Cell Division III) Meiosis A) Introduction. Cell Division III) Meiosis Meiosis a type of cell...

Cell DivisionIII) Meiosis

A) Introduction

A) Introduction

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


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) MeiosisB) Stages

B) Stages


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)


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


this aligning is called synapsis. as the chromosomes synapse they often intertwine


B) Stages


this aligning is called synapsis. as the chromosomes synapse they often intertwine


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


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


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


B) Stages


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


B) Stages


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


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


B) Stages


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B) Stages


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


B) Stages


Cell DivisionIII) MeiosisC) Genetic

Recombination

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.


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.

http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html


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.


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) 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) MeiosisD) Gamete

Development

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


this results: in one cell, called the ootid, receiving most of the cytoplasm. three polar bodies that die and are absorbed by the body


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.



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.


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.



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.


Cell Division III) Meiosis A) Introduction. Cell Division III) Meiosis Meiosis a type of cell...

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