A brief summary of the stages of Meiosis, including important terminology and definitions, the differences between mitosis and meiosis, and abnormal meiosis.
MEIOSIS
Meiosis 1:
Reduction division that results in two cells
being formed each with half number of
chromosomes of the parent cell, i.e. the
haploid (n) number
Meiosis 2:
A copying division which involves the two
haploid cells formed, each dividing again by
mitosis to form 4 haploid cells
Crossing over: the mutual exchange of pieces
of chromosomes so that whole groups of genes
are swapped between maternal and paternal
chromosomes
Synapsis: process where replicated
homologous pairs of chromosomes
come together to form bivalents.
They swap away pieces of their inner
chromatids by breaking and reforming
their DNA while they are paired up
Chiasmata: the points of crossing over
where the chromatids break
in this way some genes from a maternal
chromatid change place with some
genes from a paternal chromatid, the
outer unchanged chromatids are called
parentals
Why is crossing over important?
Variation > unique combination of genes
Mutations > new genes introduced
, Proces Mitosis Meiosis
s
Where plants and animals in the Plants: sporangia of the sporophyte
development of a zygote to an generation, in the formation in the
embryo > then the cells continue spores
to divide to form a mature Animals: reproductive organs, the
organism testes and ovaries, in the formation of
Plants: meristemmatic tissue to the gametes
bring abouth growth
Animals: growing regions in the
bones, skin and damaged areas
Purpose Keep the number of Halve the number of chromosomes
chromosomes in the daughter i.e. the diploid number reduced to the
cells the same as the number of haploid number to prevent
chromosomes in the parent cell chromosome number doubling after
This cell division is involved in: fertilization
Development of an adult
organism
Form a single zygote
Growth and repair of tissues
Regeneration of body parts
Asexual reproduction
Differences involves one cell division Involves two cell divisions
Prophase: no bivalents & no cross Prophase 1: Bivalents formed and
over crossing over occurs
Metaphase: centromeres split Metaphase: centromeres do not split
Anaphase: chromatids of each Anaphase: chromosomes of each
chromosome move to opposite homologous pair move to opposite
poles of the cell poles of the cell
Two daughter cells are formed Four daughter cells are formed each
with the same number of with half the number of
chromosomes as the parent cell chromosomes as the parent cell
(usually diploid) (haploid)
Somatic cells are formed which Gametes are formed which are
are similar genetically to the genetically different to each other
parent cell and the parent cell
Similarities Both are types of cell division
The DNA of the parents cells is replicated in interphase before cell division
starts
In early prophase the chromosomes become short and fat and are visible as
two chromatids joined by a centromere
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