MITOSIS AND MITOSIS AND MEIOSISMEIOSIS

Cell ReplicationCell Replication

Eukaryotic cell replication Eukaryotic cell replication Cells duplicateCells duplicate Divide into two daughter cells. Divide into two daughter cells.

MitosisMitosis

exact copy of the original cellexact copy of the original cell Includes an exact replication of DNAIncludes an exact replication of DNA Millions of rounds of mitosis take place during Millions of rounds of mitosis take place during

the development of large multicellular the development of large multicellular organismsorganisms

MeiosisMeiosis

The creation of sex cellsThe creation of sex cells Sperm and Egg CellsSperm and Egg Cells

The Cell CycleThe Cell Cycle

The The cell cyclecell cycle is the recurring sequence of is the recurring sequence of events that includes the duplication of a events that includes the duplication of a cell’s contents and its subsequent division.cell’s contents and its subsequent division.

The cell cycle is divided into three phases:The cell cycle is divided into three phases: InterphaseInterphase MitosisMitosis CytokinesisCytokinesis

InterphaseInterphase

3 parts: G1, S, G23 parts: G1, S, G2

Cell copies its DNACell copies its DNA

Prepares for mitosisPrepares for mitosisgrowing to a size that can support cell division, growing to a size that can support cell division,

replicating its DNA. replicating its DNA.

DNA Replication (S phase)DNA Replication (S phase)SummarySummary

DNA (double helix) replicates so that from DNA (double helix) replicates so that from one helix of DNA emerge two “daughter” one helix of DNA emerge two “daughter” helices.helices.

Daughter helices are exact copies of the Daughter helices are exact copies of the parental helix.parental helix.

DNA creates daughter helices by using the DNA creates daughter helices by using the parental strands of DNA as a template. parental strands of DNA as a template.

DNA ReplicationDNA Replication

Products of ReplicationProducts of Replication

Interphase: every chromosome is replicatedInterphase: every chromosome is replicated In a human cell, all 46 chromosomes are In a human cell, all 46 chromosomes are

replicated, doesn’t double replicated, doesn’t double Instead, each of the two new chromosomes are Instead, each of the two new chromosomes are

joined together at their middle by a region joined together at their middle by a region called a centromere.called a centromere.

The result is an X-shaped structure The result is an X-shaped structure

New ChromosomeNew Chromosome

MitosisMitosis

Three things must happen:Three things must happen: DNA packaged into chromosomes must DNA packaged into chromosomes must

replicate. replicate. Copies of the chromosomes and organelles Copies of the chromosomes and organelles

must migrate to opposite ends of the cell. must migrate to opposite ends of the cell. The cell must physically split into two The cell must physically split into two

separate cells.separate cells.

MitosisMitosis

ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

PMAT!!!PMAT!!!

Microscopic ProphaseMicroscopic Prophase

MetaphaseMetaphase

MetaphaseMetaphase

AnaphaseAnaphase

AnaphaseAnaphase

TelophaseTelophase

TelophaseTelophase

CytokinesisCytokinesis

Although mitosis officially ends with Although mitosis officially ends with telophase, at this point, the cell is not yet telophase, at this point, the cell is not yet actually split into two new cells. actually split into two new cells.

The final cleavage is not exactly its own stage, The final cleavage is not exactly its own stage, but it does have its own name: cytokinesis, but it does have its own name: cytokinesis, literally “cell division.”literally “cell division.”

Cell Cycle Animation Cell Cycle Animation

http://highered.mcgraw-hill.com/sites/http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.htmlanimation__how_the_cell_cycle_works.html

Basis of Inheritance: MeiosisBasis of Inheritance: Meiosis

Mitosis takes a diploid cell and creates a Mitosis takes a diploid cell and creates a nearly exact copy.nearly exact copy.

Mitosis has two main functions: Mitosis has two main functions: (1) the creation of all of the somatic (body) cells in (1) the creation of all of the somatic (body) cells in

humans and other living organismshumans and other living organisms (2) in organisms that undergo (2) in organisms that undergo asexual asexual

reproductionreproduction

Why is meiosis necessary?Why is meiosis necessary?

