<< Chapter < Page Chapter >> Page >

Review the process of meiosis, observing how chromosomes align and migrate, at Meiosis: An Interactive Animation .

Meiosis ii

In some species, cells enter a brief interphase, or interkinesis    , before entering meiosis II. Interkinesis lacks an S phase, so chromosomes are not duplicated. The two cells produced in meiosis I go through the events of meiosis II in synchrony. During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes. Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis.

Prophase ii

If the chromosomes decondensed in telophase I, they condense again. If nuclear envelopes were formed, they fragment into vesicles. The centrosomes that were duplicated during interkinesis move away from each other toward opposite poles, and new spindles are formed.

Prometaphase ii

The nuclear envelopes are completely broken down, and the spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.

Metaphase ii

The sister chromatids are maximally condensed and aligned at the equator of the cell.

Anaphase ii

The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell.

This illustration compares chromosome alignment in meiosis I and meiosis II. In prometaphase I, homologous pairs of chromosomes are held together by chiasmata. In anaphase I, the homologous pair separates and the connections at the chiasmata are broken, but the sister chromatids remain attached at the centromere. In prometaphase II, the sister chromatids are held together at the centromere. In anaphase II, the centromere connections are broken and the sister chromatids separate.
The process of chromosome alignment differs between meiosis I and meiosis II. In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I. In anaphase I, the homologous chromosomes are separated. In prometaphase II, microtubules attach to the kinetochores of sister chromatids, and the sister chromatids are arranged at the midpoint of the cells in metaphase II. In anaphase II, the sister chromatids are separated.

Telophase ii and cytokinesis

The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover. The entire process of meiosis is outlined in [link] .

This illustration outlines the stages of meiosis. In interphase, before meiosis begins, the chromosomes are duplicated. Meiosis I then proceeds through several stages. In prophase I, the chromosomes begin to condense and the nuclear envelope fragments. Homologous pairs of chromosomes line up, and chiasmata form between them. Crossing over occurs at the chiasmata. Spindle fibers emerge from the centrosomes. In prometaphase I, homologous chromosomes attach to the spindle microtubules. In metaphase I, homologous chromosomes line up at the metaphase plate. In anaphase I, the spindle microtubules pull the homologous pairs of chromosomes apart. In telophase I and cytokinesis, the sister chromatids arrive at the poles of the cell and begin to decondense. The nuclear envelope begins to form again, and cell division occurs. Meiosis II then proceeds through several stages. In prophase II, the sister chromatids condense and the nuclear envelope fragments. A new spindle begins to form. In prometaphase II, the sister chromatids become attached to the kinetochore. In metaphase II, the sister chromatids line up at the metaphase plate. In anaphase II, the sister chromatids are pulled apart by the shortening spindles. In telophase II and cytokinesis, the nuclear envelope forms again and cell division occurs, resulting in four haploid daughter cells.
An animal cell with a diploid number of four (2 n = 4) proceeds through the stages of meiosis to form four haploid daughter cells.

Comparing meiosis and mitosis

Mitosis and meiosis are both forms of division of the nucleus in eukaryotic cells. They share some similarities, but also exhibit distinct differences that lead to very different outcomes ( [link] ). Mitosis is a single nuclear division that results in two nuclei that are usually partitioned into two new cells. The nuclei resulting from a mitotic division are genetically identical to the original nucleus. They have the same number of sets of chromosomes, one set in the case of haploid cells and two sets in the case of diploid cells. In most plants and all animal species, it is typically diploid cells that undergo mitosis to form new diploid cells. In contrast, meiosis consists of two nuclear divisions resulting in four nuclei that are usually partitioned into four new cells. The nuclei resulting from meiosis are not genetically identical and they contain one chromosome set only. This is half the number of chromosome sets in the original cell, which is diploid.

