Do Now 2.7 (Week 23) Objectives: Be able to define fertilization and zygote. Describe how chromosome number changes during sexual reproduction. Identify the evolutionary advantage of sexual reproduction over asexual. Task: If an organism is 2n=4, how many different combinations of chromosomes are possible in its n=2 gametes?

Fertilization: n + n = 2n Fertilization is the process of haploid gametes combining to form a diploid cell, called a zygote. Zygote: a fertilized egg cell able to develop into a new individual

It all Starts With Meiosis Human meiosis: 2n = 46  n = 23 How many different combinations of chromosomes can meiosis produce in humans? Without any mutations, what is the total number of genetically distinct offspring two individual parents can produce?

Meiosis & Fertilization Example 2n = 4 dad 1n = 2 sperm 2n = 4 zygote MEIOSIS MAKES GAMETES FERTILIZATION MAKES ZYGOTE 2n = 4 mom 1n = 2 egg In humans, any two parents can produce over 64,000,000,000,000 (64 trillion) combinations of chromosomes with meiosis and fertilization.

Why Sex? What is the biggest genetic advantage of sexual reproduction? To the fish video (PBS evolution library)

To the interwebs!