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	<references />		<references />


			{{Glossary}}
			{{Footer}}

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Y chromosome

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	* ''SRY'' encodes a 204 amino acid protein that is a member of the HMG (High mobility group) box class of DNA-binding proteins. Transcription factors bind to specific sites of DNA and regulates the transcription (expression) of other genes.		* ''SRY'' encodes a 204 amino acid protein that is a member of the HMG (High mobility group) box class of DNA-binding proteins. Transcription factors bind to specific sites of DNA and regulates the transcription (expression) of other genes.
	\|}		\|}

			==References==

			<references />

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			==Molecular Changes==
			There are several important changes that occur in this new diploid cell beginning the very first mitotic cell divisions and expressing a new genome.

			The oocyte arrested in meiosis is initially quiescent in terms of gene expression, and many other animal models of development have shown maternal RNAs and proteins to be important for early functions.

			The new zygote gene expression is about cycles of mitosis and maintaining the toptipotency of the stem cell offspring cells.

			The morula gene expression supports the formation of two populations of cells the trophoblast (trophectoderm) and embryoblast (inner cell mass), each having different roles in development, while maintaining the toptipotency of these populations.

			Current research is now also pointing to non-genetic mechanisms or epigenetics as an additional mechanism in play in these processes.

			:'''Links:''' [[Cell Division - Mitosis]] \| [[Molecular Development - Epigenetics]]

			===Genome Expression===
			The following figure is from a recent study<ref name="PMID20890283"><pubmed>20890283</pubmed>\| [http://www.nature.com/nbt/journal/vaop/ncurrent/full/nbt.1686.html Nat Biotechnol.]</ref> using video and genetic analysis of ''in vitro'' human development during week 1 following fertilization.

			[[File:Model human blastocyst development.jpg\|600px]]

			* EGA - embryonic genome activation
			* ESSP - embryonic stage–specific pattern, four unique embryonic stage–specific patterns (1-4)

			:'''Links:''' [[:File:Model human blastocyst development.jpg\|Figure with legend]] \| [[Quicktime_Movie_-_Blastocyst_Development\|Blastocyst Quicktime Movie]] \| [[Movie_-_Blastocyst_Development\|Blastocyst Flash Movie]]

			===Telomere Length===
			A recent paper has measured telomere length in human oocyte (GV, germinal vesicle), morula and blastocyst and found changes in this length in preimplantation embryos.<ref name="PMID20573647"><pubmed>20573647</pubmed>\| [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2930518 PMC2930518] \| [http://molehr.oxfordjournals.org/content/16/9/685.long Mol Hum Reprod.]</ref> Telomeres are the regions found at the ends of each chromosome and involved in cellular ageing and the capacity for division. The regions consist of repeated sequences protecting the ends of chromosomes and harbour DNA repair proteins. In the absence of the enzyme telomerase, these regions shorten during each cell division and becoming critically short, cell senescence occurs.
			{\|
			\| [[File:Early_human_telomeres.jpg\|400px]]
			\| [[File:Early_human_telomere_length.jpg\|400px]]
			\|-
			\| Early human telomeres<ref name="PMID20573647" />
			\| Early human telomere length<ref name="PMID20573647" />
			\|}


			== Sex Determination ==
			--[[User:S8600021\|Mark Hill]] 13:21, 9 May 2011 (EST) These concepts will be covered later in detail with BGDB - Sexual Differentiation.

			Mammalian sex determination is regulated by chromosomes.
			* Females have two X chromosomes. ('''XX''')
			* Males have a single X and a small Y. ('''XY''')
			* The X and Y chromosome are morphologically and functionally different from each other.
			* Evolutionary studies have shown that the Y was once the homologous pair for X.
			* It is only in the last 5 years that we have some idea about how these two types of chromosomes may be regulated and genes of importance located upon them.

			===X chromosome===
			{\|
			\| [[File:Human idiogram-chromosome X.jpg\|Human idiogram-chromosome X.jpg]]
			\|
			'''In females''' - the main scientific problem was understanding gene dosage, only one copy of X chromosome is needed to be genetically active the other copy is inactivated (More? [[Molecular_Development_-_X_Inactivation\|X Inactivation]].

			About the X Chromosome
			* 155 million base pairs
			* In contrast to the Y chromosome, the X chromosome contains about 5% of the haploid genome and encodes house-keeping and specialized functions.
			* Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development
			* An early discovery (1961) was that in order to have correct levels of X chromosome gene/protein expression (gene dosage), females must "inactivate" a single copy of the X chromosome in each and every cell. The initiator of the X inactivation process was discovered (1991) to be regulated by a region on the inactivating X chromosome encoding an '''X''' '''i'''nactive '''s'''pecific '''t'''ranscript (XIST), that acts as RNA and does not encode a protein.
			* The genetic content of the X chromosome has been strongly conserved between species because these genes have become adapted to working as a single dose - Ohno's law
			* X inactivation occurs randomly throughout the embryo, generating a mosaic of maternal and paternally derived X chromosome activity in all tissues and organs. This can be seen in the fur colour of tortoiseshell cats.
			\|}

			===Y chromosome ===
			{\|
			\| [[File:Human_idiogram-chromosome_Y.jpg]]
			\|
			'''In males''' - the main scientific problem was understanding what on the Y chromosome determined "maleness", and how this is done.

			About the Y Chromosome
			* 59 million base pairs, hypervariable in length, mostly non-functional repeats
			* Current known protein-coding genes = 48 including ''SRY''
			* ''SRY'' encodes a 204 amino acid protein that is a member of the HMG (High mobility group) box class of DNA-binding proteins. Transcription factors bind to specific sites of DNA and regulates the transcription (expression) of other genes.
			\|}

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2011-08-02T22:37:49Z

Created page with "{{Template:2011Lab2}}"

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2011 Lab 2 - Week 1 - Revision history

S8600021 at 00:53, 4 August 2011

S8600021: /* Y chromosome */

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S8600021: Created page with "{{Template:2011Lab2}}"