Section 6 6 Genetic Variation On notebook paper

Section 6 -6 “Genetic Variation”

On notebook paper Title : Notes 6. 6 Genetic Variation 3 Main Ways During Meiosis (why ? ) Fertilization: (why? ) Crossing Over Draw Picture Page 190

6. 6 Meiosis and Genetic Variation KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity

6. 6 Meiosis and Genetic Variation • Sexual reproduction creates a unique combination of genes – independent assortment of chromosomes in meiosis – random fertilization of gametes

6. 6 Meiosis and Genetic Variation Crossing over during meiosis increases genetic diversity • Crossing over is the exchange of chromosome segments (pieces) between homologous chromosomes – this results in new combinations of genes – occurs during prophase I of meiosis I

6. 6 Meiosis and Genetic Variation

6. 6 Meiosis and Genetic Variation Crossing Over: Before Cross over After Cross over Homologous Chromosomes

6. 6 Meiosis and Genetic Variation • In mitosis, offspring are identical to the “parent” cell • In meiosis, chromosomes and the genetic information they carry are shuffled resulting in genetic variation

6. 6 Meiosis and Genetic Variation • 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

6. 6 Meiosis and Genetic Variation • Mutations: Spontaneous changes in DNA • These can result in good changes or bad changes in the traits –We’ll learn more about mutations when we talk about DNA.

6. 6 Meiosis and Genetic Variation Are You Unique? • Human body cells have 46 chromosomes, and sex cells have 23 • The number of different kinds of sperm or eggs that can be produced is 223 • When an egg and sperm unite you get 223 x 223. That’s over 70 trillion different zygotes that could be formed during sexual reproduction in humans

6. 6 Meiosis and Genetic Variation