The School of Biomedical Sciences Wiki - User contributions [en]

Coulomb

2012-10-23T10:51:11Z

110097981: Created page with "A current of electricity or charge being transported at 1 amp per seond. It can also be measured as 1 farad * the potential difference of a volt."

A current of electricity or charge being transported at 1 amp per seond.

It can also be measured as 1 farad * the potential difference of a volt.

Meiosis

2011-12-01T16:05:04Z

110097981:

Meiosis is a type of cell division. It can only occur in [[Diploid|diploid]] cells, resulting in four unidentical [[Haploid|haploid]] [[Daughter cells|daughter cells]]. This contrasts to mitosis which can occur in both [[Haploid|haploid]] and [[Diploid|diploid]] cells, producing only two identical daughter cells. There are two stages of Meiosis, Meiosis I and II. This leads to the nucleus diving twice but chromosome replication only occuring once. Like mitosis, chromosomes in meiosis have duplicated in Interphase, during S phase.  

= Meiosis I <ref>Hartl DL and Jones EW (2009) Genetics: Analysis of Genes and Genomes, Seventh Edition, USA, Jones and Bartlett Publishers</ref> =

Meiosis 1 is separated into 4 stages. These are Prophase I, Metaphase I, Anaphase I and Telophase I.

== Prophase I ==

During prophase I chromosomes pair, condense and crossing over occurs between non-sister chromotids. It is separated into 5 different stages. Similar to mitosis, cetrioles move to opposite poles and spindle fibres start to form. 

=== Leptotene ===

Leptotene is the first stage of Prophase I. During the Leptotene stage chromosomes coil and condense. This is whne the chromosomes first become visible.

=== Zygotene ===

During Zygotene the homologous chromosomes pair up and the [[Synaptonemal Complex|synaptonemal complex]] between the homologous chromosomes start forming.

=== Pachytene ===

Synapsis is now complete and the a [[Bivalent|bivalent]] (pair of homologous chromosomes) is formed. Chiasmata (singular: chiasma) form between non-sister chromotids of homolohous chromosomes. This is the point where crossing over occurs and DNA exchange occurs. 

=== Diplotene ===

The snaptonemal complex breaks down, allowing the chromosomes to separate. The chiasmata are now visible and are point at which the chromosomes are still held together. 

=== Diakensis ===

During diakenesis the nuclear envelope starts to breakdown. The bivalents are now ready for metaphase 

== Metaphase I ==

Bivalents or tetrads (four chromotids) align on on the metaphase plate (the equator of the cell) and spindle fibres attach to the kinetichores, protein structures located at the centromeres. 

== Anaphase I ==

Disjunction occurs. This is when the mitotic spindles pull the tetrads apart to forming dyads, which migrate to opposite poles. 

== Telophase I ==

Nuclear envelope may form around the dyads and cytokinesis (cell division) occurs. 

== Interphase ==

Interphase does not have to occur between Telophase I and Prophase II, but it can occur. Unlike traditional interphase, there is no DNA replication but growth and biosynthetic activities can still occur. 

= Meiosis II   =

= Prophase II =

Unlike Prophase I no chiasmata form and no crossing over occurs. If a nuclear envelope has formed during Telophase I, it is broken down. Centroiles move to opposing poles and spindle fibres start to form. 

== Metaphase II ==

The dyads align on the metaphase plate and spindle fibres attach to the kinetechores.

== Anaphase II ==

The dyads are pulled apart by spindle fibres and the myads arrive at opposite poles.

== Telophase II ==

The nuclear envelope reforms around the myads. Cytokenesis occurs and the cells divide. This leaves us with 4 unidentical daughter cells, also known as gametes. 

= References =

<references />

Haploid

2011-12-01T16:04:33Z

110097981:

A haploid cell contains only one set of [[Chromosome|chromosomes]] and therefore has only one [[Alleles|allele]] of each gene, this makes organisms made up of haploid cells good for genetic experiment because any [[Mutation|mutations]] in the genome will have to be expressed as there are no other alleles to hide behind as there would be in a [[Diploid|diploid cell]].

In humans [[Gametes|gametes]] are the haploid cells generated by [[Meiosis|meiosis]], this way when fertilization occurs the cell will have a full [[Diploid|diploid]] set of [[Chromosome|chromosomes]]. <references />

'''References'''

Hartl Daniel L., Jones Elizabeth W., (2009), ''Genetics, Analysis of genes and genomes'', 7th edition, Canada, USA: Jones and Bartlet Publishers

Haploid

2011-12-01T16:03:53Z

110097981:

A haploid cell contains only one set of [[Chromosome|chromosomes]] and therefore has only one [[Alleles|allele]] of each gene, this makes organisms made up of haploid cells good for genetic experiment because any [[Mutation|mutations]] in the genome will have to be expressed as there are no other alleles to hide behind as there would be in a [[Diploid|diploid cell]].

In humans gametes are the haploid cells generated by [[Meiosis|meiosis]], this way when fertilization occurs the cell will have a full [[Diploid|diploid]] set of [[Chromosome|chromosomes]]. <references />

'''References'''

Hartl Daniel L., Jones Elizabeth W., (2009), ''Genetics, Analysis of genes and genomes'', 7th edition, Canada, USA: Jones and Bartlet Publishers

Haploid

2011-12-01T16:02:42Z

110097981:

A haploid cell contains only one set of [[Chromosome|chromosomes]] and therefore has only one [[Allele|allele]] of each gene, this makes organisms made up of haploid cells good for genetic experiment because any [[Mutation|mutations]] in the genome will have to be expressed as there are no other alleles to hide behind as there would be in a [[Diploid|diploid cell]].

