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Meiosis

Meiosis

Meiosis is a type of cell division that, in humans, occurs only in male testes and female ovary tissue, and, together with fertilization, it is the process that is characteristic of sexual reproduction. Meiosis serves two important purposes: it keeps the number of chromosomes from doubling each generation, and it provides genetic diversity in offspring. In this it differs from mitosis, which is the process of cell division that occurs in all somatic cells.

Overview

All of our somatic cells except the egg and sperm cells contain twenty-three pairs of chromosomes, for a total of forty-six individual chromosomes. This number, twenty-three, is known as the diploid number. If our egg and sperm cells were just like our somatic cells and contained twenty-three pairs of chromosomes, their fusion during fertilization would create a cell with forty-six chromosome pairs, or ninety-two chromosomes total. To prevent that from happening and to ensure a stable number of chromosomes throughout the generations, a special type of cell division is needed to halve the number of chromosomes in egg and sperm cells. This special process is meiosis.

Meiosis creates haploid cells, in which there are twenty-three individual chromosomes, without any pairing. When gametes fuse at conception to produce a zygote, which will turn into a fetus and eventually into an adult human being, the chromosomes containing the mother's and father's genetic material combine to form a single diploid cell. The specialized diploid cells that will eventually undergo meiosis to produce the gametes are called primary oocytes in the female ovary and primary spermatocytes in the male testis. They are set aside from somatic cells early in the course of fetal development.

Even though meiosis is a continuous process in reality, it is convenient to describe it as occurring in two separate rounds of nuclear division. In the first round (meiosis I), the two versions of each chromosome, called homologues or homologous chromosomes, pair up along their entire lengths and thus enable genetic material to be exchanged between them. This exchange process is called crossing over and contributes greatly to the amount of genetic variation that we see between parents and their children. Subsequently, the two homologues are pulled toward opposite ends of their surrounding cell, thus creating a haploid cluster of chromosomes at each pole, at which point division occurs, separating the two clusters. Meiosis I is therefore the actual reduction division. At the end of meiosis I, each chromosome is still composed of two sister strands (chromatids) held together by a particular DNA sequence of about 220 nucleotides, called the centromere. The centromere has a disk-shaped protein molecule (kinetochore) attached to it that is important for the separation of the sister chromatids in the second round of meiosis (meiosis II). Meiosis II is essentially the same division process as mitosis. Through the separation of the two sister chromatids, a total of four daughter cells, each with a haploid set of chromosomes, are created.

Meiosis I

Meiosis must be preceded by the S phase of the cell cycle. This is when DNA replication (the copying of the genetic material) occurs. Thus, each chromosome enters meiosis consisting of two sister chromatids joined at the centromere. The first stage of meiosis is a stage called prophase I. First, the DNA of individual chromosomes coils more and more tightly, a process called DNA condensation. The sister chromatids then attach to specific sites on the nuclear envelope that are designed to bring the members of each homologous pair of chromosomes close together. The sister chromatids line up in a fashion that is precise enough to pair up each gene on the DNA molecule with its corresponding "sister gene" on the homologous chromosome. This four-stranded structure of maternal and paternal homologues is also called a bivalent.

Next in prophase I is the process of crossing over, in which fragments of DNA are exchanged between the homologous sister chromatids that form the paired DNA strands. Crossing over involves the physical breakage of the DNA double helix in one paternal and one maternal chromatid and joining of the respective ends. Under the light microscope, the points of this exchange can often be seen as an X-shaped structure called a chiasma.

The exchange of genetic material means that new combinations of genes are created on two of the four chromatids: Stretches of DNA with maternal gene copies are mixed with stretches of DNA with paternal copies. This creation of new gene combinations is called "recombination" and is very important for evolution, since it increases the amount of genetic material that evolution can act upon. A statistical technique known as linkage analysis uses the frequency of recombination to infer the location of genes, such as those that increase a person's risk for certain diseases.

At the beginning of metaphase I, the nuclear envelope has dissolved, and specialized protein fibers called microtubules have formed a spindle apparatus, as also occurs in the metaphase of mitosis. These microtubules then attach to the kinetochore protein disks on the two centromeres of the homologous pair of chromosomes. However, there is an important difference between mitosis and meiosis in the way this attachment occurs. In mitosis, microtubules attach to both faces of the kinetochore and thus separate sister chromatids when they pull apart. In meiosis, because the chiasma structures still hold the homologous sister chromatids together, only one face of each kinetochore is accessible to the microtubules. Since the microtubules can only attach to one face of the kinetochore, the sister chromatids will be drawn to opposite poles as a pair, without separation of the individual chromatids.

