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Meiosis - Coggle Diagram
Meiosis
Meiosis: Reduction Division
The process of meiosis
Meiosis & sexual reproduction
Diploid
cell (2n) has
2 complete sets
of
paired
chromosomes, 1 from each parent
Haploid
cell (n) has a
single set
of
unpaired
chromosomes
During meiosis, a
single diploid
cell
divides & produces haploid
reproductive cells
Meiosis is
important
in sexual reproduction because it involves
combining
genetic info of 1 parent with that of the other parent to
produce
a genetically unique individual
Stages of meiosis
Homologous chromosomes
Every cell as 2 of each chromosome -
homologous pair
They are similar in
shape, position & info
, but
not identical
to each other
One
chromosome in
each pair
is from the mother, the other from the father
Paternal & maternal
chromosomes may carry
different versions
of the
same gene
, e.g. the gene for eye colour may be different
Sister chromatids are
from the same
chromosome,
replicated
DNA
connected together
at the
centromere
Meiosis l
Diagram only
Meiosis ll
Diagram only
The
phases
in
meiosis ll
are the
same
as in
mitosis
Purposes of reduction division
Production of gametes
Gametes are
produced from
germ cells in the
ovary & testes
The
production
of gametes is known as
gametogenesis
Male
sex cells are
produced
by
spermatogenesis
Female
sex cells are
produced
by
oogenesis
Alternation of generations
In some species organisms alternate between a haploid & diploid from during its life cycle
There's an alternation of generations in life cycles of protists, fungi, mosses, ferns, gymnosperms & angiosperms
Each phase involves one or two organisms or body forms:
A haploid gametophyte
A diploid sporophyte
The Importance of meiosis
The number of chromosomes found in an organism is known as its
Ploidy
Each species has a different number of chromosome number making up its genome
During meiosis, the
2n
chromosome number is halved to
n
Its useful when producing gametes because when they combine during fertilization, the diploid number is restored & maintained
Cells produced during meiosis are genetically different, resulting in greater variety in species, which allows the species to show adaptation
Meiosis allows for alternation of generations in organisms
Introducing genetic variation
Factors:
Chiasmata formation / crossing over
The process when 2 original sets of chromosomes in cell can
exchange sections
of DNA when they lie next to each other,
during
meiotic reduction division process
Gamete fertilization
During
sexual reproduction, fertilization of gametes introduces a
different set
of chromosomes
from different
organism of
same
species
Random segregation
germ
cell is an
embryonic
cell that can
develop into gamete
- either a
sperm
or an
ovum
During
meiosis & production of gametes the diploid set of chromosomes is
randomly mixed
&
separated
It produces
different combinations
of genes
from
the chromosomes in germ cell
Consequences of abnormal meiosis
Down Syndrome
When people have
somatic (body) cells
with 47 chromosomes - an extra chromosome 21
The chromosome of pair number 21
fails to separate
& the one gamete will have an extra chromosome
If this gamete
fertilizes with
normal gamete, the child will have
3
chromosomes
on pair 21
Most frequent aneuploidy in
newborns
,
due to
incomplete chromosome separation (non-disjunction) in meiosis
A few mitotic errors
can cause
Trisomy 21
Trisomy commonly happens in the
first maternal
meiotic division, but some disjunctions
occur in second division
, during development of embryo
Meiotic process is
sensitive to
effects of poisonous endogenous & exogenous (internal & external) factors like nuclear radiation
Environmental factors
can cause
aneuploidy during meiosis
Meiosis
can result
in incomplete chromosome separation (meiotic arrest), or aneuploid spermatozoa & ova
These meiotic disorders
can cause
male infertility, spontaneous abortions &
can affect
offspring
Aneuploidy
occurs in
humans when
more
than a diploid set of chromosomes is
found
making up the
genome
Abnormal meiosis
leads to
disorders
Meiosis & Mitosis: Similarities & Differences
Mitosis: the process of cell replication
Stages of mitosis
Diagram only
Similarities
DNA replication occurs in mitosis & meiosis during interphase
Nucleolus & nuclear membrane break down during prophase of mitosis & meiosis
Spindle fibre forms during prophase of mitosis & meiosis
Chromosomes line up at the equator during metaphase of mitosis & meiosis
Spindle fibre contracts during anaphase of mitosis & meiosis
Mitosis & meiosis involve cargokinesis first, followed by cytokinesis
Differences
Diagram only