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Meiosis - Chapter 10.1 and 11.3 Sexual Reproduction Sexual reproduction creates genetic variability. That is why we all look different and you look different from your siblings! Define the following words… • Meiosis: – Sexual reproduction-production of gametes • Gamete: – Sex Cells (egg = females & sperm = males) – contain half the number of chromosomes (23) • Somatic Cells: – Body Cells – Contain 46 chromsomes • Haploid: – Half the chromosome number (n) – 1 of each pair of chromosomes (23) – Gametes are haploid • Diploid: – 2 of each type of chromosome (2n) – Somatic cells are diploid • Fertilization: – Sperm enters egg • Zygote: – Fertilized egg (diploid) How many chromosomes do we have in our cells? ▪ Human body cells have 46 chromosomes ▪ Each parent contributes 23 chromosomes ▪ Homologous chromosomes - a pair of chromosomes that have the same genes Homologous Chromosomes ▪ Carry the same genes that control the same inherited traits ▪ Alleles are the variations of one gene –Ex: eye colors can brown, blue, green, hazel, etc…. ▪ You inherit one chromosome from each parent! DNA Replication any cell divides, All DNA must be replicated Unduplicated homologous chromosomes Duplicated homologous chromosomes Meiosis • The sexual life cycle in animals involves meiosis • Meiosis produces gametes (23 chromosomes). • When gametes combine in fertilization, that creates a zygote. • A zygote has 46 chromosomes Meiosis • 2 Divisions Meiosis I - separation of homologous chromosomes Meiosis II - separation of sister chromatids DO NOW Label the following structures: Do Now What are ways that increase genetic diversity during meiosis? Meiosis 1 1. Crossing over occurs 1. Homologous chromosomes separate, randomly! 46 Duplicated 23 duplicated Crossing over = the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring. Crossing over • The same genes “switch”, which allows for unique gametes to form, different from the exact chromosomes given from the mother and father. • Occurs during Meiosis 1, Prophase 1 Meiosis 2 1. Sister chromatids separate into 4 different gametes, randomly. Each gamete has a unique combination of genes! 23 duplicated 23 unduplicated chromosomes in each gamete What creates genetic variability? 1. Crossing over - switching of genes during meiosis 1 creates a unique combination of genes 1. Independent Assortment - chromosomes separate into gametes randomly during meiosis 1 and meiosis 2 1. Random Fertilization - random sperm and egg combine to make a unique gamete •http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html# Meiosis 1 & 2 - Oogenesis (Eggs) and Spermatogenesis (Sperm)