1. Chromosomes and Meiosis Unit

2. Cell Types 1) Somatic Cells (aka: body cells) - are diploid (2n)
- DNA not passed on

3. Cell Types 2) Gametes (aka: sex cells)
- ex: ova (egg) and spermatozoa (sperm)
- are haploid (1n)
- DNA passed on

4. Egg and Sperm Comparative Size

5. Diploid vs. Haploid
Diploid cells have two copies of each chromosome: one copy from the mother and one from the father.
Haploid cells have only one copy of each chromosome

6. Look at the following chromosome numbers of these living things.
Do you notice anything about the numbers?

7. Chromosome Numbers of Various Living Things
Algae
148
Cow 60
Dog 78
Earthworm 36
Kangaroo 12
Mosquito 6
Pigeon 80
Tiger 38
Shrimp
254
Deer 70
Turkey 82
Horse 64
Hedgehog 90
Giraffe 62
Cabbage 18
Carp
104

8. Chromosomes
Each species has a characteristic number of chromosomes

9. That fact prevents this from happening
Nothing =

10. That fact allows this to happen+
Pug
Beagle

11. That fact allows this to happen=
Puggle

12. That fact allows this to happen
Mule = male donkey and a female horse

13. That fact allows this to happen
Liger Tigon

14. Chromosomes (cont) Types 1) Autosomes 2) Sex Chromosomes - female = XX
male = XY

15. The sex of some species is determined by the temperature of the environment during incubation
(mostly occurs in reptiles)

16. Chromosomes (cont) Humans have 46 chromosomes (23 pairs)
- 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair)
- a diploid # (2n) of 46 and a haploid # (1n) of 23

17. Karyotype = picture of an individual’s chromosomes

18. Homologous Chromosomes vs. Sister Chromatids
Homologous Chromosomes = two separate chromosomes, one from mom and one from dad
- very similar in size and carry the same genes, but they are not copies of one another

19. Homologous Chromosomes vs. Sister Chromatids (cont)
In contrast, each half of a duplicated chromosome is called a chromatid
- together, the two chromatids are called sister chromatids
- thus, sister chromatids refers to the duplicated chromosome that remain attached (by the centromere)

20. Homologous Chromosomes
Homologous chromosomes (shown duplicated) are two separate chromosomes – one inherited from the mother and one from the father
Sister Chromatids
Sister Chromatids

21. Homologous Chromosomes vs. Sister Chromatids (cont)
Homologous chromosomes split in Meiosis I
Sister chromatids split in Meiosis II

22. Meiosis
= a form of nuclear division that divides a diploid cell into a haploid cell
- makes egg and sperm
- 2 rounds of division (Meiosis I and Meiosis II)

23. Meiosis (cont) Meiosis I – divides homologous chromosomes
Meiosis II – divides sister chromatids
The overall process produces haploid cells.

24. Meiosis I

25. Meiosis II

26. Gametogenesis 1) spermatogenesis = sperm production (4 haploid cells)
- even distribution

27. Spermatogenesis

28. Gametogenesis (cont) 2) oogenesis = egg production (1 haploid cell)
- uneven distribution (polar bodies created)

29. Oogenesis

30. Comparing Mitosis and Meiosis
- Produces genetically identical cells
- Results in diploid cells
- Takes place throughout an organism’s life
- Involved in asexual reproduction
Meiosis
- Produces genetically unique cells
- Results in haploid cells
- Takes place only at certain time in life cycle
- Involved in sexual reproduction