1. Meiosis (necessary for sexual reproduction)
Reduction Division  sex cells  egg/sperm (germ cells)
2N diploid  N haploid ???why??
Humans chromosomes  23 chromosomes
Sexual Reproduction (N) gametes combine
2N diploid # restored)
↑ Diversity (combine 2 sets of genes)
 ?effects on evolution
Shuffling during synapsis
Xing over of homologous prs in Prophase 1
Draw egg (N) + sperm (N) cell  fertilization
2N diploid # restored

2. Meiosis
# of chromosomes is cut in 1/2 thru separation of homologous chromosomes in a diploid 2N cell
2N diploid cell contains 2 complete sets of chromosomes
(1 set of chromosomes/genes from each parent)
Mendel: All of an organisms cells except gametes contain 2 alleles for a trait
Sex cells undergo meiosis to produce
Gametes (ovum/egg and sperm)
Symbols ________ ________

3. Somatic/Body cells 46 chromosomes (23prs)
22 prs/44 autosomes –not sex chromosomes (#’s1-22)
1 pr/2 sex chromosomes (#23)
Homologous Chromosomes: Corresponding chromosomes
between male + female
Homologs: chromosomes themselves
Cell that contains both sets of homologous chromosomes
(from each parent) = 2N diplod
2N diploid cells contain 2 complete sets of genes-
1 from each parent
Gametes/Sex cells contain only a single copy (1 set) of genes b/c alleles (forms of a gene) are separated during gamete formation (oognesis _____ and spermatogenesis ________)

4. Meiosis: produces 4 haploid cells (N) Genetically different from
each other & original
Stages of Meiosis
Meiosis I
Interphase 1: Chromosomes replicate (S Phase)
Growth & development (G1 phase)
Organelle synthesis (G2 phase)
Chromosomes condense & coil
Centrioles replicate

5. Prophase 1: Chromosomes visible
Each chromosome seeks its homologous pr to form
tetrad in synapsis (maternal + paternal)
Shuffling: way/side homologous pr ends up on  CHANCE!
Xing over: between homologus prs exchange of genetic info on
chromatids
 new combos of genes
Centrioles migrate & spindles form
Homologous prs migrate to spindle fibers
Nuclear membrane breaks ↓
Shuffling demo- line students up on opposite sides
Include Xing over using appendages

6. Metaphase 1: Spindle fibers attached to chromosomes –
at kinetocore
Tetrads (homologous prs) line up on equator
**Chance which side maternal/paternal pr ends up on
(w/ rest of genes on chromosomes on that side)

7. Anaphase 1: Dysjunction
Homologous chromosomes (each w/ 2 chromatids) move to
opposite poles along spindle fibers
Nondysjunction: homologous pr(s) fail to separate
 gametes w/ too many/few chromosomes
Ex. Trisomy 21 Down Syndrome
Kleinfleter’s 47XXY
Turner’s 45XO
Jacob’s 47XYY
Polyploidy: nondysjunction of entire set of
chromosomes  3N, 4N, etc
Fatal in animals 
Can be  in plants  hearty,
disease resistant, big!

8. Telophase 1: Followed by cytokinesis (division of cytoplasm)
Chromosomes gather in nuclei
Nuclear membrane reforms
Cells contain a single set of chromosomes/genes (N-haploid)
2, haploid, (N) Daughter cells

9. Meiosis II (like mitosis- w/ no DNA replication)
Interphase II: No DNA Replication
Synthesis of organelles
Chromatin mesh

10. Prophase II: Chromosomes condense, coil  visible
Centrioles migrate & spindles form
Chromosomes migrate to spindles attach at kinetocore

11. Metaphase II: Chromosomes line up on equator

12. Anaphase II: Sister chromatids separate & move towards opposite poles
along spindle (Nondysjunction can occur here also)
** b/c of shuffling & Xing over in Prophase I each cell has a different genetic makeup- combo of genes in each gamete  Random
**chromosomes carry genes & genes carry alleles (forms of a gene) for specific trait (chromosome carry genes for specific traits  DNA)

13. Comparative Scale of a Gene Map
Section 11-5
Mapping of Earth’s Features
Mapping of Cells, Chromosomes, and Genes
Cell
Earth
Country
Chromosome
Chromosome fragment
State
Gene
City
People
Nucleotide base pairs

14. Telophase II: followed by Cytokinesis
Chromosomes gather & Nuclear membrane reforms
Produces 4 haploid (N) gametes/sex cells for
sexual reproduction

16. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

17. How does Xing over affect inheritance?
It changes the combo of alleles on the chromosomes
Ex. fruit fly w/ red eyes & brown body or white eyes & yellow body
Xing over  red eyes w/ yellow body and white eyes w/ brown body
Xing over used to map genes closer 2 genes are located on a chromosome the Less likey they’ll be separated by xing over
By observing how frequently Xing over separates any 2 genes  helps
determine genes relative position on chromosome

19. Mitosis vs Meiosis

20. Mitosis vs Meiosis
2 identical daughter cells
4 genetically different cells
2N diploid 2N diploid
2N diploid  N haploid
Asexual
Sexual
1 division
2 divisions
Body/Somatic cells
Sex Cells
Growth Development Repair
Produce gametes (egg/ovum & sperm)
Less genetic diversity
↑ genetic diversity (genes from 2 parents combine, Prophase 1 shuffling (in synapsis), Xing over
Occurs after fertilization/ formation of Zygote  growth & differentiation
Occurs at puberty

21. Gametogenesis: formation of gametes 2N diploid N haploid
Spermatogenesis  Sperm Formation
Oogenesis  Egg (ovum) Formation

22. Spermatogenesis: males, in the testes
produces 4 viable sperm cells (small)

23. Oogenesis: females in the ovaries
(follicle in ovary is where mature egg develops)
produces 1 egg/ovum (lgst cell in body) + 2 or 3 polar bodies
≠ division of cytoplasm  ovum gets all the nutrients (why)?
Travels thru fallopian tube (propeled by cilia) for fertilization by sperm

24. Spermatogenesis vs Oogenesis

25. Spermatogenesis vs Oogenesis
Males
Females
4 viable haploid sperm cells
1 viable haploid egg/ovum + 2 or 3 polar bodies
Small
Largest cell in human body
Motile
Non motile
Produced in testes
Produced in ovaries (*follicle)
Produce millions at a time
Produce 1/month
= division of cytoplasm
≠ division of cytoplasm
Occurs at Puberty

26. Karyotype: Chromosome map
Cells must be undergoing mitosis for chromosomes to be visible.
Count chromosome prs, look for abnormalities
Ex. Nondysjunction, Translocation, Inversion of chromosomes
Normal male

27. Normal female