1. Cell Division - Meiosis

2. I. Who Does Meiosis and Why?
A. Who: All Multicellular Eukaryotes
Animals, Plants, Fungi, some algae
B. Why: Meiosis is needed for sexual reproduction
C. Why do Sexual Reproduction ?
1. It allows genetic recombination
2.New combinations of genes may ..
a. better suit environments
b. allow offspring to survive radical
environmental change
c. allow offspring to survive a disease
outbreak

3. II. Vocab
A. Cells produced by meiosis =
Gametes
B. Sex Chromosomes = determine sex
(in humans XX = female, Xy = male)
C. Autosomes = any chromosome not
used to determine sex of offspring

4. .
D. Gametes = haploid cells made by
meiosis
E. Haploid cells have 1 set of
chromosomes….. (1 of each kind)
1. called 1n cells
2. mathematical representation
3. n = number of different C types

5. Example: Humans have 23 different types
22 autosomes +
1 sex determining
Gametes would have 1 of each kind
So the 1n number for humans is… 23
(1*n) = (1*23)

6. .
F. Diploid cells have 2 of each kind of chromosome
G. 2n cells are diploid cells
Example:
Humans = 23 types
Diploid cells have
2 of each type ->
2n Chromosome
number = 46
(2*23)= (2*n)

7. Based on the Cat Karyotype below, calculate the 1n and 2n number for cats
18 different autosomes (C # 1-18) one pair of sex chromosomes
So 19 different kinds
1n = 1(19) = 19
2n = 2(19) = 38

8. III. How/Where Haploid Cells are produced
A. Where: Animals: Meiosis only in gonads
1. Gonads = reproductive organs
a. testis b. ovary
2. Specialized cells in gonad do meiosis
a. spermatocytes b. oocytes
3. Spermatocytes and oocytes are constantly replaced by specialized Spermatogonia cells & oogonia cells

10. IV. Spermatogenesis
A. Spermatogonia cells do Mitosis make
1. a 1◦ spermatocyte
2. a cell that stays a spermatogonia
B. The 1◦ spermatocyte does meiosis to make 4 spermatids

11. C. Spermatids differentiate into sperm
1. Acrosome = vesicle
w/ penetrating enzymes
2. Nucleus = 1n
3. Midpiece makes ATP
& powers flagellum
4. Tail = flagellum

12. V. Oogenesis
Oogonia do
Mitosis to make
1 primary Oocyte
Which does…
Meiosis I to make
1 secondary oocyte and one polar body
Meiosis II makes
1 ovum &1 polar body

13. Meiosis I:separate homologous pairs (cells become 1n with X shape C)
Prophase I :
same as mitosis +
Synapsis &
crossing over
Metaphase I :
C line up in pairs

14. .
Anaphase I :
Homologs move to
opposite poles
(cohesin along arms breaks down)
(cohesin at centromeres remains)

15. Telophase I :
Cytokinesis simultaneously
X shaped C reach poles
Many cells do not decondense C or
reform nuclear E
Spindle only partly broken down

16. Homologous Chromosomes
Homologous Chromosomes are
same C type
same length
code for same genes
(but can be different versions)
Unless they are X and y which are the only pair of Homologues that do not look alike

17. Synapsis
Homologous Chromosomes pair up
Line up gene to gene then physically connect along their arms
Proteins form a synaptonemal complex that bind them together

18. .
Crossing Over : Non-sister chromosomes trade corresponding segments of DNA
Genes far from centromere cross over most often
Location of a gene on a chromosome =
the gene’s locus (loci)
Distance from centromere measured in
map units

19. Chiasmata
X shaped region where crossing over has happened.
Synaptonemal complex has broken down but …
Cohesions still hold sister chromatids together

21. Meiosis in Fungi
Fungal bodies formed of hyphae
Filaments made of chains of 1n cells
Hyphae interweave to form fungus body
The body mass is called a mycelium

23. Phylum Ascomycota don’t make mushrooms
Hypha can be + or –
If one of each meet then…
2 cells (one + one-) fuse cytoplasm
(plasmogamy)
Then fuse their nuclei … now 2n
(karyogamy)
Then do meiosis…making 4 haploid nuclei

24. Each 1n nucleus does mitosis
So now 8 nuclei in the cell
Each nucleus grows a tough casing around it and becomes a
Spore (ascospore)
Spores disperse on wind
Germinate to make new 1n hyphae .

26. The ascospores that form from one cell stay together in a capsule called an ascus

27. Perithecia = ascocarp

28. Homologous C both have gene for spore color…one tan color one black color
No crossing over
= 4:4
Any other pattern results from crossing over

29. Genetic Variation
Increased by crossing over
Increased by Independent Assortment..
Each pair of homologues lines up randomly and Independent of how other pairs line up
# different gametes formed = 2n
Humans =
223 or 8,399,608