1. Ch 10 Review & Ch 11 Meiosis Intro

2. Ch 10: Mitosis Review

3. Chromosomes
Def – the genetic information passed down from parent to offspring
Each/every human cell has 46 chromosomes
44 = non-sex chromosomes (22 pairs)
2 = sex chromosomes  X or Y (1 pair)
All body cells (except sex cells) go through mitosis
Mitosis produces cells that are:
Clones/genetically identical to parent

5. Chromosomes, cont.
Before cell division, each chromosome/DNA strand must replicate/copy itself
Occurs during S phase of Interphase
Creates two identical sister parts
Called sister chromatids
Chromatids are attached at a point called centromere

7. BEFORE chromosome replication AFTER chromosome replication

8. Cell growth and division
A cell goes through 3 distinct life stages:
1) Interphase
Growth, preparation
2) Mitosis
Nuclear division
3) Cytokinesis
Cytoplasmic division
M phase

9. The Cell Cycle Two phases of cell cycle: 1) Interphase (G1, S, G2)
Cells prepare for division
Copy/replicate DNA
Serves as a checkpoint for M phase
Cell will NOT go on to M phase unless p53 gene has proofread and detects NO problems

10. Cell cycle, cont. 2) M phase Made of two distinct phases:
A) Mitosis (nuclear division)
B) Cytokinesis (cytoplasmic division)
Four phases within mitosis:
Prophase, metaphase, anaphase, telophase
At the end, two cells produced are genetically identical to parent cells
Serves as a source of new cells as organisms grows, develops and repairs old/injured cells

11. Mitosis animation

12. Daughter cells vs. parent cells
Initial Comparison
Mitosis
Meiosis
# of cells produced 2 4
Daughter cells vs. parent cells
Identical
Not identical (Why? crossing over)
# of chromosomes
Same
(46  46 in humans)
Cut in ½ (46  23 in humans)
Purpose
To produce new cells (growth, repair old/damaged cells)
To produce gametes -egg and sperm
(for sexually reproducing organisms)

14. Ch 11: Meiosis Intro.

15. Introduction Occurs in the testes and ovaries Meiosis forms gametes
Gametes are sex cells
Gametogenesis is the production of gametes
Ex: sperm (male), egg (female)
Occurs in the testes and ovaries
Males: continually make sperm
Females: are born with all eggs (eggs form through meiosis during development)
Mitosis occurs in the REST of the animal body

16. An offspring must inherit a single copy of every gene/chromosome from EACH parent
Why?
If you inherited more, you would end up with more than 2 copies of genes/chromosomes
Three copies = genetic disorders (Down syndrome)
If you inherited less, you would end up with less than 2 copies
One copy = normally, fetus death

17. When your body forms gametes, the two original sets of genes (one from mom, one from dad) must separate
Why?
Each sperm/egg will receive ONE copy of the genes
Why only ONE copy?
When gametes combine (during fertilization), the offspring receives two copies
One from mom, one from dad

19. Chromosome Number
All animals have the same number of chromosomes in their body cells
Humans:
Body cells: 46
Sex cells: 23
Fruit fly:
Body cells: 8
Sex cells: 4
23 from MOM; 23 from DAD
4 from MOM; from DAD

20. Chromosome #, cont. In body cells, chromosomes are found in pairs
These have a special term to describe them…
Homologous chromosomes:
A partner or corresponding opposite sex chromosome (with same gene in the same location)
ONLY found in body cells
NOT found in sex cells
Why? Remember – sex cells only have ONE copy of the chromosomes

22. Diploid and Haploid Two types of cells in body: 1) Diploid
Contain two full sets of chromosomes
Humans = 46; Fruit fly = 8
One set from mom; one set from dad
Represented by “2N”
N = one set of chromosomes
Cell type: all body cells (muscle cell, red blood cell, heart cell, etc)

23. Diploid and Haploid,cont.
Contain only ONE full set of chromosomes
Humans – 23; Fruit fly – 4
Represented by “N”
Cell type: gametes (egg and sperm)
When egg and sperm combine during fertilization, the offspring (zygote) will have TWO sets of chromosomes
After fertilization…the zygote is diploid!

24. Meiosis Intro
Process of reduction division in which the number of chromosomes per cell is cut in half
Separates homologous chromosomes in a diploid cell
End result: 4 daughter cells with ½ # of chromosomes
Humans: 1 parent cell (w/ 46 chromo)becomes 4 daughter cells (w/ 23 chromo)
Diploid cell becomes haploid
Occurs in sexual organs of animals and plants
Forms gametes (sex cells)

25. Meiosis I Meiosis has two distinct phases: Meiosis I: Meiosis I
Meiosis II
Meiosis I:
Before Meiosis I, chromosomes are duplicated (in the S-phase of Interphase)
Just like mitosis!

27. Meiosis I, cont. Steps are similar to mitosis Two differences:
1) Metaphase
Mitosis: Chromosomes line-up using centromere
Meiosis: Homologous chromosomes line-up
2) Crossing over
A process that results in the exchange of alleles between homologous chromosomes
Produces new combinations of alleles
This explains why you aren’t EXACTLY like mom/dad
Mitosis: does NOT occur
Meiosis: occurs during prophase I

28. Homologous chromosome pair

29. Meiosis I, cont. Crossing over produces: Recombinant DNA
Def – DNA that is randomly changed into a different combination of genetic material
Uses homologous chromosomes
Sorts/shifts DNA through the switching of sections of chromosomes

30. Meiosis I

31. Meiosis II
Two cells produced in Meiosis I now enter into a second division (called Meiosis II)
UNLIKE Meiosis I, cells DO NOT replicate DNA before dividing
Meiosis II is identical to mitosis
Only two differences:
No Interphase before Meiosis II division
End result?? Daughter cells with ½ # of chromos
Daughter cells contain haploid set (started with diploid set)

33. Gamete Formation In animals: Male gamete  sperm
Female gamete  egg/ova/ovum
Usually only ONE gamete (per sex) is involved in fertilization
Exceptions: twins, triplets, etc.

34. Gamete formation, cont. Male gamete formation:
All 4 daughter cells become working sperm
Males produce new sperm every day

35. Gamete formation, cont. Female gamete formation:
Only 1 of 4 daughter cells become an egg
Cytoplasm (from other 3) is “stolen” by this ONE egg
Forms 3 polar bodies and 1 egg/ovum
Why?
ONE really healthy egg is formed every time!
Females produce eggs BEFORE baby is born