1. Chapter 11
11-4 Meiosis

2. Intro Genes are located on the chromosomes in the cell nucleus.
2 things that Mendel’s principles of genetics required in order to be true:
Each org must inherit a single copy of every gene from both parents.
When an org produces its own gametes, those 2 sets of genes must be separated from each other.

3. Chromosome Number What does all this mean? Fruit fly-8 chromosomes.
4 from mom; 4 from dad.
The 2 sets are called homologous chromosomes (each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent).

5. Chromosome Number
A cell that contains both sets of homologous chromosomes is called diploid (2 sets).
Diploid is represented by the symbol 2N.
Fruit fly=diploid number of 8, or 2N=8.
Diploid cells contain 2 complete set of chromosomes and 2 complete sets of genes.

6. Phases of Meiosis
How are haploid (N) gamete cells produced from diploid (2N) cells?
That is where meiosis comes in.
Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

7. Phases of Meiosis Meiosis involves 2 divisions:
Meiosis II
By the end of meiosis II, the diploid cell that entered meiosis, has become 4 haploid cells.
Before meiosis begins, each chromosome is replicated.

8. Chromosome Number
Gametes of sexually reproducing organisms contain only a single set of chromosomes and a single set of genes.
These cells are haploid (1 set).
Fruit fly has a haploid number of 4, or N=4.

9. Meiosis I
In prophase I, there are 4 chromatids in a tetrad. Here they exchange portions of their chromatids in a process called crossing over. This results in an exchange of alleles between homologous chromosomes and produces new combos of alleles. The two new cells produced have sets of chromosomes and alleles different from each other and from the diploid cell that entered meiosis. The original two sets have been shuffled and sorted like a deck of cards!

10. Crossing Over

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

12. Gamete Formation
In male animals, the haploid gametes= sperm. In female animals, the haploid gametes=egg.
In females, generally only 1 of the cells produced by meiosis is involved in reproduction.

14. Comparing Mitosis & Meiosis
What is the difference between mitosis and meiosis?
Mitosis results in the production of 2 genetically identical diploid cells.
Meiosis produces 4 genetically different haploid cells.

15. Comparing Mitosis & Meiosis