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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

where is the pectoral gridle located?
Tiania Reply
What is hypotonic
Bright Reply
what is hypotonic
Dangaya
the difference between the two cells
Obeng Reply
explain the courses and the correction of lon term sightedness and short term sightedness
Isaac Reply
why drinking excess alcohol causes thirst and dehydration
uwikuzo Reply
Can we chat about nutrition please?
Elia
yes
Uzair
sure
Uzair
Uhm why is it so important to follow the nutritional process?
Elia
what is reproduction
smart Reply
it is d act of bringing young ones to life
Oyebanji
to ensure survival of a species🚴‍♀️
Michelle
what is a genotype
Collins
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smart
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smart
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
Pallavi
what is size of cell
Mohd Reply
what is size of Hart
Mohd
nanometers=um sign thingie
Michelle
microns=nanometers
Michelle
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
Michelle
give me the elements of the soil
Iguma Reply
Air, water, organic matter, inorganic matter
Tshwano
soil water humus air
Veronicah
yap
Beloved
silica, iron
Patience
potassium, sulfur, calcium, carbon
Michelle
what is cell
iyaji Reply
A cell is a smallest fundamental unit of a living organisms.
Kem
the basic structural and functional unit of life
Patience
what is size of cell
Mohd
all things are made up of.....all things cannot exist without pre-exisiting cells...check out the 16th ce tury to learn more about microscope use and cells. i will give a hint: Mr. L.
Michelle
we are all made of cells
Michelle
Nutrition - sensitive intervention
Therowda Reply
what does the sori In fern mean
arhin Reply
biology is the study .exactly what is life?
Jerry
i'm sorry , the study of life
Jerry
How is food distributed to all parts of cytoplasm
Therowda
how can U identify a person through his blood
Frankyx Reply
through genetic fingerprinting where specific DNA sequences in a person genome can be identified.
Pallavi
by help of genetics and DNA test
Meerbadini
can it also be detected using an RNA test
Frankyx
environmental biology
Ojesola Reply
what is phytoplankton
Ojesola
What is anabolism
Treasure Reply
the break down of substance
Aunty

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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