Slides in this set
Describe, with the aid of diagrams and photographs, the behaviour of chromosomes during meiosis, and
the associated behaviour of the nuclear envelope, cell membrane and centrioles. (Names of the main
stages are expected, but not the subdivisions of prophase)
Meiosis produces gametes which need to be haploid
· Meiosis I is a reduction division separation of the homologous pair of
· Meiosis II is similar to mitosis with the separation of sister chromatids
· Four haploid cells are produced
In meiosis the chromosome number is halved
Prophase 1: The chromosomes are made up of two chromatids. The chromatin condenses and super coils which
means the chromosomes shorten and thicken. The chromosomes are in homologous pairs and form a bivalent. The non
sister chromatids wrap around each other and attach at the chiasmata. The nucleolus disappears and the nuclear
envelope breaks down/disintegrates. Spindle made of protein microtubules forms.
Metaphase 1: The chromosomes line up across the equator of the spindle and attach to spindle fibres at the
centromeres. Each member of the homologous pairs faces opposite poles. There are centrioles on each end.
Anaphase 1: Homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles. The
centromeres do not divide. The chiasmata separate and lengths of chromatids that have been crossed over will remain
with the chromatid. Exchange between non sister chromatids had occurred during cross over in prophase 1.
Telophase 1: Two nuclear envelopes form (in animal cells) around each set of chromosomes at each pole and the cell
divides by cytokinesis. There is a brief interphase and the chromosomes uncoil.
Prophase II: Centrioles replicate and move to poles. The nucleolus disappears and chromosomes condense and
spindles form. If a nuclear envelope has reformed it breaks down again.
Metaphase II: Chromosomes are lying on the equator of the cell. They are attached to spindle fibres at centromeres.
Anaphase II: Centromeres divide and chromatids move towards the pole by spindle fibres.
Telophase II: Nuclear envelopes reform around the haploid daughter nuclei. In animals the two cells divide into four
haploid cells. In plants who don't give a damn a tetrad or four haploid cells form.…read more
· Explain the purpose of meiosis and how
it differs from mitosis.
Mitosis produces the cells of the body.
When they split they produce identical cells
with a complete set of DNA. They are
exactly like their parents. It only has one
division and that leads to two cells.
Meiosis produces the gametes- the
reproductive cells. Meiosis goes through two
divisions, one in meiosis 1 and one in
meiosis 2. In the end, it results in four cells
and each cell only contains half of the
· What are gametes?
Gametes are reproductive cells that unite
during sexual reproduction to form a new
cell called a zygote.
· What do the terms diploid and haploid
Haploid is having a single set of unpaired
chromosomes. Diploid is containing two
complete sets of chromosomes.…read more