meiosis
DESCRIPTION
The process of meiosisTRANSCRIPT
![Page 1: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/1.jpg)
MeiosisStages of meiosis
by Qwabe Simphiwe
![Page 2: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/2.jpg)
What is meiosis?
Meiosis is a type of cell division. Occurs in gamete cell. There is a single DNA replication, followed by 2 nuclear
divisions. Each of the resulting daughter cells has one half of the
number of chromosomes as the parent cell.
From Diploid (2n) Haploid (n)
![Page 3: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/3.jpg)
MeiosisAlternating stageschromosome number must be reduced
diploid46 haploid232n n
humans: 46 23meiosis reduces chromosome numbermakes gametes
fertilization restores chromosome number
haploid diploidn 2n
![Page 4: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/4.jpg)
Chromosome Number• Organisms produce gametes (sex cells) that contain one of each kind of
chromosome.
• A cell with only one of each kind of chromosome is called haploid (n).
• Sex cells have one of each kind of chromosome so that when they combine (as egg and sperm do during fertilization), the resulting cell is diploid.
• Each species has a specific number of chromosomes.
• Humans have 23 pairs (46 total)
• Fruit Flies have 4 pairs (8 total)
• Dogs have 39 pairs (78 total)
![Page 5: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/5.jpg)
Human Chromosomes
• Humans have 23 pairs of chromosomes
(46 total)• 22 pairs of autosomes
• 1 pair of sex chromosomes
• Half of each pair came from one parent and half
came from the other parent
![Page 6: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/6.jpg)
Meiosis Phases
• Meiosis I– Prophase I– Metaphase I– Anaphase I– Telophase I
• Meiosis II– Prophase II– Metaphase II– Anaphase II– Telophase II
![Page 7: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/7.jpg)
THE OVERVIEWOF MEIOSIS
![Page 8: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/8.jpg)
STAGES OF MEIOSIS
Requires two divisions Meiosis I - the chromosomes of each homologous pair
separate Meiosis II - the sister chromatids of each duplicated
chromosome separate
![Page 9: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/9.jpg)
MEIOSIS 1:EARLY PROPHASE1
Chromosomes condense. Spindle forms. Nuclear envelope fragments.
![Page 10: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/10.jpg)
MEIOSIS 1: Late prophase
Homologs pair. Crossing over occurs
![Page 11: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/11.jpg)
PROPHASE 1: CROSSING OVER
Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring
![Page 12: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/12.jpg)
Crossing Over - variation
nonsister chromatids
chiasmata: site of crossing over
variation
Tetrad
![Page 13: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/13.jpg)
MEIOSIS1: METAPHASE 1
• Homologous pairs of chromosomes align along the equator of the cell
![Page 14: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/14.jpg)
MEIOSIS 1:ANAPHASE 1
Homologs separate and move to opposite poles.
Sister chromatids remain attached at their centromeres.
![Page 15: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/15.jpg)
MEIOSIS 1: TELOPHASE 1
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
![Page 16: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/16.jpg)
MEIOSIS 2:
• Meiosis II produces gametes with
• one copy of each chromosome and thus one copy of each gene.
![Page 17: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/17.jpg)
PROPHASE2
Nuclear envelope fragments.
Spindle forms.
![Page 18: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/18.jpg)
Metaphase 2
Chromosomes align
along equator of cell.
![Page 19: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/19.jpg)
Anaphase 2
Sister chromatids separate and move to opposite poles.
![Page 20: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/20.jpg)
TELOPHASE 2• Nuclear envelope assembles.
• Chromosomes decondense.
• Spindle disappears.
• Cytokinesis divides cell into two.
![Page 21: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/21.jpg)
Results of Meiosis• Gametes (egg & sperm)
form
• Four haploid cells with one copy of each chromosome
• One allele of each gene
• Different combinations of alleles for different genes along the chromosome
![Page 22: Meiosis](https://reader037.vdocuments.net/reader037/viewer/2022110302/5494e70db47959204b8b467f/html5/thumbnails/22.jpg)
references
Precious on May 28, 2013 . Meiosis in eukaryotic cells
http://www.slideshare.net/Pheshu/meiosis-in-eukaryotic-cells Accessed : 2014/03/06
Fred Phillips, Biology Teacher at Wando High School on Nov 30, 2008 . Meiosis Notes
http://www.slideshare.net/fred_phillips/meiosis-notes-presentation . Accessed : 2014/03/05
wja10255 on Feb 27, 2012 . Meiosis Notes
http://www.slideshare.net/wja10255/meiosis-notes-11773690 . Accessed : 2014/03/06
wraithxjmin on Apr 24, 2008. Lecture 6 Cell Division [Meiosis]
http://www.slideshare.net/wraithxjmin/lecture-6-cell-division-meiosis . Accessed :2014/03/06
docsawyer on Feb 05, 2010. Meiosis Notes
http://www.slideshare.net/docsawyer/meiosis-notes-3075315 . Accessed : 2014/03/06