Mitosis and Meiosis

The continuity of life is based on the reproduction of cells, or cell

division.

Cell Reproduction

• Two types of cell division in eukaryotic cells: one called mitosis and the other meiosis

• Cell division in prokaryotic (bacteria) cells: is called binary fission

• Words of Wisdom: Understand the process, and you will understand the words.

Key Ideas

• Question: Why do cells divide?

• Question: How do cells divide?

Why don’t cells get giant?

• Remember cell membranes?– Input of nutrients and gets rid of wastes.

• Think about Geometry…volume of a cube is going to increase faster than the surface area. The cell membrane is a surface area issue.

Dividing a Eukaryotic Cell

• Example: skin cell

Skin cell

A skin cell will divide to form two skin cells. The genetic information must be the same.

• Before a cell can divide, its genetic information must be organized and it must be doubled.

Organizing Genetic Material

1. DNA

2. Chromatin – DNA wrapped around histone proteins (help maintain the shape of chromosome and aid in the tight packing of DNA)

3. Continues coiling

4. Chromosome – 2 molecules of DNA

Understanding Chromosomes

• FYI:– Chromosomes only exist during cell division– The DNA has doubled by replicating itself

How Are Chromosomes Categorized?

• Sex chromosomes – c`somes that determine the sex of an organism. For example in humans X female Y Male. Normal females have two X c`somes and normal males have an X and a Y c`some.

• Autosomes – all the other c`somes. For example in humans 44 c`somes are autosomes and 2 are sex c`somes. Total of 46 c`somes.

Homologous Chromosomes

• Homologous chromosome – two copies of each autosome produced by sexual reproduction– Same size, same shape

• For example, if one c`some in a pair of homologous c`somes contains a gene for eye color so will the other c`some in the homologous pair.

Karyotype• Karyotype – a

photomicrograph of the c`somes in a dividing cell found in a normal human. – Used to examine an

individuals c`somes.

– Made by sampling a person’s blood.

– White blood cells from the sample are treated with chemicals to stimulate mitosis.

Diploid and Haploid Cells

• Diploid – cells having two sets of c`somes. Have both autosomes (homologous c`somes) and sex c`somes.– All normal human cells, except reproductive cells (sperm and

egg cells) are diploid cells.– Abbreviated as 2n

• Haploid – human sperm and egg cells. Contain only one set of c`somes. They have half the number of c`somes that are present in diploid cells.– Human haploid cells have only one c`some of each homologous

pair and only one sex c`some.– Abbreviated as 1n– When a sperm cell (1n) and an egg cell (1n) combine to create

the first cell of a new organism, the new cell will be diploid (2n).

Key Ideas Answered

• Question: Why do cells divide?• Answer: To maintain their volume to surface

ratio.• Question: How do cells divide?• Answer: 1. The cell organizes its genetic

information and doubles it.a. Chromosomes are formed by DNA packing around histone

proteins

b. This period of the cell cycle is called Interphase where the:– Cell grows, DNA replicates, and cell prepares to divide

Examining the Eukaryotic Cell Cycle

• 90% of a cell’s life is spent in Interphase!• Interphase

Divided into three phases:G1 Phase – where cells function, cell grows in sizeS Phase – DNA is replicatedG2 Phase – where a cell can grow some more before it divides

• A cell spends only 10% of it’s life dividing! Some never divide!

• Onward to Cell Division!!!

Prophase Metaphase

Anaphase Telophase

Animal (Whitefish) Mitosis