Mitosis and Meiosis

(Chapter 9)

• DNA replicates in order to go through mitosis OR meiosis

• (this has nothing to do with transcription and translation that is done to make proteins)

Cell replication

The Cell Cycle-- Interphase and Mitosis - occurs in somatic (body) cells

• when a cell is not engaged in mitosis and involved in metabolic activity and growth

• DNA is replicated• chromosomes are “invisible” under a light

microscope

Interphase

Mitosis• http://highered.mcgraw-hill.com/olc/dl/120073/bio14.swf• to grow in size all of the cells must undergo cell

division• mitosis occurs to grow and repair cells• some cells once fully formed do not undergo

mitosis, such as nerve cells• although errors in mitosis are rare, the process

may go wrong, especially during early cellular divisions in the zygote (could be really bad)

interphase mitosis

Meiosis- occurs in germ (sex- sperm and egg) cells

• http://highered.mcgraw-hill.com/olc/dl/120074/bio19.swf• in humans, except for sex cells, every cell is diploid– it has two sets of chromosomes (one from mom, one from

dad)• during the formation of gametes (egg or sperm), the

number of chromosomes is reduced by half (haploid)– occurs in the testes of males to make sperm and the

ovaries of females to make eggs

• causes a change in the genetic information to increase diversity in the offspring by the following:– 1. Crossing Over in Meiosis: The chromosomes you receive

from your mom's egg and your dad's sperm are NOT the same chromosomes that your mom and dad have. They are new, 'shuffled' versions of their chromosomes - and you only get ONE of them from each parental unit....

– 2. Independent Assortment in Meiosis: chromosomes line up or "shuffle" randomly on the metaphase. With 23 chromosomes assorting independently, there are 2^23, or 8 million, possible assortments of chromosomes inherited for every cell!

• 3. Random Fertilization: The ovum has 8 million possible chromosome combinations, so does the sperm cell. 8 million x 8 million = 64 trillion possible combinations in EACH AND EVERY zygote! WOW!!

• http://highered.mcgraw-hill.com/olc/dl/120074/bio17.swf