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Transcript
MEIOSIS Sexual Reproduction Somatic cells vs. Gametes Our bodies have 2 different types of cells ⬜ Somatic cells ◼ ◼ Component of body tissue. Example: ⬜ Gametes ◼ sexual reproduction. ◼ Example: ▫ sperm cell and egg cell. ▫ muscle, bone, skin, nerve, heart and brain. ◼ ◼ 46 chromosomes ▫ 23 pairs End product of Mitosis Sex cells; involved in ◼ 23 chromosomes ▫ (No pairs) ◼ End product of Meiosis ◼ Sperm + egg (fertilized) = zygote Gamete (23) + Gamete (23) = Zygote (46) HOW DO WE MAKE GAMETES? We need to produce cells with ½ the amount of chromosomes (23). We do that through Meiosis! ⬜ Draw these Homologous Chromosomes ◼ ◼ Label the chromosome from Dad and the chromosome from Mom Color the banded genes on each chromosome. ▫ These bands represent different versions of the same gene (trait) Why is genetic diversity a good thing? ⬜ Sexual Reproduction = Variety ⬜ Why? ◼ ◼ ⬜ ! Why don’t your siblings look EXACTLY like you? Why don’t you look EXACTLY like your parents? Let’s talk about 3 sources of Variety in Sexual Reproduction. 1. Crossing Over increases Variety • Occurs during Meiosis I • Homologous chromosomes form tetrads (they find their pair) in Prophase I. • While in tetrads, chromosomes exchange genetic material to make new combinations. (Recombination) 2. Independent Assortment increases Variety ⬜ Independent Assortment : Homologous pairs can line up in 2 ways: ⬜ Mom’s chromosome on left or Dad’s chromosome on left. ⬜ ⬜ ⬜ This produces different genetic combinations in the daughter cells. ⬜ In humans 223 = 8 million combinations! IS THIS ENOUGH Variety? 3. Random Fertilization increases Variety • Any sperm can fertilize any egg. • Dad has 8 million different genetic variations in sperm. • Mom has 8 million different genetic variations in eggs. • 8 million x 8 million = 64 trillion possible babies • Crossing over squares that number! 64 trillion squared = 27 zeros!! 4,000,000,000,000,000,000,000,000,000 Twins ⬜ What are fraternal twins? ◼ ⬜ Two fertilized eggs What are identical twins? ◼ A single zygote that splits in two or three or..