Biology I Honors

Stages of Mitosis

Mitosis Have you every been sunburned, cut your skin or

bruised it? Thanks to mitosis and the rest of the cell cycle,

your damaged skin gets replaced! Most of your other tissues undergo cell

duplication as well. These all include mitosis as part of the process Bone tissue, muscle tissue, digestive tissue, and

some nerve tissue are included. You simply cannot go through life without Mitosis!

Mitosis Mitosis is going on throughout your entire

body Mitosis is the process of making new

cells from existing cells through the process of nuclear division

Most of the activity involves the cells chromosomes

Each cell in your body needs a full set of your chromosomes

Mitosis During cell division, the DNA breaks up

into short pieces called chromosomes Each type of organism has its own specific

number of chromosomes (and chromosomes are paired)

Example Humans have 23 pairs of chromosomes,

therefore, humans have a total of 46 chromosomes

Two of those chromosomes determine sex The others carry information about other

things like height, eye color, etc. The process of cell division can be broken

down into several steps

Step 1: Interphase DNA breaks up into short segments called

chromosomes Each chromosome “runs a copy” of itself Each pair of copies stays attached in the

middle only Extra cytoplasm is made

Step 2: Prophase Chromosomes thicken and shorten The nuclear membrane disappears, and

threadlike spindle fibers appear at the ends of the cell

Step 3: Metaphase Chromosomes line up along the middle of

the cell and each centromere is attached to a spindle fiber

Step 4: Anaphase Spindle fibers pull one chromosome from

each pair towards opposite ends of the cell

Step 5: Telophase The nuclear membrane reappears and the

cell pinches inwards in the middle Two “daughter” cells are produced

Remember… Mitosis produces all body cells EXCEPT egg

and sperm cells

Refer to your handout and label the stage of Mitosis (you may refer to page 208 in your textbook for assistance)

Meiosis Meiosis is the process by which a diploid cell

forms gametes Produces only egg and sperm cells Cells undergoing meiosis go through the same

first steps described in mitosis, except that process is called meiosis

If cells are to become egg or sperm cells, after meiosis, when there are two daughter cells, those daughter cells then undergo meiosis again

The only difference is that the chromosomes are not copied in the interphase stage

Meiosis All other stages of this second meiosis are

the same This series of divisions is called meiosis II

(2) The newly formed cells end up with half

the normal number of chromosomes If not, during fertilization when the egg

and sperm cells join, there will be twice as many chromosomes as the organism needs, and it will not survive

Meiosis Refer to your handout (page 30) and label

the stages of Meiosis (You may refer to page 215 in your textbook for assistance)

With a partner, see if you can correctly complete the handout “Comparing Mitosis and Meiosis”

Tasks to Complete With a partner, see if you can correctly

complete the handout “Comparing Mitosis and Meiosis”

Experiment 6.2: Mitosis – Follow the instructions for that experiment - you will need to draw and color what you see!