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.

The Cell and Inheritance

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?

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.

• 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.

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.

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