Cell Division (Continued)

Revision of Mitosis and Introduction of MeiosisBC Science Probe 9

Section 3.1Pages 74-78

Cell division

• There are two types of cell division:

– Mitosis

– Meiosis

Cell Division

• What do you remember about cell division and mitosis from before Spring Break?

Mitosis• One cell splits into two identical daughter

cells (cloning)

What are found in cells and contain the genetic information?

• Before the cell can divide the chromosomes have to be copied

Why do you think this is important?

• If the chromosomes weren’t copied then each new cell would have half the normal number

http://cellsalive.com/mitosis.htm

What is mitosis for?• Mitosis is used to produce new body

cells (eg. for growth and repair).• Simple plants and animals can also

use mitosis to reproduce• This is called Asexual reproduction

What happens in mitosis?1. The chromosomes get thicker

What happens in mitosis?

2. The chromosomes are replicated and can now be seen as x-shapes

What happens in mitosis?

3. The nuclear membrane disappears. The chromosomes line up on the spindle. The chromosomes are pulled to opposite ends of the cell

What happens in mitosis?

4. Each new cell is IDENTICAL to the original and has THE SAME number of chromosomes (diploid number = 2n)

How much can you remember?

• Answer the following questions as quickly as you can

• Each question will be displayed for 10 seconds. . .

Question 1

• If a cell with 28 chromosomes divides into

2 new cells, how many chromosomes will

each new cell have?

Question 2

• True or False . . .

The cells produced in mitosis are

genetically identical

Question 3

• True or False . . .

Bacteria reproduce using mitosis

Question 4

• True or False . . .

Sperm are produced by mitosis

Question 5

• True or False . . .

It is possible for a female green fly to

reproduce using mitosis

Answers

1.28

2.True

3.True

4.False - sperm are produced by meiosis

5.True - this process is called parthenogenesis

Meiosis

What is Meiosis?

• Meiosis is a special type of cell division used to make sex cells (gametes)

• Gametes need to have half the ordinary number of chromosomes (haploid number = n)

• Regular cells have the ordinary number of chromosomes which is called diploid = 2n.

What are the sex cells in humans called?

http://cellsalive.com/meiosis.htm

• This means that when they fuse together during fertilization the zygote has the same number of chromosomes as the parents’ cells

Why do you think this is important?

Why is meiosis important?• The new cells are all different because the

chromosomes get shuffled – each egg or sperm only has half the parents chromosomes and which half is random

• So if there are 23 pairs of chromosomes there are 223 possible combinations (in other words a huge number)

• The important things to remember about meiosis are that it promotes variation within a species and maintains the correct chromosome number

Formation of gametes

46

46

23 23

How many chromosomes here?

What happens in meiosis?

1. The chromosomes become visible and get thicker

What happens in meiosis?

2. The chromosomes are replicated and can now be seen as x-shapes

What happens in meiosis?

3. The nuclear membrane disappears. The chromosomes line up in homologous pairs in the middle of the cell along the spindle

What happens in meiosis?

4. The pairs of chromosomes separate and are pulled to opposite ends of the cell along the spindle

What happens in meiosis?

5. The cell splits into two, each cell gets 1 chromosome from each pair

What happens in meiosis?7. Chromatids separate. Each cell splits into two

and nuclear membrane reappears

What happens in meiosis?8. Each new cell is DIFFERENT to the original and

has HALF (n) the original number of chromosomes

The interchange of some genesMeans:1. The gametes produced carry different combinations of

genes2. They do not have the same combination as the parent cell

3. They do not have the same combination as each other

GAMETESPARENT CELL

Parent Cell Chromosome #

Sister Chromatids…

# of Daughter Cells

# of Chromosomes

in Daughter Cells

Mitosis 2n Separate during anaphase 2 2n

Meiosis 2nStay together in

meiosis I, but separate during

meiosis II4 n

Assignment

• Complete the table cell division handout.