Cell Division (Continued) Revision of Mitosis and Introduction of Meiosis BC Science Probe 9 Section 3.1 Pages 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 http://cellsalive.com/mitosis.htm • 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
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 • 28 • True • True • False - sperm are produced by meiosis • True - this process is called parthenogenesis
What is Meiosis? http://cellsalive.com/meiosis.htm • 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?
Why do you think this is important? • This means that when they fuse together during fertilization the zygote has the same number of chromosomes as the parents’ cells
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
PARENT CELL GAMETES • The interchange of some genes • Means: • The gametes produced carry different combinations of genes • They do not have the same combination as the parent cell • 3. They do not have the same combination as each other
Assignment • Complete the table cell division handout.