1. 1 Review Write a summary of each phase of meiosis Use Analogies Compare the chromosomes of a diploid cell to a collection of shoes in a closet. How are they similar. What would make the shoe collection comparable to the chromosomes of a haploid cell 2 Review What are the principle differences between mitosis and meiosis 3 Review How does the principle of independent assortment apply to chromosomes Infer If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are

2. Ch 11 Introduction to Genetics
11.4 Meiosis

3. Diploid Cells Two sets of homologous chromosomes Somatic cells
One chromosome 2 from mom and one chromosome 2 from dad
Somatic cells
All cells other than sex cells
“2n”.

4. Haploid Cells
Only one set of chromosomes
Gametes
“n”.

5. Meiosis Similar in process to Mitosis Forms gametes Goes from 2n to n
Fertilization goes from n to 2n
Meiosis I
Meiosis II
Create FOUR haploid cells from ONE diploid cell.

6. Meiosis Phases Interphase Prophase 1 Metaphase 1 Anaphase 1
Telophase 1
Cytokinesis
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokinesis.

7. Chromosomes
Each chromosome consists of two copies ensuring that each new cell will have the same genetic information
The identical strands of DNA are each called chromatids and are held together by a centromere.

8. Interphase 1
Chromosome replicate.

9. Prophase 1 DNA coils up into Chromosomes Nuclear membrane breaks down
Chromosomes pair up into Tetrads
Tetrad
Homologous pair.

10. Prophase 1 Crossing over may occur
Chromatids of the homologous chromosomes cross over one another
Crossed sections of the chromatids are exchanged.

12. Metaphase 1
Homologous Pairs Line up down center of cell.

13. Anaphase 1
Chromosome Pairs separate
Pulled to opposite poles of cell.

14. Telophase 1 and Cytokinesis
Nuclear membrane forms around each cluster of chromosomes
Cytokinesis occurs forming two cells.

15. Now have two daughter cells that are genetically different
Now are Haploid.

16. Prophase 2 Chromosomes become visible Nuclear membrane breaks down
No additional crossing over.

17. Metaphse 2
Chromosomes line up in the center of each cell.

18. Anaphase 2
The paired chromatids separate.

19. Telophase 2 and Cytokinesis
Chromosomes arrive at poles
Nuclear envelope reforms
Cytokinesis occurs forming four cells.

20. Sperm Ova or Ovum (egg) Fertilization Zygote Male Gamete Female Gamete
When the two gametes combine
Zygote
Fertilized egg.

21. Mitosis vs. Meiosis Creates 4 daughter cells Creates 2 daughter cells
Genetically different from parent cell
Haploid (n)
2 divisions
Produces gametes
Crossing over
Genetic Variations.
Creates 2 daughter cells
Cell is identical to parent
Diploid (2n)
1 division
Produces ‘body cells’ (somatic cells)

22. You are “One in a Million”
Over 8 million possible gamete combinations from dad
Over 8 million possible gamete combinations from mom.

23. You are actually “One in 64 TRILLION”

24. Gene Linkage
The closer two genes are located on a chromosome the more likely those alleles will occur together
Less of a chance for crossing over to occur in between
Used to map out location of genes.

25. Gene Map

26. Haploid and diploid numbers are designated N and 2N
Haploid and diploid numbers are designated N and 2N. The table shows haploid or diploid numbers of a variety of organisms.
Copy the table and complete it and then use it to answer the questions on the next slide.

27. Calculate What are the haploid numbers for the fern and onion plants
Interpret Data In the table, which organisms diploid number is closest to a human
Apply Concepts Why is a diploid number always even
Evaluate Which organism’s haploid and diploid numbers do you find most surprising- why