At the end of metaphase I, the pairs of homologues line up on the metaphase plate in the center of the cell, the spindle apparatus is fully developed, and the microtubules of the spindle fibers are attached to one side of each of the two kinetochores. In anaphase I, the microtubules begin to shorten, thus breaking apart the chiasmata and pulling the centromeres with their respective sister chromatids toward the two cell poles. The centromeres do not divide, as they do in mitosis. At the final stage of meiosis I, called telophase I, each cell pole has a cluster of chromosomes that corresponds to a complete haploid set, one member of each homologous chromosome pair.

The Sources of Genetic Diversity

It is completely random whether the maternal or paternal chromosome of each pair ends up at a particular pole. The orientation of each pair of homologous chromosomes on the metaphase plate is random, and a mixture of maternal and paternal chromosomes will be drawn toward the same cell pole by chance. This phenomenon is often called "independent assortment," and it creates new combinations of genes that are located on different chromosomes. Thus, we have two levels of gene reshuffling occurring in meiosis I. The first occurs during recombination in prophase I, which creates new combinations of genes on the same chromosome. In contrast to mitosis, the sister chromatids of a chromosome are not genetically identical because of the crossing-over process. Anaphase I then adds the independent assortment of chromosomes to create new combinations of genes on different chromosomes. A total of 223 (8.4 million) possible combinations of parental chromosomes can be produced by one person, and recombination further increases this to an almost unlimited number of genetically different gametes.

Meiosis II

Once both cell poles have a haploid set of chromosomes clustered around them, these chromosomes divide mitotically (without reshuffling or reducing the number of chromosomes during division) during the second part of meiosis. This time, the spindle fibers bind to both faces of the kinetochore, the centromeres divide, and the sister chromatids move to opposite cell poles. At the end of meiosis II, therefore, the cell has produced four haploid groups of chromosomes. Nuclear envelopes form around each of these four sets of chromosomes, and the cytoplasm is physically divided among the four daughter cells in a process known as cytokinesis .

In males, the four resulting haploid sperm cells all go on to function as gametes (spermatozoa). They are produced continuously from puberty onwards. In females, all primary oocytes enter meiosis I during fetal development but then arrest at the prophase I stage until puberty. During infancy and early childhood, the primary oocytes acquire various functional characteristics of the mature egg cell. After puberty, one oocyte a month completes meiosis, but only one mature egg is produced, rather than the four mature sperm cells in males. The other daughter cells, called polar bodies, contain little cytoplasm and do not function as gametes.

Comparison with Mitosis

In summary, the main differences between meiosis and mitosis are that meiosis occurs only in specialized cells rather than in every tissue; it produces haploid gametes rather than diploid somatic cells; and each daughter cell is genetically different from the others due to recombination and independent assortment of homologues, rather than genetically identical. The pairing of homologous chromosomes and crossing over occur only in meiosis.

Chromosomal Aberrations

Meiosis is a very intricate process that requires, among other things, the precise alignment of homologous chromosome pairs and correct attachment of microtubules. During meiosis, errors in chromosome distribution may occur and lead to chromosomal aberrations in the offspring. One example is Down syndrome, where affected children carry three copies of chromosome 21 (trisomy 21). This may be explained by the failure of paired chromosomes or sister chromatids to separate in either sperm or egg, leading to the presence of two copies of chromosome 21. After fertilization with a normal gamete, the zygote will carry three copies, which leads to several phenotypic abnormalities, including mental retardation.

see also Cell, Eukaryotic; Chromosomal Aberrations; Crossing Over; Down Syndrome; Fertilization; Linkage and Recombination; Mitosis; Replication.

Silke Schmidt

Bibliography

Alberts, Bruce, et al. Molecular Biology of the Cell, 3rd ed. New York: Garland Publishing, 1994.

Curtis, Helena, and Susan Barnes. Invitation to Biology, 5th ed. New York: WorthPublishers, 1994.

Raven, Peter H., and George B. Johnson. Biology, 2nd ed. St. Louis, MO: Times Mirror/Mosby College Publishing, 1989.

