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

KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity

Sexual reproduction creates a unique combination of genes independent assortment of chromosomes in meiosis random fertilization of gametes

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

Homologous Chromosomes Crossing Over: Before Cross over After Cross over Homologous Chromosomes

In mitosis, offspring are identical to the “parent” cell 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

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

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.

Human body cells have 46 chromosomes, and sex cells have 23 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