MEIOSIS NOTES
MEIOSIS NOTES
Asexual Reproduction
•
form of duplication using only mitosis.
Advantages:
•
produces only genetically identical offspring
called
clones
•
it is rapid, allowing for quick spread of an
organism
•
Produces twice as many offspring
Disadvantages:
•
Doesn’t allow for variation from one generation to
another
•
Based on amount of food available
Examples: plant cuttings, Amoeba, bacteria,
Sexual Reproduction
•
Form of reproduction where a new individual is
created by fusing two haploid cells (
fertilization
)
•
Zygote
– cell created when sperm and egg unite
–
contains two sets of chromosomes
Advantage: Allows for genetic variation
Offspring look different than parents
Disadvantage: slower reproduction rate
less reliable
more time/energy
Ex. Humans, animals
Differences between meiosis and
mitosis? (Picture shows meiosis)
What does meiosis do?
•
1) Meiosis takes a cell with two copies of every
chromosome (diploid) and makes cells with a
single copy of every chromosome (haploid).
•
This is a good idea if you’re going to combine two
cells to make a new organism. This trick is
accomplished by halving chromosome number.
•
In meiosis, one diploid cells produces four
haploid cells.
•
Meiosis is necessary to halve the number
of chromosomes going into the sex cells
Why halve the chromosomes in gametes?
•
At fertilization the male and female sex
cells will provide ½ of the chromosomes
each – so the offspring has genes from
both parents
What else meiosis does…
•
2) Meiosis scrambles the specific forms of
each gene that each sex cell (egg or sperm)
receives.
•
This makes for a lot of genetic diversity. This
trick is accomplished through
independent
assortment and crossing-over.
•
Genetic diversity is important for the
evolution of populations and species
.
Meiosis
converts a diploid cell into a haploid
gamete.
•
Before meiosis, cell goes through Interphase,
duplicating its chromosomes
•
The result is two genetically identical sister
The result is two genetically identical sister
chromatids
chromatids
which remain attached at their
which remain attached at their
centromeres
centromeres
(different than mitosis)
(different than mitosis)
Meiosis I
•
Prophase I : chromatid
pairs pair up with
their homologous pair,
forming a
tetrad
(two
chromosomes
on four chromatids)
Meiosis I
•
Prophase I : chromatid
pairs pair up with their
homologous pair,
forming a
tetrad.
•
Crossing over -
pieces of
two homologous
chromosomes, switch
places and end up on
the other chromosome
•
allows for genetic
diversity (called genetic
recombination)
•
Metaphase I : Tetrads line up
along the center.
–
Independent assortment
–
homologous chromosomes line
up randomly
•
Anaphase I : tetrads split and
move in opposite directions.
•
Telophase I/Cytokinesis: Two
cells form. End product of
Meiosis I is two haploid (n)
cells.
Meiosis I
Meiosis II
•
Prophase II : chromatid pairs
move toward the center
•
Metaphase II : The chromatid
pairs line up along the center of
the cell.
•
Anaphase II : The chromatid
pairs split moving the individual
chromosomes toward the
opposite poles.
•
Telophase II/Cytokinesis : Each
of the two cells splits. All are
haploid
•
The haploid cells may develop into gametes.
In most male animals, all four cells develop
into
sperm
. In females, one develops into an
ootid (egg cell)
, and three into
polar bodies
.
Fertilization
•
When the gametes combine (sperm + egg),
fertilization occurs. This restores the human
chromosome number back to 46.
•
Remember prior to this event each sperm had
23, and the egg had 23.
•
The product is called a zygote.
•
Why is fertilization important?
–
To join to gametes which starts a new life.
This resource explores the differences between asexual and sexual reproduction, highlighting the advantages and disadvantages of each method. It also delves into the processes of meiosis and mitosis, emphasizing their roles in producing genetic diversity and ensuring proper chromosome distribution in gametes.
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Presentation Transcript
Asexual Reproduction form of duplication using only mitosis. Advantages: produces only genetically identical offspring called clones it is rapid, allowing for quick spread of an organism Produces twice as many offspring Disadvantages: Doesn t allow for variation from one generation to another Based on amount of food available Examples: plant cuttings, Amoeba, bacteria,
Sexual Reproduction Form of reproduction where a new individual is created by fusing two haploid cells (fertilization) Zygote cell created when sperm and egg unite contains two sets of chromosomes Advantage: Allows for genetic variation Offspring look different than parents Disadvantage: slower reproduction rate less reliable more time/energy Ex. Humans, animals
ASEXUAL REPRODUCTION SEXUAL REPRODUCTION What is it? Advantages? Disadvantages?
Differences between meiosis and mitosis? (Picture shows meiosis)
What does meiosis do? 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). This is a good idea if you re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cells produces four haploid cells.
Meiosis is necessary to halve the number of chromosomes going into the sex cells Why halve the chromosomes in gametes? At fertilization the male and female sex cells will provide of the chromosomes each so the offspring has genes from both parents
What else meiosis does 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity. This trick is accomplished through independent assortment and crossing-over. Genetic diversity is important for the evolution of populations and species.
Meiosis converts a diploid cell into a haploid gamete. Before meiosis, cell goes through Interphase, duplicating its chromosomes The result is two genetically identical sister chromatids which remain attached at their centromeres (different than mitosis)
Meiosis I Prophase I : chromatid pairs pair up with their homologous pair, forming a tetrad (two chromosomes on four chromatids)
Meiosis I Prophase I : chromatid pairs pair up with their homologous pair, forming a tetrad. Crossing over - pieces of two homologous chromosomes, switch places and end up on the other chromosome allows for genetic diversity (called genetic recombination)
Meiosis I Metaphase I : Tetrads line up along the center. Independent assortment homologous chromosomes line up randomly Anaphase I : tetrads split and move in opposite directions. Telophase I/Cytokinesis: Two cells form. End product of Meiosis I is two haploid (n) cells.
Meiosis II Prophase II : chromatid pairs move toward the center Metaphase II : The chromatid pairs line up along the center of the cell. Anaphase II : The chromatid pairs split moving the individual chromosomes toward the opposite poles. Telophase II/Cytokinesis : Each of the two cells splits. All are haploid
The haploid cells may develop into gametes. In most male animals, all four cells develop into sperm. In females, one develops into an ootid (egg cell), and three into polar bodies.
Fertilization When the gametes combine (sperm + egg), fertilization occurs. This restores the human chromosome number back to 46. Remember prior to this event each sperm had 23, and the egg had 23. The product is called a zygote. Why is fertilization important? To join to gametes which starts a new life.
