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: G 1 Phase – where cells function, cell grows in size S Phase – DNA is replicated G 2 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!!!

ProphaseMetaphase AnaphaseTelophase Animal (Whitefish) Mitosis