Where Does Meiosis Take Place In Animals

Cells tin reproduce either

asexually via mitosis or
sexually via meiosis

In mitosis , asexual cell division, ane diploid (2n) parent cell gives ascent to two diploid daughter cells that are genetically identical to the original prison cell and to each other.

Where does mitosis occur?
In multicellular organisms, somatic (trunk) cells undergo mitosis to provide new cells for growth or to replace cells that accept been damaged and died.

Some species reproduce via asexually (sometimes called parthenogenesis from the Greek parthen, "virgin" and genesis, "origin". In such species, progenitor cells are produced via mitosis.

A clone is a grouping of genetically identical organisms.

mito

sis

In meiosis , sexual cell division, i diploid (2n) meiocyte (a.chiliad.a. germline prison cell) divides to produce iv haploid (n) daughter cells.
These are further processed to become sex cells (gametes) .

meio

Where does meiosis occur?
In sexually reproducing organisms, a meiocyte (a.k.a. germline cell) undergoes meiosis to produce gametes.

In animals this occurs in the gonads ( ovaries in females; testes in males).
In plants this occurs in the archegonia in females and in the antheridia in males.
In fungi this occurs in specialized structures on fruiting bodies called sporangia .
Protists tin can undergo meiosis to produce haploid versions of themselves which then can fuse with other individuals who accept done the same thing.
Prokaryotes (bacteria and archaea) don't undergo mitosis or meiosis because they are haploid, and don't have linear chromosomes.

Mitosis: Asexual Prison cell Sectionalization

A cell undergoes mitosis to produce two (girl) cells that are genetically identical to the original (parent) cell.

Cellular structures relevant to mitosis or meiosis:

plasma membrane - "gateway" of the jail cell
cytosol - proteinaceous matrix containing the organelles
mitochondria and chloroplasts - energy transduction organelles
- contain circular Deoxyribonucleic acid separate from the nucleus
  - mitochondrial Dna - mtDNA
  - chloroplast DNA - cpDNA
- Dna is circular, not linear
- resembles bacterial Deoxyribonucleic acid
- mtDNA, passed on merely via maternal parent, is sometimes called "Eve's DNA"
nuclear membrane - double membrane surrounding the DNA and forming the nucleus
nucleoplasm - proteinaceous matrix inside the nucleus
nucleolus - dark-staining region inside the nucleus located at the Nucleolar Organizer Region (NOR) of the Deoxyribonucleic acid . It is the site of ribosome associates.
centromere - location of the kinetochore , the physical construction to which spindle fibers attach.

Chromosomes can be classified on the basis of centromere position:

metacentric - at the midpoint of the chromosome
submetacentric - slightly start from the midpoint of the chromosome
acrocentric - close to the finish of the chromosome
telocentric - at the telomere

p arm = short arm of a chromosome

q arm = long arm of a chromosome

By convention, chromosomes are depicted with the short arms pointing upward.

Phases of Mitosis

The phases permit united states of america to divide major events of cell partitioning.
They are divided somewhat arbitrarily. But you lot need to know them, anyhow.

When a cell is non actively dividing, it may be in

interphase - normal state of the cell
Gap 1 - proteins needed for cell division are manufactured
Synthesis (S) phase - DNA is replicated
Gap 2 - short period between Deoxyribonucleic acid synthesis completion and get-go of mitosis
Prophase
- euchromatin condenses into heterochromatin
- chromosomes are now visible every bit joined sister chromatids
- nucleolus disappears (no more ribosome synthesis!)
- mitotic spindle forms
Metaphase
- spindle microtubules have fastened to the kinetochores of the sister chromatids
- duplicated chromosomes line up at the metaphase plate
Anaphase
- spindle pull the sister chromatids apart, cartoon them to contrary poles of the cell.
Telophase
- chromosome sets assemble at reverse poles of the cell
- nuclear envelope forms around each chromosome set
elophase is (commonly) followed past cytokinesis , segmentation of the cytoplasm to course two new cells. Each new daughter cells is genetically identical to the parent cell.

Meiosis: Sexual Cell Sectionalisation

A cell undergoes meiosis to produce iv (girl) cells ( gametes ) that are genetically different from the original (parent) cell ( germline cell ).

Meiosis produces haploid cells from a diploid jail cell in preparation for sexual reproduction.

Why Sex?

The word comes from the Latin secare, which means to cut or carve up something that was once whole.
During meiosis, the making of sexual practice cells, the genetic complement of a parent cell is divided into ii equivalent halves.

Meiosis I is reduction division - the cell goes from having ii homologous chromosomes per pair to having just ane member of each homologous pair.
Meiosis Ii is equational division - the cell divides again, in essentially the same mode as mitosis: the sister chromatids segregate to two new daughter cells.

Stages of Mitosis: Meiosis I

Prophase I

leptonema

lepto

2. spindle fibers brainstorm to form

iii. in animals, centrioles begin migration to contrary poles.

