Meiosis Sexual Reproduction (two parents)

What is the advantage of sexual reproduction? Genetic Variation

3 things that contribute to genetic variation Independent assortment Crossing Over Random Fertilization These two processes occur during meiosis

Why Meiosis? Meiosis -the process that creates the sex cells (sperm & egg cells) called gametes, the final result are cells with ½ the total chromosomes (23 instead of 46) Meiosis is the production of sex cells (gametes). During meiosis, the number of chromosomes in the daughter cells are reduced from the number of chromosomes in the parent cell (this is extremely important).

How does Meiosis Occur? Animation of meiosis to use as a review Meiosis Animation from http://biology.clc.uc.edu/courses/bio104/meiosis.htm

Is there anything that can wrong during meiosis? Yes! It is called nondisjunction. Chromosomes don’t separate properly and some gametes end up with too many or not enough chromosomes.

What happens if nondisjunction occurs? The gamete will die or result in conditions known as trisomy or monosomy. Trisomy - a person has more than 2 copies of the same chromosome. Monosomy – a person only has one copy of a chromosome.

How can you tell that? Take a picture of the chromosomes! This is known as a karyotype.

Female Karyotype

Male Karyotype

Karyotype-Trisomy #21 Down’s Syndrome

Fertilization Mom Dad 23 46 New Individual 23 Formation of a new individual through the union of parent cells The number of chromosomes are animated so you can ask students the answers before it comes up New Individual 46

This is how new organisms are made!!

Meiosis Review How many chromosomes are in the beginning parent cell (23 or 46)? 2. How many are in the resulting gamete cells (23 or 46)? Questions are animated so you can ask each question and get an answer before going to the next question.

More Meiosis Review 3. How many gamete cells are produced? Are the resulting gamete cells different from the parent cell?

More Meiosis Review 5. Are the resulting gamete cells different from each other? 6. How many chromosomes are in a human parent cell? Questions are animated so you can ask each question and get an answer before going to the next question. 7. How many chromosomes are in a human gamete cell?

More Meiosis Review 8. What types of cells are produced by meiosis? Gametes (Sperm & Egg)

Let’s review Mitosis & Meiosis

Mitosis vs. Meiosis √ √ √ √ √ √ Event Mitosis Meiosis Produces 4 cells   Mitosis vs. Meiosis Event Mitosis Meiosis Produces 4 cells Produces 2 cells New cells identical New cells different New cells have the same number of chromosomes as parent New cells have fewer chromosomes than parent √ √ √ √ The answers are animated so you can have students answer the question before you reveal the answer. √ √

Mitosis vs. Meiosis √ √ √ √ √ Event Mitosis Meiosis   Mitosis vs. Meiosis Event Mitosis Meiosis Beginning cells 46 chromosomes Beginning cells have 23 chromosomes Ending cells have 46 chromosomes Ending cells have 23 chromosomes Produces egg and sperm Produces body cells (autosomes) √ √ √ The answers are animated so you can have students answer the question before you reveal the answer. √ √