1. IV. Meiosis A. Chromosome number 1. Every individual has two sets of chromosomes. One from the mother one from the father. When the chromosomes pair up for the same trait they are called homologous chromosomes.

2. 2. A cell that contains homologous chromosomes (2 genes) is said to be diploid/ 2n. 3. Gametes (egg /sperm) have only one chromosome and are said to be haploid/ n.

4. B. Phases of Meiosis 1. 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. 2. Meiosis I- ****The homologous chromosomes line up BUT then they CROSS OVER, exchanging genetic information.

6. 3. Meiosis II- The two cells produced by meiosis I now enter a second meiotic division. The final product = start with 1 cell with 46 chromosomes and get 4 DIFFERENT cells each with 23 chromosomes. Go to Internet: www.SciLinks.org code cbn-4114 to view meiosis.

7. V. Linkage and Gene Maps A. Gene linkage 1. Thomas Hunt Morgan research on fruit flies led him to the principal of linkage. 2. Morgan discovered that many genes appeared “linked” together.

9. 3. It is the chromosomes, however, that assort independently not individual genes. 4. Mendel DID miss gene linkage.

10. Even though if two genes are found on the same chromosome this does not mean they are linked forever. Crossing over can occur. 6. Crossing over creates genetic diversity.

11. 7. A gene map shows the relative location of each gene. See page 280 figure 11.9