are all genetically different
Before the nucleus divides by meiosis, all the chromosomes are copied in interphase
each chromosome is copied to form two sister chromatids
Sister chromatids remain joined at the centromere.
At an early stage in meiosis, the two chromosomes in a homologous pair come together.
The chromatids of the two chromosomes wrap around each other
This process is called crossing-over
The attached pair of chromosomes are called a bivalent
The points where the chromatids are joined are called chiasmata
Parts of the chromatids can break off and exchange between the homologous chromosomes. (process of crossing-over)
The maternal and paternal chromosomes have now exchanged DNA
These are now recombinant chromosomes
Because these chromosomes have exchanged DNA, that means that they can exchange alleles
after crossing-over it
means that the recombinant chromosomes, each contain one chromatid with one allele and one chromatid with another allele ( A and B)
Since chiasmata can form at multiple points. So a large number of alleles can be exchanged.
This exchange of alleles is a major source of genetic variation in meiosis
describe binary fission
Binary fission in prokaryotic cells involves:
- replication of the circular DNA and of plasmids
- division of the cytoplasm to produce two daughter cells, each
with a single copy of the circular DNA and a variable number
of copies of plasmids.
where does binary fission take place
binary fission takes place in prokaryotic organisms
is mitosis a controlled or uncontrolled process
mitosis is a controlled process
what can uncontrolled cell division lead to
. Uncontrolled cell division can lead
to the formation of tumours and of cancers
malignant tumour = cancer
benign tumour = not cancerous
how do many cancer treatments work
Many cancer
treatments are directed at controlling the rate of cell division.
do viruses undergo cell division
explain your answer
Being non-living, viruses do not undergo cell division
Following
injection of their nucleic acid, the infected host cell replicates the
virus particles.
