1. KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

2. Students will be able to:
Objectives:
Students will be able to:
*describe how sexual reproduction creates unique gene combinations
*explain how crossing over during meiosis creates genetic diversity.

3. Sexual reproduction creates unique combinations of genes.
Sexual reproduction creates unique combination of genes.
independent assortment of chromosomes in meiosis=223
random fertilization of gametes 223x223 =64 trillion
Unique phenotypes may give a reproductive advantage to some organisms.

4. Crossing over during meiosis increases genetic diversity.
Crossing over is the exchange of chromosome segments between homologous chromosomes.
occurs during prophase I of meiosis I
results in new combinations of genes

5. Chromosomes contain many genes.
The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.
Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.
Genetic linkage allows the distance between two genes to be calculated.

6. Review
Describe how sexual reproduction creates unique gene combinations.
Explain how crossing over during meiosis creates genetic diversity
Fruit fly gametes each have four chromosomes, representing 2^4, or 16, possible chromosome combinations. How many chromosome combinations could result from fertilization between a fruit fly egg and a sperm cell?
Suppose two genes are very close together on a chromosome. Are the genes likely to be separated by crossing over? Explain
You know that you get half your DNA from your mom and half from your dad. Does this mean you got one-quarter of your DNA from each of your grandparents? Explain
Mitosis creates daughter cells that are genetically identical to the parent cell. If crossing over occurred between sister chromatids during mitosis, would it increase genetic diversity?