Cell Division

DNADNA – large molecule that stores

hereditary (genetic) information.- found in the nucleus of a cell.

- controls cell division.

ChromosomesChromosomes – MANY strands of

DNA wound together into threadlike structures.

Cell DivisionCell Division – a cell that is dividing into

two new cells.

- the two new cells are daughter cells.

MitosisMitosis – two daughter cells with exact

same genetic material (DNA) are produced.

- daughter cells have same number of chromosomes as parent cell.

6 chromosomes 6 chromosomes

6 chromosomes

InterphaseInterphase – preparation stage BEFORE

Mitosis where the cell grows and duplicates materials.

- Longest stage of Cell Cycle

- Copies chromosomes!

- Organelles double.

ProphaseProphase – first phase of Mitosis where

DNA winds into chromosomes.

Prophase

Chromosomes

Metaphase

Metaphase – chromosomes line up along the middle of the cell.

Metaphase

Chromosomes

Middle (equator) of cell

Anaphase

Anaphase – chromosomes are “pulled” apart!

- move to opposite sides of cell.

Anaphase

Single Chromosome

Telophase

Telophase – “ending” phase of Mitosis.

- two new cells form.

Telophase

New nuclei

Chromosomes unwinding

End Results of Mitosis

4 chromosomes at start

Chromosomes double into 2 strands (8)

4 chromosomes in each new cell at end

What kinds of cells do Mitosis?Single-celled organisms - mitosis as a

form of asexual reproduction.

Multicellular organisms - mitosis in repair and replacement of body cells (hair, skin, etc.)

Cancer: Uncontrolled DivisionNormal cells will stop dividing when they

come in contact with other cells.

Cancer – disease where cells do not stop dividing and ignore signals from other cells.

What is the Purpose of Reproduction?

To form new individuals (offspring) of a species.

2 Types:

1. Asexual Reproduction – reproduction involving only one parent.

2. Sexual Reproduction – reproduction involving two parents.

Asexual Reproduction

Offspring are identical and contain same amount of genetic material as parents.

- Results from mitosis.

Ex: a. Budding

b. Binary Fission

c. Vegetative Propogation

d. Sporulation

e. Regeneration

Sexual Cell Division: Meiosis

Chromosome NumberHuman body cell – 46 chromosomes

Arranged in 23 pairs (23 X 2=46).

Homologous Chromosomes – a pair of chromosomes with

same size, shape, etc.

DiploidDiploid – body cells that contain two sets

of chromosomes.

- Ex: skin, hair, heart, liver, muscle cells, etc.

- Written as 2n.

HaploidHaploid – gamete (sex) cells which

contain only one set of chromosomes.

- Ex: sperm/egg cells.

- Written as n.

MeiosisMeiosis – type of cell division used to

produce gametes (sex cells).

Two functions:1. Forms cells with half the number of

chromosomes. (23 chromosomes in both egg and sperm)

2. Rearrange chromosomes for genetic differences from parents (variability).

3. Two sets of phases whereas Mitosis only has one set.

Meiosis Overview

4 Chromosomes

2 Chromosomes in each cell

Meiosis in MalesMeiosis in males produces four sperm

(n) cells which are all functional.

2n

n

n

n

n

Meiosis in FemalesMeiosis in females produces four egg (n)

cells. Only one is functional!

2n

n

n

n

n

Meiosis = Genetic VariationMeiosis is responsible for genetic

differences in new cells:

1. Chromosomes lineup in different ways.

2. Crossing over – swapping pieces of chromosomes.

Mitosis Vs. Meiosis

Mitosis Meiosis

# of parent cells 1 2

# of cells produced 2 4

Appearance of Identical Different

offspring

Types of cells Body Gametes

(egg/sperm)

Meiosis I

Interphase I – DNA is unwound as chromatin.

- DNA duplicates.

Prophase I –chromosomes become visible and double-stranded.

- Homologous chromosomes pair up.

- Crossing over – pieces of chromosomes are swapped.

Homologous chromosomes

Homologous chromosomes

Meiosis I

Metaphase I –pairs of homologous chromosomes lineup in the middle of the cell.

Anaphase I – homologous chromosomes separate (not into single-stranded chromosomes or chromatids).

Telophase I – two haploid daughter cells are formed.

- nuclear membrane

returns!

Meiosis II (like Mitosis)

Prophase II – two haploid daughter cells now enter meiosis II.

- cell has completely divided and chromosomes are separated.

Metaphase II – chromosomes (non-homologous) line up in the middle of each cell.

Anaphase II – double-stranded chromosomes split into single-stranded chromosomes (chromatids).

Telophase II – four haploid cells are formed each with single-stranded chromosomes (chromatids).