1. Like Mitosis, but half as good!
11-4 Meiosis
Like Mitosis, but half as good!
Interactive pgs

2. Genes Genes are located on chromosomes in the nucleus
1) Organisms must inherit a single copy of every gene from each of its “parents”
2) In gamete formation, two sets of genes must be separated from each other
Genes

3. Each organism has 2 sets of homologous chromosomes (1 set from each parent)
Fruit flies have 8 chromosomes (4 from each parent)
Diploid cells contain both sets (2N)
Ex: fruit flies have 2N=8
Haploid cells have only one set (N)
Gametes or sex cells
Ex: fruit flies have N=4
Chromosome Number

4. Homologous Chromosomes:
Paternal
Maternal
Homologous chromosomes
sister chromatids
Tetrad

5. Cell division in which the number of chromosomes in a cell is cut in half
(diploid  haploid)
Leads to the production of haploid gametes
Two stages:
Meiosis I
Meiosis II
Meiosis

6. Meiosis I Interphase I: chromosomes are duplicated
Prophase I: corresponding homologous chromosomes form a tetrad
Crossing over: chromosomes exchange portions of their chromatids
Leads to new combinations of alleles
During this stage, homologous chromosomes separate and 2 new haploid cells are formed
Meiosis I

7. Meiosis II NO replication of chromosomes
Chromatids separate and the 2 haploid cells divide to form 4 haploid daughter cells
Meiosis II

8. Use pgs. 276-277 to label the stages (a-j)
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase I & Cytokinesis
Telophase II & Cytokinesis
Prophase II
Metaphase II
Anaphase II
4 haploid cells

9. Crossing Over (during Prophase I)

10. Males: SPERMATOGENESIS results in 4 equal sized gametes called sperm
Females: OOGENESIS results in 1 large egg and 3 other nonuseful cells called polar bodies
Gamete Formation

12. Comparing Mitosis & Meiosis
Production of 2 genetically IDENTICAL diploid cells
Body cells
Meiosis
Production of 4 genetically DIFFERENT haploid cells
Makes gametes (sex cells)
Comparing Mitosis & Meiosis