1. Meiosis

2. Think, Pair, Share Time Refresh my memory on Mitosis
Turn to your neighbor and discuss. Be prepared to share your responses.
What is the end product of Mitosis?
Answer: 2 identical daughter cells

3. Think, Pair, Share Continued
How many phases are there in Mitosis?
Answer: 4!
How many pairs of chromosomes do human beings have?
Answer: 23 pairs (or 46 individual)
Why are our chromosomes arranged in pairs?
Answer: because 1 comes from mom & 1 from dad

4. Recall Mitosis Results in 2 daughter cells Process has 4 stages
prophase, metaphase, anaphase, telophase and cytokinesis
Humans have 23 PAIRS of chromosomes

5. Remember: IPMAT!

6. Can that be right!?!?!
If the end result of mitosis is two identical daughter cells, then when a male gamete(sperm) and a female gamete(egg) come together during fertilization there must be 92 chromosomes!!!
Mom (23 pairs) + Dad (23 pairs) = Baby with 46 pairs!!!!

7. Meiosis!
Meiosis is a second round of cell division that separates sister chromatids in sex cells allowing the offspring to have the same number of chromosome pairs as their parents!
Males: Sperm
23 chromosomes
Females: Egg
23 chromosomes

8. Half from Dad, half from Mom combine in offspring for 23 PAIRS!

9. More on Meiosis
Meiosis allows offspring to have the same number of chromosomes as the parents (not doubled!)
Meiosis produces gametes.
Male gametes = sperm
Female gametes = egg
Gametes have ½ the number of chromosomes as the parents, so when they come together in fertilization, the offspring has 23 pairs of chromosomes.
Meiosis has 2 stages of division, not just 1 like in mitosis.
Meiosis does NOT produce identical cells

10. Chromosome Details
Chromosomes are in pairs: 1 from mom & 1 from dad. The picture below shows 2 pairs of homologous chromosomes.
This term means that the pair has genes for the same traits (in the same order)

11. Talking like a scientist…scientific vocabulary.
Haploid: cell containing one of each kind of chromosome (n)
Diploid: cell with 2 of each kind of chromosome (2n)

12. Turn notes over! No peeking!
Quick!
How many individual chromosomes do humans have? 46
A chimpanzee has a diploid number of 48, what is its haploid number? 24

13. Alleles
Our traits, (hair color, eye color, height, etc.), are controlled by genes which are located on our chromosomes.
Genes exist in alternate forms – We call these different gene forms alleles.
Allele Example: short/tall, brown/blonde, etc.

14. Crossing-over
Crossing over results in the exchange of genetic material between homologous chromosomes. Thus increasing the genetic variation in the offspring or babies.

15. Crossing over results in the exchange of genetic material.

16. Independent Assortment
The random distribution of chromosomes during meiosis results in millions of different gametes.
This independent assortment produces millions upon millions of possible combinations of gametes for fertilization between sperm and egg.

18. Foundational Facts Recall from mitosis:
IPMAT =interphase, prophase, metaphase,anaphase, telophase
Chromosome: tightly wound DNA
Sister Chromatids: two halves of the doubled chromosome structure

19. Meiosis Overview

20. Mitosis vs. Meiosis
The first five stages of meiosis look identical to mitosis…however it is the further separation of chromosomes that result in haploid gametes.

21. Mitosis vs. Meiosis Create which cells: Somatic (Body) Cells
Sex Cells (Gametes)
Result in # of Chromosomes
46 Chromosomes
23 Chromosomes
Haploid or Diploid?
Diploid
Haploid
2 identical daughter cells (46 chromosomes each)
Final Result:
4 Gametes (23 chromosomes each)

22. Problems in Meiosis
Nondisjunction: when homologous chromosomes do not separate normally
Can produce a gamete with an extra chromosome
Can produce a gamete that is missing a chromosome
Example: Down Syndrome (47 chromosomes)

23. Polyploidy
                                                                                
Organisms with more than the usual number of chromosome sets.
Very rare – usually results in death in animals
Common in agriculture!