1. Cell Division
Meiosis

2. Chromosome Number of Different Species
Homo sapiens (human) 46
Mus musculus (house mouse) 40
Zea mays(corn or maize) 20
Drosophila melanogaster (fruit fly) 8
Xenopus laevis (South African clawed frog) 36
Caenorhabditis elegans (microscopic roundworm) 12
Saccharomyces cerevisiae (budding yeast) 32
Canis familiaris (domestic dog) 78
Arabidopsis thaliana (plant in the mustard family) 10
Muntiacus reevesi (the Chinese muntjac, a deer)
Muntiacus muntjac (its Indian cousin) 6
Myrmecia pilosula (an ant) 2
Parascaris equorum var. univalens (parasitic roundworm)
Cambarus clarkii (a crayfish)
200
Equisetum arvense (field horsetail, a plant)
216

3. Chromosome Vocabulary
DNA
Doubles during interphase (S phase)
Chromosome
Forms during prophase
Become sister chromatids

4. Homologous Chromosomes:
Members of a pair of chromosomes
One – Mom
One – Dad
Same size
Same shape (centromere location)
Same number and type of genes

5. Homologous Chromosomes:
Specific gene information may differ
(brown eyes from mom, blue eyes from dad)

6. Homologous Chromosomes:
Same banding pattern when stained and viewed under a microscope.
Bands DO NOT indicate genes.

7. Types of Chromosomes:
Humans have 23 pairs of chromosomes.

8. Types of Chromosomes: 2 Types: Autosomes:
Members of chromosome pairs #1-22.

9. Types of Chromosomes: 2 Types: Sex Chromosomes:
Members of chromosome pair #23
Females = XX
Males = XY

10. Sex Chromosomes
ALL pairs are homologous in females because they have two X chromosomes
The sex chromosomes of males are NOT homologous, they have one X and one Y

11. Diploid vs. Haploid Diploid: two sets of chromosomes
Each chromosome has a homologous pair– there is one from each parent!
They have the same type of genes but are not identical
Human body cells:
23 PAIRS  46 total

12. Diploid vs. Haploid Haploid: one set of chromosomes
Why would you want just one set of chromosomes in a cell?
SEXUAL REPRODUCTION!
Human gametes: 23 total

13. Why do we need meiosis?
Meiosis is necessary to halve the number of chromosomes going into the sex cells
Gametes are haploid (1n) +
1 N sperm
1 N egg
2N zygote

14. Why do we need meiosis? + Fertilization
Male and female sex cells will provide ½ of the chromosomes each
Offspring has genes from both parents
1n + 1n = 2n +
1 N sperm
1 N egg
2N zygote

15. Video Clip
Worksheet 17: Meiosis Overview

16. Meiosis Summary Two divisions - Meiosis 1:
- like mitosis, but not quite
- creates 2 cells (haploid)
- Meiosis 2:
- divides again
- creates 4 gametes (haploid)

17. Meiosis Summary Parent cell – chromosome pair Chromosomes copied
1st division - pairs split
2nd division – produces 4 gamete cells with ½ the original # of chromosomes

18. Meiosis I – Prophase I
Nuclear envelope dissolves

19. Meiosis I – Prophase I Tetrads form Crossing Over
Homologous pair links together
Crossing Over

20. Crossing Over in Prophase I
Homologues break at identical locations,
Rejoin opposite partners
Occurs randomly several times on every chromosome
Results in mixing of the genes you inherited from your parents
Crossing over is NOT a mutation

21. Meiosis I – Metaphase I Tetrads line up in middle
Spindle fibers attach
Independent Assortment

22. Independent Assortment Metaphase I
Principle of Independent Assortment—Genes for different traits (on different
chromosomes) can separate independently of each other.
--Happens because homologous pairs line up in random order on random sides
during Metaphase I

23. Meiosis I – Anaphase I Fibers pull homologous chromosomes apart
Sister chromatids are still connected!
(2 X’s are separating from each other)

24. Meiosis I – Telophase I Cell separated into two cells
Nuclear membrane forms

25. Meiosis II – Prophase II
Nuclear membranes dissolve
New spindle fibers form

26. Meiosis II – Metaphase II
Sister chromatids connect to spindle fibers
Line up in the middle

27. Meiosis II – Anaphase II
Sister chromatids separate

28. Meiosis II – Telophase II
Cells divide
Now there are 4 haploid cells!

29. Meiosis I
Meiosis II

30. Steps of Meiosis I and II

31. Video Clip
Worksheet 18: Animal Cell Meiosis

33. Cell Division Products of Mitosis: Two identical cells Somatic cells
AKA body cells
Diploid
Products of Meiosis:
Four different cells
Gametes
AKA sex cells
Haploid

34. Comparing Meiosis and Mitosis

35. Your Turn!
Mitosis and Meiosis Worksheet