Robinson, Richard. Biology. Farmington Hills, MI: Macmillan Reference USA, 2001.

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Meiosis

Meiosis

Meiosis is the two-step series of specialized cell divisions that makes sexual reproduction possible. Meiosis produces haploid cells, which contain just one member of every chromosome pair characteristic of an organism. In all animals, specialized cells in the reproductive organs, called germ cells, undergo meiosis to produce haploid gametes (sperm and egg), which then fuse during sexual reproduction to create new diploid embryos. For example, human gametes are haploid and contain twenty-three different chromosomes. All other cells in the human body are diploid, containing two versions of each chromosome for a total of forty-six. Fusion of gametes to form a new embryo restores the diploid number characteristic of the organism, and it mixes maternal and paternal genes to give new combinations of traits. Meiosis itself also yields great genetic diversity in the resultant gametes through two mechanisms: (1) independent assortment of chromosomes at both of the meiotic divisions; and (2) physical exchange of chromosomal regions through a process called crossing over. Both processes create new chromosomal combinations, resulting in an array of genetically diverse gametes from a single individual.

Plants, fungi, and some protists also perform meiosis. In plants, meiosis creates a multicellular haploid organism, called a gametophyte , which in some groups is independent of the diploid plant. Gametes are produced by mitosis of the gametophyte, which then fuse to form the embryo. This cycle is called alternation of generations.

Chromosome Basics and Meiosis Overview

As noted, diploid cells contain pairs of chromosomes, each member of which carries the same set of genes. One member of each pair is inherited from the mother, and one from the father. The two pair members are called homologous chromosomes , or homologs.

Prior to meiosis, the diploid cell replicates its deoxyribonucleic acid (DNA). During replication, each chromosome duplicates itself to form two identical copies, which remain attached at a region known as the centromere . Each copy is known as a chromatid ; thus, each chromosome is composed of two identical sister chromatids.

During meiosis, homologous chromosomes line up and exchange segments, a process called crossing over. Following this, homologs are separated from each other in the first meiotic division. Next, in the second meiotic division, chromatids are separated from each other, in a process which is mechanically identical to mitosis. The result is four haploid cells. The coordination of the two meiotic chromosomal divisions gives meiosis its distinctive characteristics: a reduction in the number of chromosomes by half, accompanied by mixing of parental chromosomes, and swapping of regions between homologous chromosomes.

Meiosis I

Consider a spermatocyte or oocyte about to embark on meiosis. This diploid cell contains one set of chromosomes contributed by its mother and one set of chromosomes contributed by its father. Following DNA replication, the unique aspects of the first division of meiosis (meiosis I) begin. Because meiosis reduces chromosome content, a mechanism must ensure that every final haploid gamete has both the correct number and the correct set of chromosomes, with one member of each homologous pair. Meiosis I guarantees this by keeping each chromatid pair together and aligning homologous pairs of duplicated sister chromosomes prior to the first chromosomal division. The alignment and subsequent separation of pairs of homologous chromosomes during meiosis I thus sets up the mechanism that ensures that all four haploid gametes will contain the correct complement of chromosomes. Interestingly, the mechanism whereby meiosis aligns homologs also results in reciprocal exchanges of DNA between aligned chromosomes.

Alignment of homologous chromosome pairs begins before meiosis I, when each duplicated set of chromosomes seeks its homologous partner pair within the oocyte or spermatocyte. The underlying DNA sequence homology of the similar maternal and paternal chromosome pairs guides this search and eventual alignment along the entire length of each chromosome. The alignment is further mediated and cemented by a three-dimensional zipperlike structure surrounding each set of paired homologous chromosomes, the synaptonemal complex. In the process of these alignment steps, specific enzymes nick and then rejoin DNA at different places along the paired chromosomes. This process of genetic exchange is called meiotic recombination, or crossing over. Crossing over provides an attachment that holds homologous chromosomes temporarily in place and, at the same time, produces progeny chromosomes consisting of a patchwork of material from each of the originals. Thus, the two central characteristics of meiosis, reduction in chromosome number and genetic rearrangements, are intimately intertwined.