Questions & Answers

what is genetic engineering
Mavis Reply
what are the three main type of ecosystem
Mavis
biosphere,
Bigenis
what is mitochondria
Might Reply
please what's genetics erngee
Abanke Reply
what is genetic engineering
Eveline Reply
what is the meaning of term mitosis
Lwitiko Reply
outline the significance of mitosis to organisms
Lwitiko
significant of meiosis are to increase in variation and leads to the formation of haploid gamete
Eveline
thanks
Abanke
name the resources to be conserved
Oreva Reply
define natural resources
Oreva
name the agencies responsible for the conservation of natural resources
Oreva
land,water,forests,
Kiiza
nema,uwa
Kiiza
wassup guyz
Peace
land ,water
Erika
Good Land and Water
garnhial
food, fish, livelihoods,forest, land and water
garnhial
explain the importance of carbon dioxide in the body
Kiiza Reply
how does that works
SAMUEL
diagram of Prokaryotic cells
Magreth Reply
where is it?
Yazi
ʜɪ
Malikie
ʜɪ
Malikie
where is the diagram?
Yazi
waiting.....
Yazi
what
Malikie
good morning guyz
Joelia
gd morning
Hannalyn
morning how are u doing
Paul
doing all fyn en u
Joelia
👍👍👍
Gruxz
morning everyone.. by is Grace we have be saved... Ephesians 2:8....
Cosmo
hi
Kisa
hey guys am new
Ellie
u a most wlcm
Joelia
🍑🐕
Ken
Hello guys im new
Sulaiman
u are welcome
Peace
thanks
Ellie
..amitabatha..
Ken
He guys happy New month
Peace
hello everyone,I'm new here!!
Reine
welcome
James
thanks so much!!
Reine
how re u Reine Balla
James
Happy New mnth to guys
Peace
HAPPY new month to u
James
Thanks and same to u
Peace
welcome one more peace
James
hi guys
Tafadzwa
Define the term Biology element atom
James
my name is rons am asking the question what is blood compatibility
Rons
Do you really no the one you text with.
Israel
I'm fine James, just boredom want to finish me!!
Reine
what is a cell of a bacteria called
Sahfe Reply
what is genotype
James
genotype: this is the combination of alleles an organism has for a given characteristic..
Cosmo
what is maiotic
Gabriel Reply
what is sexual reproduction
Gabriel
what are the effects of concentration gradient in the uptake of water by plant's
Harleen Reply
ls it ok if you have sex during pregnancy
Kags Reply
no
Bernard
yes!!!
Yazi
Yes
Babie
hello
Cabdi
Babie Maseuse .. Hello .. how are you ?
kf
yes it make the baby's strength stay longer
REAL
Who are you?
Babie
why not it's nicer and more enjoyable more than ok for the woman
Lamin
danso from the Gambia and you why do you ask
Lamin
as long as the woman is comfortable and in any possible position good for her
Lamin
unless medically advised to stop or hault and those conditions are also applicable to certain problem in pregancies. Pls any further comment pls never hesitate to ask
Lamin
how tell us
Tony
an assignment for you pls
Lamin
it's recommended
Nyakato
Hello
george
hi how are you?
Lamin
Fine
george
hello everyone
Cosmo
Good night to everyone am from Zambia may the Grace of the Lord be with you all
Cosmo
u too hv gd dreams
Joelia
thanks colleagues and wish you all the best insha Allah
Lamin
InshaAllah
Joelia
Marsha Allah
Lamin
yes
James
What is the meaning of organ
Ronald Reply
tissue combined to form organ
zameer
join
Elishs
orga- these are tissues join together to perform a specific functions.
Elishs
then what are tissues
Kags
group of cells working together to perform a particular function
Harleen
tissue are group of cells put together to perform a certain goal
Bernard
What will happen when read blood cell placed in 0.5 % Nacl solution
zameer Reply
what is biology
Tariro Reply
biology is the study of living organisms
Bernard
examply is the study of.
Nantamu
biology is the study of life.
Nantamu
biology is the study of living things
Lwitiko

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask