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The first week of human development begins with fertilization of the egg (oocyte) by sperm forming the zygote. Both the oocyte and sperm have to have half the DNA (haploid) to forn the zygote (diploid). This is achieved by a special form of cell division that only occurs in species that undergo sexual reproduction, meiosis. Meiosis differs from mitosis in that the cells produced have recombuned their DNA and only contain half the normal cell's DNA content and recomThese notes also cover events before fertilization formation of both the egg and sperm, gametogenesis. Cell division can occur in 2 forms, mitosis and meiosis. Mitosis can occur in all cells, while meiosis only occurs during the formation of the sex gametes. |
Initially, there is a halving of choromosomal content in the gametes, which is restored by fertilization, allowing genetic recombination to occur. This is then followed by a series of cell divisions without cytoplasmic growth.
I have also included in the Week 1 notes
information about male sex determination and X
inactivation, which are not really specific to the
first week of development.
Page Links: Introduction | Some Recent Findings | Meiosis Overview | Differences in Mammalian Meioses | Polar Bodies | Comparison of Meiosis/Mitosis | Abnormalities | References | Glossary
Related Pages: Cell division | Mitosis | Gamete Formation | Oogenesis | Spermatogenesis |
Akiyama T, Nagata M, Aoki F. Inadequate histone deacetylation during oocyte meiosis causes aneuploidy and embryo death in mice. Proc Natl Acad Sci U S A. 2006 May 9;103(19):7339-44.
"It was recently reported that histones are globally deacetylated in mammalian oocytes during meiosis but not mitosis. ... The high incidence of aneuploidy in the embryos of older females may be due to inadequate meiotic histone deacetylation."
Wang Q, Yin S, Ai JS, Liang CG, Hou Y, Chen DY, Schatten H, Sun QY. Histone deacetylation is required for orderly meiosis. Cell Cycle. 2006 Apr;5(7):766-74.
"The results showed that subcellular translocation, expression level and phosphorylated modification of histone deacetylase 1 were temporally regulated and likely to coparticipate in the establishment of histone acetylation profiles in oocyte meiosis."
There are several full versions of this content as a lecture available online from UNSW Cell Biology website Medicine- Society and Health , Science- Cell Biology
In female gametogenesis only a single (1) haploid egg is produced from meiosis. In male gametogenesis four (4) haploid sperm are produced from meiosis.
So what happens to all the extra DNA in producing this single egg?
In Meiosis 1 the "extra" DNA is excluded to the periphery as a 1st polar body, which encloses the extra DNA.
In Meiosis 2 the "extra" DNA is once again excluded as a 2nd polar body. The first polar body may also under go meiosis 2 producing a 3rd polar body.
These polar bodies are not gametes. These polar bodies appear to have no other function than to dispose of the extra DNA.
After DNA replication 2 nuclear (and cell) divisions required to produce haploid gametes Each diploid cell in meiosis produces 4 haploid cells Each diploid cell mitosis produces 2 diploid cells only one pair of homologous chromosomes is shown
Meiotic Nondisjunction
Occurs when homologues fail to separate during meiotic division I or II
Down Syndrome Caused by an extra copy of chromosome 21.
Genome Modifications
chromosomal translocations
Philadelphia chromosome
Chronic myelogenous leukemia
Piece of Chr9 exchanged with Chr22
Generates truncated abl
Overstimulates cell production
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Old Glossary |
Links: Journals | Online Textbooks | Search Textbooks | Reviews | Articles | 1999 Refs | Search PubMed | Glossary
Molecular Biology of the Cell Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002 Meiosis
Developmental Biology Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000Meiosis
Molecular Cell Biology Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999 Meiosis Figure
Search NLM Online Textbooks meiosis Molecular Biology of the Cell | The Cell- A molecular Approach
Reviews
Burgoyne PS, Mahadevaiah SK, Turner JM. The consequences of asynapsis for mammalian meiosis. Nat Rev Genet. 2009 Mar;10(3):207-16. Review. PMID: 19188923
Location, location, location! Monotremes provide unique insights into the evolution of sex chromosome silencing in mammals. Daish T, Grützner F. DNA Cell Biol. 2009 Feb;28(2):91-100. Review. PMID: 19196046
Maternal origin of the human aneuploidies. Are homolog synapsis and recombination to blame? Notes (learned) from the underbelly. Garcia-Cruz R, Roig I, Caldés MG. Genome Dyn. 2009;5:128-36. Review. PMID: 18948712
Articles
Nongenomic steroid-triggered oocyte maturation: Of mice and frogs. Deng J, Carbajal L, Evaul K, Rasar M, Jamnongjit M, Hammes SR. Steroids. 2009 Jul;74(7):595-601. Epub 2008 Nov 24. PMID: 19071151
Kit ligand promotes first polar body extrusion of mouse preovulatory oocytes. Ye Y, Kawamura K, Sasaki M, Kawamura N, Groenen P, Gelpke MD, Rauch R, Hsueh AJ, Tanaka T. Reprod Biol Endocrinol. 2009 Apr 3;7(1):26. [Epub ahead of print] PMID: 19341483
Search Mar 2009 "meiosis" 17,749 reference articles of which 1,873 were reviews.
Search PubMed: term = meiosis
Molecular Biology of the Cell- References
These are a list of references retrieved in a 2000 search of PubMed.(More? meiosis)
Introduction | Abnormalities | Gamete formation | Cell division | Fertilization | Zygote | Blastocyst | Male sex determination| X inactivation | References | Text only page | WWW Links |