In humans gametes are the haploid cells generated by [[Meiosis|meiosis]], this way when fertilization occurs the cell will have a full [[Diploid|diploid]] set of [[Chromosome|chromosomes]]. <references />

'''References'''

Hartl Daniel L., Jones Elizabeth W., (2009), ''Genetics, Analysis of genes and genomes'', 7th edition, Canada, USA: Jones and Bartlet Publishers

Haploid

2011-12-01T16:02:16Z

110097981:

A haploid cell contains only one set of [[Chromosome|chromosomes]] and therefore has only one [[Allele|allele]] of each gene, this makes organisms made up of haploid cells good for genetic experiment because any [[Mutation|mutations]] in the genome will have to be expressed as there are no other alleles to hide behind as there would be in a [[Diploid|diploid ]]cell.

In humans gametes are the haploid cells generated by [[Meiosis|meiosis]], this way when fertilization occurs the cell will have a full [[Diploid|diploid]] set of [[Chromosomes|chromosomes]]. <references />

'''References'''

Hartl Daniel L., Jones Elizabeth W., (2009), ''Genetics, Analysis of genes and genomes'', 7th edition, Canada, USA: Jones and Bartlet Publishers

Haploid

2011-12-01T15:44:52Z

110097981:

A haploid cell contains only one set of chromosomes and therefore has only one allele of each gene, this makes organisms made up of haploid cells good for genetic experiment because any mutations in the genome will have to be expressed as there are no other alleles to hide behind as there would be in a diploid cell.

In humans gametes are the haploid cells generated by meiosis, this way when fertilization occurs the cell will have a full diploid set of chromosomes. <references />

'''References'''

Hartl Daniel L., Jones Elizabeth W., (2009), ''Genetics, Analysis of genes and genomes'', 7th edition, Canada, USA: Jones and Bartlet Publishers

Haploid

2011-12-01T15:41:04Z

110097981:

Haploid

2011-12-01T15:39:13Z

110097981:

Meiosis

2011-12-01T15:21:05Z

110097981:

Meiosis

2011-12-01T15:18:26Z

110097981:

Meiosis is a type of cell division. It can only occur in [[Diploid|diploid]] cells, resulting in four unidentical [[Haploid|haploid]] [[Daughter cells|daughter cells]]. This contrasts to mitosis which can occur in both [[Haploid|haploid]] and [[Diploid|diploid]] cells, producing only two identical daughter cells. There are two stages of Meiosis, Meiosis I and II. This leads to the nucleus diving twice but chromosome replication only occuring once. Like mitosis, chromosomes in meiosis have duplicated in Interphase, during S phase.  

= Meiosis I <ref>Hartl DL and Jones EW (2009) Genetics: Analysis of Genes and Genomes, Seventh Edition, USA, Jones and Bartlett Publishers</ref> =

Meiosis 1 is separated into 4 stages. These are Prophase I, Metaphase I, Anaphase I and Telophase I.

== Prophase I ==

During prophase I chromosomes pair, condense and crossing over occurs between non-sister chromotids. It is separated into 5 different stages. Similar to mitosis, cetrioles move to opposite poles and spindle fibres start to form. 

=== Leptotene ===

Leptotene is the first stage of Prophase I. During the Leptotene stage chromosomes coil and condense. This is whne the chromosomes first become visible.

=== Zygotene ===

During Zygotene the homologous chromosomes pair up and the [[Synaptonemal Complex|synaptonemal complex]] between the homologous chromosomes start forming.

=== Pachytene ===

Synapsis is now complete and the a [[Bivalent|bivalent]] (pair of homologous chromosomes) is formed. Chiasmata (singular: chiasma) form between non-sister chromotids of homolohous chromosomes. This is the point where crossing over occurs and DNA exchange occurs. 

=== Diplotene ===

The snaptonemal complex breaks down, allowing the chromosomes to separate. The chiasmata are now visible and are point at which the chromosomes are still held together. 

=== Diakensis ===

During diakenesis the nuclear envelope starts to breakdown. The bivalents are now ready for metaphase 

== Metaphase I ==

Bivalents or tetrads (four chromotids) align on on the metaphase plate (the equator of the cell) and spindle fibres attach to the kinetichores, protein structures located at the centromeres. 

== Anaphase I ==

Disjunction occurs. This is when the mitotic spindles pull the tetrads apart to forming dyads, which migrate to opposite poles. 

== Telophase I ==

Nuclear envelope may form around the dyads and cytokinesis (cell division) occurs. 

== Interphase ==

Interphase does not have to occur between Telophase I and Prophase II, but it can occur. Unlike traditional interphase, there is no DNA replication but growth and biosynthetic activities can still occur. 

= Meiosis II   =

During the second meiotic division the cell number stays the same before and after the division. Sometimes the cell begins prophase II straight after meiosis I has finished but there can also be a pause where the chromosomes uncoil for a while (but will never replicate). It is also important to remember there is no crossing over during meiosis II but ony during prophase I of Meiosis I.<references />

= Prophase II =

Unlike Prophase I no chiasmata form and no crossing over occurs. If a nuclear envelope has formed during Telophase I, it is broken down. Centroiles move to opposing poles and spindle fibres start to form. 

== Metaphase II ==

The dyads align on the metaphase plate and spindle fibres attach to the kinetechores.

== Anaphase II ==

The dyads are pulled apart by spindle fibres and the myads arrive at opposite poles.

== Telophase II ==

The nuclear envelope reforms around the myads. Cytokenesis occurs and the cells divide. This leaves us with 4 unidentical daughter cells, also known as gametes. 

= References =

<references />