cell division iii) meiosis a) introduction. cell division iii) meiosis meiosis a type of cell...
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Cell DivisionIII) MeiosisMeiosis a type of cell division results in the formation of sex cells, or gametes. in humans it occurs in the testis and ovaries. involves two stages of cell division
both have similarities to the phases in mitosis
the chromosome number of the daughter cells is half that of the parent cell (haploid number or n)
A) Introduction
Cell DivisionIII) Meiosis involves two stages of cell division
both have similarities to the phases in mitosis the chromosome number of the daughter cells is half that of the parent cell (haploid
number or n)
each parent provides half the genetic information to their offspring. each of the 23 chromosomes you receive from your father is
matched up with 23 chromosomes from your mother. the paired chromosomes are called homologous
chromosomes. there are 22 pairs of homologous chromosomes the 23rd pair are the sex chromosomes and are only
partially homologous.
A) Introduction
Cell DivisionIII) Meiosis
the paired chromosomes are called homologous chromosomes. there are 23 pairs of homologous chromosoms the 23rd pair are the sex chromosomes and are only partially
homologous.
during fertilization, a haploid (n = 23) sperm cell unites with a haploid (n = 23) egg cell to produce a diploid (2n = 46) zygote. the zygote will begin dividing by mitosis and become a
multicellular organism.
A) Introduction
Cell DivisionIII) Meiosis meiosis
involves two nuclear division. Meiosis I Meiosis II
produces four haploid cells. meiosis I is called reduction division because the diploid (2n)
chromosome number is reduced to the haploid (n) chromosome number
meiosis II is marked by the separation of the two chromatids. DNA synthesis occurs prior to the two nuclear divisions.*
B) Stages
Cell DivisionIII) Meiosis meiosis II is marked by the separation of the two chromatids. DNA synthesis occurs prior to the two nuclear divisions.
Meiosis I Stages:
Prophase I Metaphase I Anaphase I Telophase I
Prophase I nuclear membrane begins to dissolve centriole splits, parts move to opposite poles and spindle fibres form.
B) Stages
B) Stages
Cell DivisionIII) Meiosis Prophase I
nuclear membrane begins to dissolve centriole splits, parts move to opposite poles and spindle fibres form. chromosomes come together in homologous pairs.
each chromosome of the pair is a homologue and is composed of a pair of sister chromatids. the whole structure is referred to as a tetrad (because there are four
chromatids)
Cell DivisionIII) Meiosis
each chromosome of the pair is a homologue and is composed of a pair of sister chromatids. the whole structure is referred to as a tetrad (because there is four
chromatids)
each pair of homologous chromosomes align side by side (non-sister chromatid to another) this aligning is called synapsis. as the chromosomes synapse they often intertwine
the intertwined chromatids from different homologous break and exchange segments in a process called crossing over.
B) Stages
Cell DivisionIII) Meiosis
this aligning is called synapsis. as the chromosomes synapse they often intertwine
the intertwined chromatids from different homologous break and exchange segments in a process called crossing over.
B) Stages
Cell DivisionIII) Meiosis
this aligning is called synapsis. as the chromosomes synapse they often intertwine
the intertwined chromatids from different homologous break and exchange segments in a process called crossing over.
DNA information is exchanged during the crossing over event. promotes variation within the species.
B) Stages
Cell DivisionIII) Meiosis Metaphase I
homologous chromosomes attach themselves to the spindle fibres and line up along the equatorial plate
B) Stages
Cell DivisionIII) Meiosis Metaphase I
homologous chromosomes attach themselves to the spindle fibres and line up along the equatorial plate
Anaphase I the homologous chromosomes move toward
opposite poles. this is called segregation
reduction division occurs One member of each homologous pair will
be found in each of the new cells.
B) Stages
Cell DivisionIII) Meiosis
this is called segregation reduction division occurs
One member of each homologous pair will be found in each of the new cells.
Telophase I a membrane begins to form around each nucleus.
the chromosomes in the nuclei are not identical because each of the daughter nuclei contains one member of the homologous chromosome pair. homologous chromosomes are similar but
not identical.