4. chromosomes begin to supercoil

5. "loose" or "rough" pairing of homologs (synapsis is merely starting)

zygonema

zygo

bivalent

2. synapsis is continuing to develop

C. pachynema (adjective = pachytene) from the Greek pachy, pregnant "thick"

2. sister chromatids brainstorm to unwind, becoming visible as two chromosomes joined at the centromere

3. at this point, the bivalent is known as a tetrad

iv. crossing over takes place

(Annotation: homologous pairs are coordinating to a "husband and wife", and the sister chromatids are analogous to identical twins--at least before crossing over.)

D. diplonema (adj = diplotene) from the Greek diplo, meaning "double"

2. chiasmata (crossover points) get visible, sometimes as a complex mesh, since there may be multiple crossover points.

3. annotation that sister chromatids are no longer identical, equally they have undergone crossing over.

(Note: some animals finish here, including humans. Meiosis does not proceed until fertilization or ovulation.)

East. diakinesis from the Greek dia, meaning "beyond" and kinesis, meaning "movement."

terminalization

two. spindle fibers attach to kinetochores.

Metaphase I - spindle fibers suit homologs forth the metaphase plate at the cell's equator.

Anaphase I - spindle fibers separate homologs, conveying them to opposite poles, just sister chromatids are still connected at the centromere. At this point, each two-part member of the former tetrad is known as a dyad

Telophase I , if it occurs (some species skip this step), is a backwards progression to interphase-similar conditions. In Meiosis, it is known as interkinesis .

Meiosis II : the equational division is physically the aforementioned as mitosis, though the genetic composition in the nuclei are different because of crossing over and recombination.

After meiosis, gametogenesis occurs to brand the new haploid cells into gametes.

The generalized animal scenario:

Male :

Testes comprise 2n spermatogonial cells, which constantly renew themselves via mitosis. At some point, some will mature and enter into meiosis to become...
principal spermatocytes [2n --> 2(n + n)]. These diploid cells undergo meosis I to become two...
secondary spermatocytes (northward + n).
Haploid spermatocytes undergo meiosis II to become four spermatids (n).
Further spermatogenesis results in the typical flagellated spermatozoa .

Female :

Ovaries contain 2n oogonial cells, which usually do not renew themselves. At some point in their cellular lifespan, these enter into meiosis I to become
primary oocytes [2n --> 2(n + n)], which undergo meosis I.
- One primary oocyte will become a polar trunk
- The polar body volition divide again to give rise to a second polar body.
- Meanwhile, the other primary oocyte will become a...
- secondary oocyte (n + north), which will undergo meiosis 2 to become one ootid and some other polar body (n).
  4. Farther oogenesis results in the typical cytoplasm-rich ovum .

Plant gametogenesis adds an extra generation. Oversimplifying a bit, we accept...

Male :

Inside the microsporangium of a sporophyte institute, microsporocyte (2n) undergoes meiosis I and 2 to produce haploid microspores (northward).
Each microspore grows into a haploid male person gametophyte (n)
The gametophyte produces sperm (northward) via mitosis.

Female :

Inside the megasporangium of a sporophyte plant, a megasporocyte (2n) undergoes meiosis I and Ii to produce a single haploid megaspore (north)
the three polar bodies produced degenerate, equally in animals
The megaspore grows into the female gametophyte (n), which produces ova (n) via mitosis.

polyspermy: fusion of more than ane sperm with a single egg.

polyploidy

In plants, notwithstanding, polyspermy is i way that polyploidy tin can result in speciation.

Chromosomes: Pairs and Sets

euploidy - the normal number of

chromosome sets
members of all homologous pairs

...expected in a given jail cell (of its species).
(from the Greek eu, meaning "true")

aneuploidy - more or fewer than the normal number of chromosomes per homologous pair (from the Greek an - "abroad" )

nullisomy - a homolgous pair is entirely missing
monosomy - only one fellow member of a homologous pair is present
trisomy - three copies of a homologous chromosome are present
tetrasomy - four copies of a homologous chromosome are present
etc.

Aneuploidies can result from

nondisjunction - three copies of a homologous chromosome are present
- two homologs drift to the same new gamete, leaving the other one "blank"
lagging chromosome - three copies of a homologous chromosome are present
- one member of a homologous pair is non separated into the newly forming gamete at the aforementioned rate as the remainder, and is left out of the nucleus when the nuclear membrane forms.

Autosomal aneuploidies are far more devastating than sex c'some abnormalities; the latter are often survivable, and some persons with sex c'some abnormalities can lead totally normal lives and produce normal offspring.
ploidy - the number of complete chromosome sets in a cell
- haploid - one complete set of chromosomes (in humans, 1 set comprises 23 chromosomes)
- diploid - two complete sets of chromosomes (in humans, two sets of 23 chromosomes)
- triploid - three complete sets of chromosomes
- tetraploid - 3 complete sets of chromosomes
- etc.
Because most eukaryotic organisms are diploid, the condition of having more than two complete sets of chromosomes is known, generically, as polyploidy