This diversity of chromosomes is the result of This diversity of chromosomes is the result of sexual reproductionsexual reproduction, which involves the , which involves the contribution of the genetic material from not contribution of the genetic material from not one, but two parents. one, but two parents.

During sexual reproduction the father’s During sexual reproduction the father’s haploid sperm cell and the mother’s haploid haploid sperm cell and the mother’s haploid ovum (egg) cell fuse to form a single-celled ovum (egg) cell fuse to form a single-celled diploid diploid zygotezygote that then divides billions of that then divides billions of times to form a whole individual. times to form a whole individual.

What is meiosis?What is meiosis?

In order for sexual reproduction to take place, In order for sexual reproduction to take place, however, the parents first need to however, the parents first need to havehave haploid haploid sperm or ova, also called sperm or ova, also called sex cellssex cells, , germ cellsgerm cells, , or or gametesgametes..

Meiosis is the name for the special type of cell Meiosis is the name for the special type of cell division that produces gametes. division that produces gametes.

Process of MeiosisProcess of Meiosis Meiosis involves two cellular divisions: meiosis I Meiosis involves two cellular divisions: meiosis I

and meiosis II. and meiosis II. Each stage of meiosis runs through the same five Each stage of meiosis runs through the same five

stages as discussed in mitosis.stages as discussed in mitosis. During the first round of division, two During the first round of division, two

intermediate daughter cells are produced.intermediate daughter cells are produced. By the end of the second round of meiotic By the end of the second round of meiotic

division (meiosis II), the original diploid (2division (meiosis II), the original diploid (2nn) cell ) cell has become four haploid (has become four haploid (nn) daughter cells. ) daughter cells.

Meiosis IMeiosis I

Interphase IInterphase I DNA replicationDNA replication After replication, the cell has a total of 46 After replication, the cell has a total of 46

chromosomes, each made up of two sister chromosomes, each made up of two sister chromatids joined by a centromere. chromatids joined by a centromere.

Meiosis IMeiosis I

PROPHASE IPROPHASE I The major distinction between mitosis and meiosis The major distinction between mitosis and meiosis

occurs during this phase.occurs during this phase.

Meiosis I : Prophase IMeiosis I : Prophase I

In mitotic prophase, the double-stranded In mitotic prophase, the double-stranded chromosomes line up individually along the chromosomes line up individually along the spindle.spindle.

But in meiotic prophase I, chromosomes line up But in meiotic prophase I, chromosomes line up along the spindle in homologous pairs.along the spindle in homologous pairs.

Then, in a process called Then, in a process called synapsissynapsis, the , the homologous pairs actually join together and homologous pairs actually join together and intertwine, forming a intertwine, forming a tetradtetrad (two chromosomes of (two chromosomes of two chromatids each, or four total chromatids). two chromatids each, or four total chromatids).

Meiosis I : Prophase IMeiosis I : Prophase I

Often this intertwining leads the chromatids of Often this intertwining leads the chromatids of homologous chromosomes to actually exchange homologous chromosomes to actually exchange corresponding pieces of DNA, a process called corresponding pieces of DNA, a process called crossing-over crossing-over or genetic reassortment. or genetic reassortment.

Throughout prophase I, sister chromatids behave Throughout prophase I, sister chromatids behave as a unit and are identical except for the region as a unit and are identical except for the region where crossover occurred. where crossover occurred.

Meiosis I : Metaphase IMeiosis I : Metaphase I

The nuclear membrane breaks down, allowing The nuclear membrane breaks down, allowing microtubules access to the chromosomes. microtubules access to the chromosomes.

Still joined at their crossover regions in Still joined at their crossover regions in tetrads, the homologous pairs of tetrads, the homologous pairs of chromosomes, with one maternal and one chromosomes, with one maternal and one paternal chromosome in each pairpaternal chromosome in each pair

The pairs align in random order. The pairs align in random order.