B) Stages
Cell DivisionIII) Meiosis
the chromosomes in the nuclei are not identical because each of the daughter nuclei contains one member of the homologous chromosome pair. homologous chromosomes are similar but not identical
Meiosis II Stages:
Prophase II Metaphase II Anaphase II Telophase II
the stages occur at approximately the same time for each of the haploid daughter cells.
there is no replication of chromosomes prior to meiosis II.
B) Stages
Cell DivisionIII) Meiosis the stages occur at approximately the same time for each of the
haploid daughter cells. there is no replication of chromosomes prior to meiosis II.
Prophase II the nuclear membrane dissolves and spindle
fibres form.
B) Stages
Cell DivisionIII) Meiosis Prophase II
the nuclear membrane dissolves and spindle fibres form.
Metaphase II arrangement of each chromosome,
each with two chromatids, along the equatorial plate. chromatids are held together by the
centromere
B) Stages
Cell DivisionIII) Meiosis Prophase II
the nuclear membrane dissolves and spindle fibres form.
Metaphase II arrangement of each chromosome, each with two
chromatids, along the equatorial plate. chromatids are held together by the
centromere
Anaphase II breaking of the attachment between
the two chromatids. migration of chromatids (now called
chromosomes) to opposite poles.
B) Stages
Cell DivisionIII) Meiosis Prophase II
the nuclear membrane dissolves and spindle fibres form. Metaphase II
arrangement of each chromosome, each with two chromatids, along the equatorial plate. chromatids are held together by the centromere
Anaphase II breaking of the attachment between the two chromatids. migration of chromatids (now called chromosomes) to opposite poles.
Telophase II second nuclear division is completed second division of cytoplasm occurs (cytokenesis) four haploid daughter cells are produced
B) Stages
Cell DivisionIII) Meiosis
MITOSIS MEIOSIS
MEIOSIS I
Prophase I
Chiasma
Homologouschromosomepair
Chromosomereplication
Parent cell
2n = 6
Chromosomereplication
Replicated chromosome
Prophase
Metaphase Metaphase I
Anaphase ITelophase I
Haploidn = 3
Daughtercells of
meiosis I
AnaphaseTelophase
2n 2n
Daughter cellsof mitosis
n n n n
MEIOSIS II
Daughter cells of meiosis II
SUMMARY
Meiosis
Occurs during interphase before meiosis I begins
Two, each including prophase, metaphase, anaphase, andtelophase
Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion
Four, each haploid (n), containing half as many chromosomesas the parent cell; genetically different from the parentcell and from each other
Produces gametes; reduces number of chromosomes by halfand introduces genetic variability amoung the gametes
Mitosis
Occurs during interphase beforemitosis begins
One, including prophase, metaphase,anahase, and telophase
Does not occur
Two, each diploid (2n) and geneticallyidentical to the parent cell
Enables multicellular adult to arise fromzygote; produces cells for growth, repair,and, in some species, asexual reproduction
Property
DNAreplication
Number ofdivisions
Synapsis ofhomologouschromosomes
Number ofdaughter cellsand geneticcomposition
Role in theanimal body
B) Stages
Cell DivisionIII) MeiosisGenetic Recombination the formation of new combinations of genes comes about by
independent assortment crossing over
C) Genetic Recombination
Cell DivisionIII) Meiosis comes about by
independent assortment crossing over
Independent Assortment during metaphase I chromosome arrange in homologous pairs along the
equator of the cell. the chromosome of maternal origin is orientated toward one
pole of the cell while the chromosome of paternal origin is oriented towards the other pole
this orientation is “independent” of other homologous pairs it results in gametes having different combinations of parental
chromosomes.
C) Genetic Recombination
Cell DivisionIII) Meiosis Independent Assortment
during metaphase I chromosome arrange in homologous pairs along the equator of the cell. the chromosome of maternal origin is orientated toward one pole of the cell while the
chromosome of paternal origin is oriented towards the other pole this orientation is “independent” of other homologous pairs it results in gametes having different combinations of parental chromosomes.
