Lesson 2: Chromosomes and Mitosis

: DNA is the chemical that gives the cell instructions and determines our traits. Chromosomes are strands of DNA (look like spaghetti)

Why do cells need to divide? Unicellular organisms need to make more of themselves when they get to be too big. Our body cells need to divide to make more of themselves to repair damaged skin, bones and other body cells.

What about the chromosomes? After mitosis, the cell has the same number of chromosomes as the parent. Therefore, the daughter cells have the same DNA as the parent cell. GENETICALLY IDENTICAL!

Below are skin cells. Talk with you partner about why it’s important for them to be EXACTLY the same as the parent after they divide.

Why is it important for cells to be exactly the same as the parent after mitosis? So that they can have the same exact structure and perform the same exact function of the old skin cells.

Is this sexual or asexual reproduction? Below is a picture of cell going through the process of mitosis. Talk with your partner about the questions below: Is this sexual or asexual reproduction? The black strands inside of the cell are called _______________ There is ______ parent cell. At the end of mitosis, there are _____ daughter cells, or offspring.

Let’s Practice: A tiger’s normal body cells have 38 chromosomes.

A tiger’s normal body cells have 38 chromosomes. Pretend the tiger got bit by an alligator and the bite broke its skin. How many chromosomes are in the parent skin cell? What process will the tiger’s cell go through to make more skin cells to repair the wound? What form of reproduction is this? Why? How many chromosomes will the new daughter skin cells have?

The alligator bite also tore some muscle What process will the tiger’s muscle cell go through to repair itself? What form of reproduction is this? Why? How many chromosomes will the new muscle cell have?

A bacteria living in the lake with the alligator is getting too big and must split into two to carry on its life processes. Is this sexual or asexual reproduction? What process will the bacteria go through to make two new bacteria? Pretend the parent bacteria had 1 chromosome, how many will the 2 new bacteria cells have?

Here is a cell from your body: After mitosis, draw what the two daughter cells should look like:

Which method (A or B) is showing asexual reproduction? ______ Describe the number of chromosomes in the daughter cells in Method A.

A pair of chromsomes is called HOMOLOGOUS KP #2: How do chromosomes exist in our normal body cells? They exist in pairs. (2) A pair of chromsomes is called HOMOLOGOUS chromosomes.

KP #3: Why do they come in pairs? One comes from _______. One comes from ______

How many chromosomes do humans have in our normal body cells? KP #4: How many chromosomes do humans have in our normal body cells? ____!