Meiosis I : Anaphase IMeiosis I : Anaphase I

In contrast to mitosis, the centromeres do not In contrast to mitosis, the centromeres do not splitsplit the entire maternal chromosome of a homologous the entire maternal chromosome of a homologous

pair is pulled to one endpair is pulled to one end the paternal chromosome is pulled to the other endthe paternal chromosome is pulled to the other end

Meiosis I : TelophaseMeiosis I : Telophase

The chromosomes arrive at separate poles and The chromosomes arrive at separate poles and decondensedecondense

Nuclear membranes re-form around themNuclear membranes re-form around them The cell physically divides, as in mitotic The cell physically divides, as in mitotic

cytokinesis. cytokinesis.

Product of Meiosis IProduct of Meiosis I

Meiosis I results in two independent cells.Meiosis I results in two independent cells. One cell contains the maternal homologous pair, One cell contains the maternal homologous pair,

with a small segment of the paternal chromosome with a small segment of the paternal chromosome from crossover. from crossover.

The other cell contains the paternal homologous The other cell contains the paternal homologous pair, likewise with a small segment of the maternal pair, likewise with a small segment of the maternal chromosome. chromosome.

Product differences from MitosisProduct differences from Mitosis

The cells produced in meiosis I are different The cells produced in meiosis I are different from those produced in mitosis because both from those produced in mitosis because both haploid members of the meiotic pair derive haploid members of the meiotic pair derive from random assortments of either the from random assortments of either the maternal or paternal chromosomes from each maternal or paternal chromosomes from each homologous pair (with the exception of the homologous pair (with the exception of the small crossover sections). small crossover sections).

Product differences in MeiosisProduct differences in Meiosis

In mitosis, the cellular division separates sister In mitosis, the cellular division separates sister chromatids and results in diploid cells chromatids and results in diploid cells containing one maternal and one paternal copy containing one maternal and one paternal copy in each diploid pairin each diploid pair

Meiosis IIMeiosis II

These cells These cells do notdo not undergo DNA replication undergo DNA replication before entering meiosis II. before entering meiosis II.

The two cells that move from meiosis I into The two cells that move from meiosis I into meiosis II are haploid—each have 23 meiosis II are haploid—each have 23 replicated chromosomes, rather than the 46 replicated chromosomes, rather than the 46 that exist in cells entering both mitosis and that exist in cells entering both mitosis and meiosis I.meiosis I.

Meiosis IIMeiosis II To distinguish the phases, they are called To distinguish the phases, they are called

prophase II, metaphase II, anaphase II, and prophase II, metaphase II, anaphase II, and telophase II. telophase II.

One important difference between the events of One important difference between the events of meiosis I and II is that no further genetic meiosis I and II is that no further genetic reassortment takes place during prophase II. reassortment takes place during prophase II.

As a result, prophase II is much shorter than As a result, prophase II is much shorter than prophase I.prophase I.

In fact, all of the phases of meiosis II proceed In fact, all of the phases of meiosis II proceed rapidly.rapidly.

Meiosis IIMeiosis II

Metaphase II exactly the way it is in mitotic Metaphase II exactly the way it is in mitotic metaphase. metaphase.

In anaphase II, the sister chromatids separate, In anaphase II, the sister chromatids separate, once again in the same fashion as occurs in once again in the same fashion as occurs in mitotic anaphase. mitotic anaphase. The only difference is that since there was no The only difference is that since there was no

second round of DNA replication; only one set of second round of DNA replication; only one set of chromosomes exists. When the two cells split at the chromosomes exists. When the two cells split at the end of meioisis II, the result is four haploid cells.end of meioisis II, the result is four haploid cells.

