Difference between revisions of "Meiosis"
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(A cell becomes haploid in meiosis I. Check your textbooks.) |
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| − | + | '''Meiosis''' is the process by which a [[diploid cell|diploid (2n) cell]] forms four [[gamete]]s. Meiosis differs from [[mitosis]] as meiosis I involves chromosomal content being recombinantly halved.<ref>Wile, Jay L. ''Exploring Creation With Biology''. Apologia Educational Ministries, Inc. 1998.</ref> | |
| − | Educational Ministries, Inc. 1998</ref> | ||
==Overview of Meiosis== | ==Overview of Meiosis== | ||
| + | [[Image:Meiosis.gif|thumb|150px|left|Meiosis Overview]] | ||
Meiosis is involved in producing genetic [[variation]] within a species and is part of the process of [[sexual reproduction]]. Two stages occur in meiosis, each split down into several fundamental processes. Meiosis I is a reduction division<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref> resulting in two [[haploid]] daughter nuclei from one [[diploid]] cell. Meiosis II is very similar to mitosis, where the genetic material in each of the two meiosis I daughter nucleus is halved to form four gametes. | Meiosis is involved in producing genetic [[variation]] within a species and is part of the process of [[sexual reproduction]]. Two stages occur in meiosis, each split down into several fundamental processes. Meiosis I is a reduction division<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref> resulting in two [[haploid]] daughter nuclei from one [[diploid]] cell. Meiosis II is very similar to mitosis, where the genetic material in each of the two meiosis I daughter nucleus is halved to form four gametes. | ||
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There are six stages to meiosis I: | There are six stages to meiosis I: | ||
#Early prophase I. This is identical to mitosis early prophase where: | #Early prophase I. This is identical to mitosis early prophase where: | ||
| − | ##[[chromosome | + | ##[[chromosome]]s become visible due to condensation of [[chromatin]] |
#Middle prophase I. | #Middle prophase I. | ||
##[[homologous]] chromosomes pair up in synapsis to form bivalents | ##[[homologous]] chromosomes pair up in synapsis to form bivalents | ||
##[[centrioles]] move to opposite poles of the cell | ##[[centrioles]] move to opposite poles of the cell | ||
#Late prophase I. | #Late prophase I. | ||
| − | ##nuclear envelope | + | ##nuclear envelope dissolves |
##[[nucleolus]] completely disappears | ##[[nucleolus]] completely disappears | ||
##crossing over of chromatids within bivalents may occur to form a [[chiasma]] (pl. chiasmata) | ##crossing over of chromatids within bivalents may occur to form a [[chiasma]] (pl. chiasmata) | ||
| Line 46: | Line 46: | ||
#Anaphase II | #Anaphase II | ||
##centromeres divide | ##centromeres divide | ||
| − | ##individual chromatids are moved | + | ##individual chromatids are moved the poles of the cell by microtubules, centromeres first |
#Telophase II | #Telophase II | ||
##spindle dissolves | ##spindle dissolves | ||
| Line 60: | Line 60: | ||
<references/> | <references/> | ||
| − | [[Category:Biology]] | + | [[Category:Cellular Biology]] |
| − | [[Category:Genetics]] | + | [[Category:Molecular Genetics]] |
Latest revision as of 01:50, August 10, 2020
Meiosis is the process by which a diploid (2n) cell forms four gametes. Meiosis differs from mitosis as meiosis I involves chromosomal content being recombinantly halved.[1]
Overview of Meiosis
Meiosis is involved in producing genetic variation within a species and is part of the process of sexual reproduction. Two stages occur in meiosis, each split down into several fundamental processes. Meiosis I is a reduction division[2] resulting in two haploid daughter nuclei from one diploid cell. Meiosis II is very similar to mitosis, where the genetic material in each of the two meiosis I daughter nucleus is halved to form four gametes.
The stages involved in mitosis, meiosis I and meiosis II are:
- Prophase
- Metaphase
- Anaphase
- Telophase
The names of these stages can be memorised by the phrase PMAT.
Meiosis I
There are six stages to meiosis I:
- Early prophase I. This is identical to mitosis early prophase where:
- chromosomes become visible due to condensation of chromatin
- Middle prophase I.
- homologous chromosomes pair up in synapsis to form bivalents
- centrioles move to opposite poles of the cell
- Late prophase I.
- Metaphase I.
- bivalents line up along equator of spindle, attached to centromeres
- Anaphase I.
- unlike mitosis, centromeres do not divide
- whole chromosomes move to spindle of cell, centromeres first, pulled by microtubules.
- Telophase I
- spindle dissolves
- nuclear envelopes form around the two daughter nuclei
- a nucleolus reforms in each of the two daughter nuclei
- cytokinesis may occur - most animal cells will undergo cytokinesis but many plant cells pass into meiosis II without doing so.
Meiosis II
Meiosis II is very similar to mitosis, with the exception that four haploid cells are formed. The stages listed below occur in both of the meiosis I daughter cells:
- Prophase II.
- nuclear envelope dissolves
- nucleolus disperses as chromosomes become visible due to condensation of chromatin
- centrioles replicate and move to opposite poles of the cell
- Metaphase II.
- spindle formed
- chromosomes line up across the equator of the spindle
- Anaphase II
- centromeres divide
- individual chromatids are moved the poles of the cell by microtubules, centromeres first
- Telophase II
- spindle dissolves
- nuclear envelopes form around the four daughter nuclei
- a nucleolus reforms in each of the four daughter nuclei
- cytokinesis