Once all sets of chromosome pairs have established at least one such crossing over, correct assortment of chromosomes at meiosis I is ensured. The synaptonemal complexes dissolve and the newly rearranged chromosomes proceed through the second mechanism that generates genetic diversity at meiosis I: They assort independently of one another to opposite poles of the cell pulled by spindle fibers. Whereas one chromosome pair might divide so that its predominantly maternal chromosome moves to the cell's "north" pole, another pair of chromosomes will move its predominantly paternal chromosome to that same north pole. These chromosomal movements are randomly determined, yielding great genetic diversity of gametes in an organism with multiple chromosomes. In an organism with three homologous pairs, there are four different possible chromosome arrangements at the end of meiosis I. In humans there are more than 4 million possible arrangements.

Thus, overall, the first division of meiosis provides two major mechanisms for new genetic combinations: (1) cutting apart and pasting together various segments of homologous chromosomes to yield unique hybrid chromosomes; and (2) independent assortment of maternal and paternal chromosomes.

Meiosis II and Cytokinesis

As meiosis II begins, each daughter nucleus contains the haploid number of chromosomes (for humans, twenty-three). Each chromosome is composed of two chromatids attached at the centromere. The second division of meiosis separates the chromatids. Once again, spindle fibers provide the pulling power. Once chromatids are separated, they are called chromosomes, and so at the end of meiosis II, each of the four new cells has the haploid number of chromosomes. Following this, cytokinesis occurs, in which the cytoplasm of the original cell is divided and membranes form to separate the new cells. Cytoplasm is divided evenly in sperm, but unevenly in eggs. During egg formation, most of the cytoplasm is allotted to one of the cell products, leaving one functional egg and several "polar bodies" that contain DNA and membrane, but little else. This unequal division gives the single egg a larger store of food to supply the developing embryo after fertilization .

Meiosis versus Mitosis

The alignment of homologous chromosome pairs in meiosis I and the accompanying physical exchanges between aligned chromosomes is unique to meiosis. In mitosis, by contrast, homologous chromosome pairs never or very rarely interact. Each mitotic chromosome duplicates, forming two sister chromatids, and then these two identical sister chromatids separate to opposite poles. While mitosis is specialized to produce entirely identical progeny, meiosis is specialized to produce a wide range of distinctive haploid progeny.

Mistakes in Meiosis

Among the many potential causes of infertility are problems with meiosis. If a person's spermatocytes or oocytes consistently produce sperm or eggs that contain an incorrect number or complement of chromosomes, then there will be great difficulty in producing a viable embryo.

A much more common situation arises from the rare, sporadic occurrence in a normally fertile person of an improper chromosome separation. When two chromosomes fail to separate as they should, a "nondisjunction" event has occurred. Such nondisjunctions are almost always lethal to the egg or sperm, or to the resultant embryo. There are exceptions, however. For example, approximately one out of one hundred men is the result of such a nondisjunction, which gave him an extra X chromosome. Such XXY individuals have Klinefelter's syndrome, a sex chromosome trisomy (three sex chromosomes instead of the normal two) with minor outward manifestations. Down syndrome individuals possess three copies of chromosome twenty-one instead of the normal two; their extra copy resulted from a nondisjunction of those chromosomes during one of the meiotic divisions of one of the parents.

see also Alternation of Generations; Chromosome, Eukaryotic; Cytokinesis; Mitosis; Sex Chromosomes; Sexual Reproduction

Wendy E. Raymond

Bibliography

Griffiths, Anthony J. F., et al. Modern Genetic Analysis. New York: W. H. Freeman and Company, 1999.

"Meiosis and Genetic Recombination." MIT's Biology Hypertextbook. <http://esg-.www.mit.edu:8001/esgbio/mg/meiosis.html>.

"Meiosis Tutorial." The Biology Project. <http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html>.

