Meiosis Flashcards
what are the 2 types of cell division?
mitosis and meiosis
what is mitosis
the division of somatic (body) cells. It produces
2 diploid cells (2n)
what is meiosis
the division of cells to produce gametes. It produces 4 haploid cells (n)
diploid vs haploid
Diploid cells have the full set of chromosomes (46 in humans) whereas haploid cells have a half set.
what are gametes, where are they produced?
Gametes are sex cells and they are produced in gonads.
gametes in plants vs animals
In animals: eggs and sperm, produced in ovaries & testes
In plants: the gametes are ovules and pollen
what is a homologous pair
Diploid cells have 2 chromosomes that contain the same genes. One was inherited from each parent. Such chromosomes are called homologous pairs.
how many homologous pairs do humans have?
Humans = 46 chromosomes = 23 pairs
22 homologous pairs of autosomes (non-sex chromosomes) and 1 pair of sex chromosomes.
what must happen before cell division and how does this occur?
Before cells divide, the chromosomes must replicate, or make another copy of themselves. They do this using the base-pairing rules. A & T, G & C
what happens when the chromosome replicates, what is each strand called and how are they held together?
The chromosome becomes double-stranded.
Each strand is called a chromatid and the chromatids are held together by a centromere.
what are the 5 stages of cell division and what occurs before?
Interphase
Prophase
Metaphase
Anaphase
Telophase
interphase
the chromosomes replicate
but are NOT visible
prophase 1
- chromosomes “wind up”
- nuclear membrane breaks
down - centrioles move to the poles
metaphase 1
- spindle fibres form
- chromosomes attach to
spindle fibres at the equator (middle)
in their homologous pairs (2 copies
of the same chromosome - one from each parent
anaphase 1
chromosomes move
to either end of the cell
telophase 1
- the original cell divides into 2
by the cell membrane pinching in
(cytokinesis) - the nuclear membrane may
reform
prophase 2
- if the nuclear membrane reformed, it again breaks down
metaphase 2
- chromosomes attach to the spindle fibres at the middle of the cell
(not in homologous pairs this time)
anaphase 2
- the chromosomes split and one
chromatid moves to each end of
the cell.
telophase 2
- each cell divides into 2 by cytokinesis
- the nuclear membranes reform
- the chromosomes “unwind”
- this all means that the original cell has produced 4 haploid daughter cells.
overview of the 8 steps in Meiosis
- Before meiosis starts, the parent cell replicates its DNA.
- The chromosomes then move to the centre of the cell.
- Homologous chromosomes are separated. This is an important step that does not happen in mitosis
- The cell membrane pinches the cell in half. Both daughter cells then enter a second round of division.
- Again, chromosomes move to the centre of the cells.
- This time sister chromatids are separated.
- The cell membrane pinches both cells in half.
how does meiosis relate to inheritance
Genetic variation is increased by meiosis. During fertilisation, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA.
IPMAT
Party
middle
apart
two
