Meiosis reduces the number of Chromosome sets from diploid to haploid

Firsts 4 Stages of Meiosis First 4 steps

First 4 stages Interphase1. Chromosomes replicate during S

phase but remain uncondensed, each replicated chromosome consists of two genetically identical sister chromatids.

2. Centrosome replicates forming two centrosomes.

The First 4 Stages Prophase I1. 90% of the time required for meiosis2. Chromosomes begin to Condense3. Line up gene by gene4. They cross over (red and the blue)5. The crisscross regions, Chiasmatas,

hold the chromosomes in place until anaphase I. (tetrads)

The First 4 Stages Metaphase I1. Chromosomes line up on the

metaphase plate, with one chromosome on either side.

2. Chromatids are attached to kinetochore microtubules from one pole.

The First 4 Stages Anaphase I1. Chromosomes move toward the poles2. Homologous chromosomes move to

opposite poles. Telophase and Cytokinesis1. They split like normal, with the

homologous chromosomes in the different sister cells.

2. (animal/plant)

Meiosis II

Meiosis II Prophase II 1. Spindle apparatus forms, Chromosomes

move toward metaphase plate Metaphase II1. Chromosomes on the metaphase plate2. NO CRISSCROSS, two sister cells are not

genetically the same3. Kinetochores attach to microtubules.

Meiosis II Anaphase II1. Centromeres finally separate2. Sister Chromatids of each chromosome

now move as two individual chromosomes toward opposite poles.

Telophase II and Cytokinesis1. Nuclei forms, Makes 4 daughter cells

and each one is genetically different from all the rest.

Comparing Mitosis to Meiosis

Mitosis Produces identical

cell as there parent.

Meiosis Reduces # of Chromosomes

sets from 2 diploid to one haploid.

Produces different cells than parent and other daughter cells.

Synapsis and Crossing over (synapsis is the process of the chromosomes crisscrossing)

Tetrads on the Metaphase plate (Tetrads is the crossover region makes an X)

Separation of homologues

Genetic Variation produced in Sexual life cycles contributes to evolution Species that reproduce sexually, the

behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation.

There are 3 mechanisms that contribute to the genetic variation

– independent assortment of chromosomes

- crossing over - random fertilization

Independent assortment of Chromosomes Metaphase I, when the homologous pairs, one is

maternal and one is paternal chromosome(mother and father), and is put on the plate.

There is a 50-50 chance on which side will be on what. When it splits into the 2 daughter cells its called independent assortment.

Each cell represents one outcome of all possible combinations of maternal and paternal chromosomes.

*Humans - 46 chromosomes, 23 combinations or 2 X 23rd power = 8 million combinations

Crossing Over Recombinant chromosomes- individual

chromosomes that carry genes(DNA) derived from 2 different parents. ^ that is a result from crossing over.

The crossover just produces new combinations of maternal or paternal genes.

Humans cross over 1 to 3 times on each chromosome.

Random fertilization Adds more genetic variation arising form

meiosis. The fusion of a single male gamete with

a female one will produce a zygote with a about 64 TRILLION diploid combinations!

Truly unique combination of genes

Evolutionary Significance of Genetic Variation Within Populations

Natural Selection, individuals best suited to the local environment leave there genes.

Leads to accumulation of those genetic variations favored by the environment

SONGS! http://www.youtube.com/watch?v=iCL6d

0OwKt8 http://www.youtube.com/watch?v=LOCa

SUZOFLA

Song Lyrics When they see us up on youtube they say cell mates really killin it First we drop mitosis now we putting out another hit Mitosis got fame pretty quick , but this ones gonna fasta In the first process a cell was split, and this is like a relative Call this one a relative? Yeah its a relative They do the same thing basically, like they in a family Whats double of mitosis? How do sex cells duplicate? Everybody knows the answer, meiosis without mistake If you all dont understand, yeah I guess we will explain Did a little research and cell split experts we became Then after we make the rap, intelligent we will remian Cause when it comes to science raps, you know the cell mates

run the game!

Same thing, same stuff, just mitosis doubled up Prophase, metaphase, same process from the last dub Anaphase, telophase, its the reason your alive No sexual reproduction, life on earth would simply stop After interphase, before its all split across Chromosomes have to break, this is known as first prophase Crossing over then occurs, genetic code forever wrote Spindle fibers pull away, the mother cell forever broke Phase 1 is now complete, lets put the process on repeat DNA dont duplicate, chromos align at center plate The two new cells divide and then, this thing happens over

again Meiosis was a success, 4 daughter cells is all thats left

I feel like in meiosis it is quite like Mitosis cept that it does this whole thing twice I feel like most students dont know this process So Ill explain it to you all with optimal finesse Its got homologous pairs, and you know they split But remaining intact are sister chromatids First, second telophase the cell begins to split into two pieces They release, just at least after cytokinesis When you let your sex cells go You wont ever have to wonder if theyre gonna regrow Cause you know with meiosis they will always restore Happens in everyone so Meiosis is hard to ignore Twenty-three chromos there, homie, in each daughter cell, homie You can ask Mr. Waggoner anaphase centromeres divide Centromeres divide Now its meiosis right (meiosis right) Its reproduction time (reproduction time) Now you know this rhyme (know this rhyme) Cause with every line, every line I put on

Works cited http://www.google.com/imgres?

um=1&hl=en&safe=off&biw=1440&bih=817&tbm=isch&tbnid=pv_7YoYp_K0mGM:&imgrefurl=http://gabrielarogers.blogspot.com/2011_03_01_archive.html&docid=cTx3L2v5dKIYSM&imgurl=http://3.bp.blogspot.com/-6VECSMU10HY/TY-RXY-t24I/AAAAAAAAAEg/Q0qe4erqknw/s1600/independent_assortment.jpg&w=800&h=551&ei=D6G4Tt_FGYimsQL_xfSxCA&zoom=1&iact=hc&vpx=390&vpy=155&dur=583&hovh=186&hovw=271&tx=155&ty=101&sig=109748501573580030227&page=1&tbnh=136&tbnw=197&start=0&ndsp=24&ved=1t:429,r:1,s:0

http://www.google.com/imgres?um=1&hl=en&safe=off&sa=X&biw=1440&bih=817&tbm=isch&tbnid=56FK40XoecaQbM:&imgrefurl=http://faculty.irsc.edu/FACULTY/TFischer/bio%25201%2520files/bio%25201%2520resources.htm&docid=E_O4XayU0bbXjM&imgurl=http://faculty.irsc.edu/FACULTY/TFischer/images/meiosis%2525202.jpg&w=800&h=507&ei=c6W4TpOFEMePsQL19_XcCA&zoom=1&iact=hc&vpx=604&vpy=156&dur=345&hovh=179&hovw=282&tx=118&ty=90&sig=109748501573580030227&page=1&tbnh=127&tbnw=201&start=0&ndsp=26&ved=1t:429,r:2,s:0

http://www.google.com/imgres?um=1&hl=en&safe=off&biw=1440&bih=817&tbm=isch&tbnid=9rfWawdXn1i50M:&imgrefurl=http://course1.winona.edu/sberg/241f08/Lec-note/Meiosis.htm&docid=br1g6Va8SmQTjM&imgurl=http://course1.winona.edu/sberg/ILLUST/Fig13-6.gif&w=750&h=337&ei=iqW4TqXkJOGIsAKS9YHFCA&zoom=1&iact=hc&vpx=966&vpy=206&dur=123&hovh=150&hovw=335&tx=144&ty=68&sig=109748501573580030227&page=1&tbnh=82&tbnw=182&start=0&ndsp=31&ved=1t:429,r:6,s:0