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C) Genetic Recombination
Cell DivisionIII) Meiosis Independent Assortment
during metaphase I chromosome arrange in homologous pairs along the equator of the cell. the chromosome of maternal origin is orientated toward one pole of the cell while the
chromosome of paternal origin is oriented towards the other pole this orientation is “independent” of other homologous pairs it results in gametes having different combinations of parental chromosomes.
C) Genetic Recombination
Cell DivisionIII) Meiosis Crossing Over
occurs when chromosomes synapse, or pair up during prophase I.
Non-sister chromatids exchange pieces of chromosome. the section that is crossed over may contain hundreds or even
thousands of genes.
can create individual chromosomes with both maternal and paternal genes.
can occur at several points along the non-sister chromatids.
C) Genetic Recombination
Cell DivisionIII) Meiosis Crossing Over
occurs when chromosomes synapse, or pair up during prophase I. non-sister chromatids exchange pieces of chromosome.
the section that is crossed over may contain hundreds or even thousands of genes. can create individual chromosomes with both maternal and paternal genes. can occur at several points along the non-sister chromatids.
Cell DivisionIII) MeiosisGametogenesis the formation of sex cells during meiosis. both females and males follow the same process of meiosis to
develop gametes but there is differences in the final products. the cytoplasm of the female gamete does not divide equally
after each nuclear division. this results:
in one cell, called the ootid, receiving most of the cytoplasm.
three polar bodies that die and are absorbed by the body
D) Gamete Development
Cell DivisionIII) Meiosis
this results: in one cell, called the ootid, receiving most of the cytoplasm. three polar bodies that die and are absorbed by the body
D) Gamete Development
Spermatogenesis the process starts with a diploid germ cell called a
spermatogonium. starting at puberty mitosis forms two spermatogonium
daughter cells. one cell replenishes the spermatogonia one cell develops into a primary spermatocyte
the primary spermatocyte undergoes meiosis I to form two secondary spermatocytes.
the secondary spermatocytes undergo meiosis II to form four spermatids.
D) Gamete Development
D) Gamete Development
the primary spermatocyte undergoes meiosis I to form two secondary spermatocytes.
the secondary spermatocytes undergo meiosis II to form four spermatids.
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Oogenesis oogenesis starts with the diploid germ cell called an
oogonium. each oogonium undergoes mitosis to form two primary
oocytes. three months after conception two million primary oocytes
can be found in the ovaries arrested in prophase I awaiting puberty.
three months after conception two million primary oocytes can be found in the ovaries arrested in prophase I awaiting puberty.
every month after puberty one primary oocyte undergoes meiosis. unequal division of cytoplasm called asymmetrical
cytokinesis occurs. the cell that receives the most cytoplasm is called the
secondary oocyte, the other cell is called the first polar body. the first polar body may or may not go through a
second division to produce a pair of polar bodies.
D) Gamete Development
the cell that receives the most cytoplasm is called the secondary oocyte, the other cell is called the first polar body. the first polar body may or may not go through a second division to
produce a pair of polar bodies.
when sperm penetrates the secondary oocyte it undergoes meiosis II. cytoplasm divides unequally again. the cell with the most cytoplasm becomes the
mature egg. the cell with the least cytoplasm becomes the
second polar body.
D) Gamete Development
D) Gamete Development
cytoplasm divides unequally again. the cell with the most cytoplasm becomes the mature egg. the cell with the least cytoplasm becomes the second polar body.
cool facts about oogenesis asymmetrical cytokinesis allows for one egg to have a large
amount of nutrients (cytoplasm) for the zygote to use prior to implantation
meiosis I and II is not continuous primary oocytes begin meiosis I before birth but stalls in
prophase I until puberty. secondary oocytes stalls at metaphase II until
fertilization occcurs. if fertilization does not occur meiosis II will not be
completed.
D) Gamete Development