Introduction to Cell division

CELL DIVISION

Mitosis and Meiosis

DNADNA is the molecule that stores hereditary or genetic information inside a cell and transmits it to other cells during cell division

Below you can see a model of the double helixdouble helix shape of DNA:

When a cell is dividing, DNA winds up tightly and forms chromosomeschromosomes in the nucleus of the cell.

The specific portion of the DNA code with genetic information to synthesize a protein is called a genegene. Genes are contained within the chromosomes.

A karyotype is a picture showing the arrangement of a full set of human chromosomes.

Humans have 46 (or 23 pairs of) chromosomes

Animal Somatic Cells (cells of the body) are diploid. This means that each cell has two chromosomes of each type. They are in PAIRS.

Gamete cells (egg, sperm) are haploid. This means that each cell has only one of each type of chromosomes.

Biologists use “2n” to symbolize diploid and “n” to symbolize haploid.

MITOSIS: When somatic (body) cells reproduce themselves the process is called MITOSIS. All somatic cells are diploid (2n) and both daughter cells produced are also diploid.

Mitosis leads to the production of two “daughter cells”. Each daughter cell has the same number of chromosomes as the parent cell:

A somatic Cell 2n Two Daughter Cells 2n

INTERPHASE - DNA replicates

PROPHASE - diffuse chromatin condenses into discrete chromosomes

PROMETAPHASE - chromosomes move toward the “equatorial plane”

METAPHASE - chromosomes are lined up at the equatorial plane (also called the metaphase plate)ANAPHASE - Sister chromatids disjoin and migrate to opposite poles.TELOPHASE - chromosomes decondense and a cleavage or furrow begins to form in the middle of the cell. Finally, the cell divides into two: this is called cytokinesis.cytokinesis.

The steps of Mitosis:The steps of Mitosis:

MEIOSISThe process that form gametes (sperm or egg) is called MEIOSISMEIOSIS. During meiosis, a single diploid cell divides and produces FOUR haploid reproductive cells.

n

2n

n

Mother cell

n n

In Meiosis there is one chromosome duplication followed by two cellular divisions (into four cells) so Meiosis comprises two stages: Meiosis I and II.

n eggn sperm

Through fertilization, an n sperm joins with an n egg and form a 2n zygote .

2n zygote

Gamete Cells

The steps of Meiosis I

The steps of Meiosis II:Meiosis II:

What is the MAJOR difference between these two processes?MITOSISMITOSIS keeps the same chromosome number :

2n 2n

Whereas MEIOSIS MEIOSIS halves the chromosome number:

2n n

And Crossing Crossing overover that only occurs during meiosis and originates

recombinant recombinant cromosomescromosomes

This way most gametes are different, which has lead living beings to variability

Any questions?

Thanks for your attention

Adapted from:

http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookDNAMOLGEN.html

http://edweb.sdsu.edu/ltca/Mitosis_Meiosis_files/frame.htm#slide0001.htm

by: Christianna Antonello