Mitosis/Meiosis Flashcards
How many pairs of chromosomes do human cells contain?
23
Diploid cells
Cells which contain chromosomes in pairs.
In most organisms including humans are cells diploid/haploid?
Diploid
What does mitosis start with and result in?
One diploid cell to two identical diploid cells.
How is mitosis used?
For growth and repair. Also asexual reproduction.
Things that occur during interphase
- Energy stores increase
- Cells grow in size
- Organelles are replicated
- DNA is copied
Two main processes that occur in the mitotic phase.
Mitosis and cytokinesis
Mitosis
Division of the cell’s nucleus.
Cytokinesis
Division of the cell.
Chromosomes in interphase
Cannot be seen but are there, in the form of a dark material called chromatin.
What happens to chromosomes during interphase?
Replicated and become sister chromatids and are joined at the centromere.
Stages of Mitosis
Prophase, metaphase, anaphase and telophase.
What happens during prophase?
- Chromosomes condense and become visible.
- The nuclear membrane starts to break down.
- A pair of centrioles move to both poles of the cell.
- Proteins begin to form spindle fibres which attach to the centromere of each chromosome.
What happens during metaphase?
- The spindle apparatus completely forms.
- The chromosomes line up at the centre.
What happens in anaphase?
- The centromeres divide into two and spindle fibres begin to shorten. This pulls sister chromatids to opposite sides of the cell.
What happens in telophase?
- Spindle apparatus breaks down and nuclear membranes reform.
- Chromosomes uncoil back to their chromatin state.
How does cytokinesis work?
Central cell membrane is pulled inwards by the cytoskeleton. Eventually the membranes fuse to form two independent cells.
Why do centrioles not play a role in forming spindle fibres in plant cells?
They do not contain them.
Why and where does meiosis occur?
To produce gametes in sexual organs.
What does meiosis start and result with?
A diploid cell to four haploid cells.
Why are gametes still useful despite being haploid?
During fertilisation, they fuse together to form a zygote, combining chromosomes.
Gametes are genetically…?
Different
Both chromosomes in a homologous pair have exactly the same…?
Genes
If both chromosomes in a homologous pair have the same genes how is genetic variation created?
Different alleles can be inherited from each parent.
