1. DO NOW – 2/15/08 Complete the two Dihybrid crosses on eye color and widow’s peak. Report the phenotypic ratios in your DO NOW.

2. The Cell and Inheritance

3. How are genes passed? –An EGG is the female sex cell –SPERM is the male sex cell These are GAMETES: a mature sexual reproductive cell What is a somatic cell?

4. What is different about our cells? Somatic cells of humans have 46 chromosomes. Human sex cells have 23 chromosomes. –The sex cells have exactly half the number of chromosomes found in body cells.

5. When a sperm cell joined with an egg cell, the fertilized egg that forms has 46 chromosomes. The 46 chromosomes are in 23 pairs. Each pair has 1 chromosome from the mother and 1 chromosome from the father.

6. MEIOSIS MEIOSIS is the process by which the number of chromosomes is reduced by half to form gametes. The new gametes that are formed have half as many chromosomes as the somatic cells.

7. What do we like to do?…REVIEW!! The somatic cells of dogs have 78 chromosomes. - How many chromosomes do their gametes have? 39 The sex cells of silk worms have 28 chromosomes. –How many chromosomes do their body cells have? 56