MitosisCell division/ cell productionWhat kind of cells?Nerve, skin, epithelial, etc.- somaticSame / all the time Mitosis is reproduction in which cells
produce identical replicasOrganic growth of tissues, fibers, and
membranes
MEIOSIS
MeiosisMeiosis occurs in sexual reproduction
when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg).
MeiosisThe genetic code of a human contains 46
chromosomes
Half of this number is in egg and sperm
Divided twice which turns out 4 cells (gametes)
Each of these will have only half of the number of chromosomes; but each will contain genetic info from each parent
Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells 2 4
Genetically identical? Yes No
Chromosome # Same as parent Half of parent
Where Somatic cells Sex cells
When Throughout life At sexual maturity
Role Growth and repair Sexual reproduction
http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related
Interphase I Cells undergo a round of DNA replication
forming duplicate chromosomesEach chromosome has two sister chromatids
held together by a centromere
Prophase IChromosomes coil up and
spindle formsEach chromosome pairs
with its corresponding homologous chromosome to form a tetrad
Crossing over may occur when chromatids exchange genetic material
Crossing over results in new combinations of alleles on a chromosome
Crossing Over
Metaphase I The centromere of
each chromosome becomes attached to a spindle fiber
Spindle fibers pull the tetrads to the equator of the spindle
Homologous chromosomes are lined up side by side as tetrads
Anaphase IThe fibers pull the
homologous chromosomes toward opposite end of the cell
Centromeres do not split
This ensures that each new cell will receive only one chromosome from each homologous pair
Telophase IThe spindle breaks
down and the chromosomes uncoil
The cytoplasm divides to yield two new cells
Each cell has half the genetic info of the original cell because it has only one homologous chromosome from each pair
Prophase II Meiosis I results in two haploid (N) daughter
cells, with half the number of chromosomes as the original cell
A spindle forms in each of the two new cells and the fibers attach to the chromosomes
Metaphase II The chromosomes
line up in a similar way to the metaphase stage of mitosis
The chromosomes are pulled to the center of the cell and line up randomly at the equator
Anaphase IIThe centromere of
each chromosome splits
The sister chromatids separate and move toward opposite ends of the cells
Telophase IINuclei re-formThe spindles breakdownThe cytoplasm divides
Meiosis IIMeiosis II results in four haploid (N) daughter
cells.Each haploid cell contains one chromosome from
each homologous pairHaploid cells will become gametes transmitting
genes to off spring
What Meiosis is About
Meiosis allows the creation of unique individuals through sexual reproduction.