Meiosis IIMeiosis II

Of the four haploid cells Of the four haploid cells One cell is composed completely of a maternal One cell is composed completely of a maternal

homologue,homologue, One cell is a maternal homologue with a small One cell is a maternal homologue with a small

segment of paternal DNA from crossover in meiosis segment of paternal DNA from crossover in meiosis I,I,

Another is a complete paternal homologueAnother is a complete paternal homologue The final paternal homologue with a small segment The final paternal homologue with a small segment

of maternal DNA from crossover in meiosis Iof maternal DNA from crossover in meiosis I

Meiosis IIMeiosis II

These four haploid cells are the gametes, the These four haploid cells are the gametes, the sperm or egg cells, that fuse together in sexual sperm or egg cells, that fuse together in sexual reproduction to create new individualsreproduction to create new individuals All four sperm cells will later matureAll four sperm cells will later mature Only one egg cell will mature, the other 3 are polar Only one egg cell will mature, the other 3 are polar

bodies and die offbodies and die off

Spermatogenesis and OogenesisSpermatogenesis and Oogenesis

Meiosis can also be called Meiosis can also be called gametogenesisgametogenesis, , literally “creation of gametes.” literally “creation of gametes.”

The specific type of meiosis that forms sperm The specific type of meiosis that forms sperm is called spermatogenesisis called spermatogenesis

The formation of egg cells, or ova, is called The formation of egg cells, or ova, is called oogenesis. oogenesis.

GametogenesisGametogenesis

The most important thing you need to The most important thing you need to remember about both processes is that they remember about both processes is that they occur through meiosis, but there are a few occur through meiosis, but there are a few specific distinctions between them. specific distinctions between them.

SpermatogenesisSpermatogenesis

The male testes have tiny tubules containing The male testes have tiny tubules containing diploid cells called spermatogonium that diploid cells called spermatogonium that mature to become sperm. mature to become sperm.

The basic function of spermatogenesis is to The basic function of spermatogenesis is to turn each one of the diploid spermatogonium turn each one of the diploid spermatogonium into four haploid sperm cells. into four haploid sperm cells.

SpermatogenesisSpermatogenesis

This quadrupling is accomplished through the This quadrupling is accomplished through the meiotic cell division detailed in the last meiotic cell division detailed in the last section. section.

During interphase before meiosis I, the During interphase before meiosis I, the spermatogonium’s 46 single chromosomes are spermatogonium’s 46 single chromosomes are replicated to form 46 pairs of sister chromatidsreplicated to form 46 pairs of sister chromatids

SpermatogenesisSpermatogenesis

In meiosis II, the two daughter cells go In meiosis II, the two daughter cells go through a second division to yield four cells through a second division to yield four cells containing a unique set of 23 single containing a unique set of 23 single chromosomes that ultimately mature into four chromosomes that ultimately mature into four sperm cells. sperm cells.

Starting at puberty, a male will produce Starting at puberty, a male will produce literally millions of sperm every single day for literally millions of sperm every single day for the rest of his life.the rest of his life.

SpermatogenesisSpermatogenesis

OogenesisOogenesis

Oogenesis involves the formation of haploid Oogenesis involves the formation of haploid cells from an original diploid cell, called a cells from an original diploid cell, called a primary oocyte, through meiosis. primary oocyte, through meiosis.

The female ovaries contain the primary The female ovaries contain the primary oocytes. oocytes.

There are two major differences between the There are two major differences between the male and female production of gametes. male and female production of gametes.

OogenesisOogenesis

First of all, oogenesis only leads to the First of all, oogenesis only leads to the production of one final ovum, or egg cell, from production of one final ovum, or egg cell, from each primary oocyte each primary oocyte

Of the four daughter cells that are produced Of the four daughter cells that are produced when the primary oocyte divides meiotically, when the primary oocyte divides meiotically, three come out much smaller than the fourth. three come out much smaller than the fourth.

OogenesisOogenesis

These smaller cells, called polar bodies, These smaller cells, called polar bodies, eventually disintegrate, leaving only the larger eventually disintegrate, leaving only the larger ovum as the final product of oogenesis. ovum as the final product of oogenesis.

The production of one egg cell via oogenesis The production of one egg cell via oogenesis normally occurs only once a month, from normally occurs only once a month, from puberty to menopause.puberty to menopause.

OogenesisOogenesis