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meiosis

meiosis (reduction division) A form of nuclear division whereby: (a) each gamete receives only one member of a chromosome pair (this forms one of the bases of Mendel's first law of genetic segregation); and(b) genetic material can be exchanged between homologous chromosomes. Two successive divisions of the nucleus occur (known as division I and division II), with corresponding cell divisions, following a single chromosomal duplication. Thus a single diploid cell gives rise to four haploid cells. This produces gametes (in animals) or sexual spores (in plants and some protozoa) that have one half of the genetic material or chromosome number of the original cell. This halving of the chromosome number (2n to n) compensates for its doubling when the gametes (n + n) unite to form a zygote (2n) during sexual reproduction. The process occurs during gamete formation in animals or during spore formation in plants and protozoa. The first stage of the first division of meiosis is often called prophase I and for convenience it has been divided into the leptotene, zygotene, pachytene, diplotene, and diakinesis stages; these are not distinct and grade into each other. Chromosomes first appear in the first stage (leptotene) of meiosis, as single threads. The two homologous members of each chromosome pair associate side by side with corresponding loci adhering together: this is called pairing. It occurs during the zygotene stage, each resulting pair being called a bivalent. Thus the apparent number of chromosome threads is half what it was before, being the number of bivalents rather than the number of single chromosomes. During the pachytene stage, each bivalent separates into two sister chromatids (except at the region of the centromere), with some localized breakage and crossing-over of genetic material of both maternal and paternal origin. There are now n groups of four chromatids lying parallel to each other and forming a tetrad. During the diplotene stage, one pair of sister chromatids in each of the tetrads begins to separate from the other pair except at the sites where exchanges have taken place. In these regions the overlapping chromatids form a cross-shaped structure called a chiasma and these chiasmata slip towards the ends of the chromatids so that their position no longer coincides with that of the original cross-overs. This process continues until, during diakinesis, all the chiasmata reach the ends of the tetrads and the homologues can separate during anaphase. At diakinesis the chromosomes coil tightly, so shortening and thickening to form a group of compact tetrads which are well spaced out in the nucleus, and the nucleolus disappears. This ends the prophase I stage of meiosis. During the first division (metaphase to telophase), the nuclear envelope disappears, with the tetrads arranged at the equator of the spindle. The chromatids of a tetrad separate in such a way that maternal chromosomal material is kept distinct from paternal material except at regions distal to the points of crossing-over. This first division produces two secondary gametocytes containing dyads (a dyad is half a tetrad) each of which becomes surrounded by a nuclear envelope. After a short interphase, the second division (prophase II) begins, during which the sister chromatids of a single chromosome are separated. The nuclear membrane disappears once more and the dyads arrange themselves upon the metaphase plate, the chromatids of each dyad being equivalent to one another (except for those regions distal to points of crossing-over). The centromere divides and so allows each chromosome to pass to a separate cell and the process is complete. Four cells result from the two divisions of meiosis. Compare MITOSIS.

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meiosis

meiosis (mīŏ´sĬs), process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells (ovum and sperm), are being formed. Because fertilization consists of the fusion of two separate nuclei, one from each of the sex cells, meiosis is necessary to prevent the doubling of the chromosome number in each successive generation. An ordinary body cell is diploid; i.e., it contains two of each type of chromosome. The members of each pair are known as homologous chromosomes. An ovum or sperm is haploid; i.e., it contains only a single chromosome of each type and, therefore, half the number of chromosomes of the diploid cell. When the two haploid cells fuse, the diploid number is restored, and the plant or animal growing from the fertilized egg (zygote) has the usual diploid number of chromosomes in its cells. Just before meiosis each chromosome replicates to form two identical copies in the form of strands called chromatids joined together at a point called the centromere. In the first stage of meiosis, called the reduction division, the members of each pair of homologous chromosomes lie side by side and crossing over occurs. Each member of the pair then moves away from the other toward opposite ends of the dividing cell, and two nuclei, each with the haploid number of double-stringed chromosomes, are formed. Thus at the beginning of the second meiotic sequence, called the equational division, each cell nucleus contains one chromosome from each homologous pair and each chromosome is of two strands that are identical (except where crossing over has occurred). Then the chromosomes separate into their single strands which move toward opposite ends of the dividing nucleus. The result of meiotic division is four cells, each haploid, with one chromosome of each pair.

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meiosis

meiosis(reduction division) A form of nuclear division whereby each gamete receives only one member of a chromosome pair (this forms one of the bases of Mendel's first law of genetic segregation) and genetic material can be exchanged between homologous chromosomes. Two successive divisions of the nucleus occur, with corresponding cell divisions, following a single chromosomal duplication. Thus a single diploid cell gives rise to four haploid cells. This produces gametes (in animals) or sexual spores (in plants and some protozoa) that have one half of the genetic material or chromosome number of the original cell. This halving of the chromosome number (2n to n) compensates for its doubling when the gametes (n + n) unite (2n) during sexual reproduction. Compare mitosis.

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meiosis

meiosis (reduction division) A type of nuclear division that gives rise to four reproductive cells (gametes) each with half the chromosome number of the parent cell. Two consecutive divisions occur (see illustration). In the first, homologous chromosomes become paired and may exchange genetic material (see crossing over) before moving away from each other into separate daughter nuclei. This is the actual reduction division because each of the two nuclei so formed contains only half of the original chromosomes. The daughter nuclei then divide by mitosis and four haploid cells are produced. See also prophase; metaphase; anaphase; telophase.

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meiosis

meiosis In biology, the process of cell division that reduces the chromosome number from diploid (pairs) to haploid (single set). The first division halves the chromosome number in the cells; the second then forms four haploid ‘daughter’ cells, each containing a unique configuration of the parent cells' chromosomes. In most higher organisms, the resulting haploid cells are the gametes, ova and sperm. In this way, meiosis enables the genes from both parents to combine in a single cell without increasing the overall number of chromosomes. See also mitosis andovary

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meiosis

mei·o·sis / mīˈōsəs/ • n. (pl. -ses / -sēz/ ) 1. Biol. a type of cell division that results in two daughter cells each with half the chromosome number of the parent cell, as in the production of gametes.Compare with mitosis. 2. another term for litotes. DERIVATIVES: mei·ot·ic / mīˈätik/ adj. mei·ot·i·cal·ly / -ik(ə)lē/ adv.

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meiosis

meiosis (reduction division) (my-oh-sis) n. a type of cell division that produces four daughter cells, each having half the number of chromosomes of the original cell. It occurs before the formation of sperm and ova and the normal (diploid) number of chromosomes is restored after fertilization. Compare mitosis.
meiotic (my-ot-ik) adj.

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MEIOSIS

MEIOSIS [Stress: ‘my-OH-sis’]. In RHETORIC, a kind of understatement that dismisses or belittles, especially by using terms that make something seem less significant than it really is or ought to be: for example, calling a serious wound a scratch, or a journalist a hack or a scribbler. Compare LITOTES.

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meiosis

meiosis in rhetoric, another term for litotes. Recorded from the mid 16th century, the word comes via modern Latin, from Greek meiōsis, from meioun ‘lessen’, from meiōn ‘less’.

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meiosis

meiosis (rhet.) † diminishing figure of speech XVI; litotes XVII. — Gr. meíōsis, f. meioûn lessen, f. meíôn less (see MINOR).

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"meiosis." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 23 Jul. 2017 <http://www.encyclopedia.com>.

"meiosis." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (July 23, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/meiosis-2

"meiosis." The Concise Oxford Dictionary of English Etymology. . Retrieved July 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/meiosis-2

meiosis

meiosisglacis, Onassis •abscess •anaphylaxis, axis, praxis, taxis •Chalcis • Jancis • synapsis • catharsis •Frances, Francis •thesis • Alexis • amanuensis •prolepsis, sepsis, syllepsis •basis, oasis, stasis •amniocentesis, anamnesis, ascesis, catechesis, exegesis, mimesis, prosthesis, psychokinesis, telekinesis •ellipsis, paralipsis •Lachesis •analysis, catalysis, dialysis, paralysis, psychoanalysis •electrolysis • nemesis •genesis, parthenogenesis, pathogenesis •diaeresis (US dieresis) • metathesis •parenthesis •photosynthesis, synthesis •hypothesis, prothesis •crisis, Isis •proboscis • synopsis •apotheosis, chlorosis, cirrhosis, diagnosis, halitosis, hypnosis, kenosis, meiosis, metempsychosis, misdiagnosis, mononucleosis, myxomatosis, necrosis, neurosis, osmosis, osteoporosis, prognosis, psittacosis, psychosis, sclerosis, symbiosis, thrombosis, toxoplasmosis, trichinosis, tuberculosis •archdiocese, diocese, elephantiasis, psoriasis •anabasis • apodosis •emphasis, underemphasis •anamorphosis, metamorphosis •periphrasis • entasis • protasis •hypostasis, iconostasis

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"meiosis." Oxford Dictionary of Rhymes. . Encyclopedia.com. 23 Jul. 2017 <http://www.encyclopedia.com>.

"meiosis." Oxford Dictionary of Rhymes. . Encyclopedia.com. (July 23, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/meiosis-0

"meiosis." Oxford Dictionary of Rhymes. . Retrieved July 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/meiosis-0