Meiosis introduction CSCOPE Unit 08 Lesson 02 All graphics within this PPT are from Wikimedia Commons, unless otherwise noted.

Chromosomes What is a chromosome? How many chromosomes do A piece of coiled DNA How many chromosomes do human cells have? 46 (in non-sex cells) Do ALL humans have the same number of chromosomes in their cells? YES! (Except people with genetic disorders causing extra chromosomes or missing chromosomes) Where did the 46 chromosomes come from?

Turn to a friend and discuss… If we get our chromosomes from our parent, why do we not have a total of 92 (46 from mom and 46 from dad)? How does each parent manage to only give 23 chromosomes to their child? Allow students to think about and discuss these questions. Ask for responses from the class before moving to the next slide.

So… YOU were made from one cell from your mom and one cell from your dad. So, how is it the same? Shouldn’t you have double the number of chromosomes? No, the number is the same, because the egg and sperm cells only have half the number of chromosomes, so when they combine they have the full 46. SO, sex cells have how many chromosomes? 23 chromosomes **Point out to students that 46 chromosomes in a cell = a diploid cell, while 23 chromosomes in a cell = haploid cell.

Sex Cells -- gametes How are gametes (sex cells) formed, if they only have 23 chromosomes? Through a process called MEIOSIS Meiosis is similar to Mitosis but has some differences.

Mitosis — quick review Four Phases: DNA replication happens before Prophase Metaphase Anaphase (and) Telophase DNA replication happens before mitosis during the synthesis phase of the cell cycle.

Mitosis — quick review Discuss with students the four phases of Mitosis. Prophase: Chromosomes coil and become visible, nuclear membrane dissolves, spindle fibers form Metaphase: Chromosomes line up at the equator (discuss the centromere of the chromosome, where the identical chromatids are attached) Anaphase: Sister chromatids break apart and are pulled to opposite poles Telophase: Nuclear membrane reforms, chromosomes uncoil, ready for cytokinesis (complete division into two new IDENTICAL daughter cells)

Meiosis Meiosis Animation #1 Preview Meiosis Video Clips, or conduct a Google search for an animation of your choosing prior to class.

Mitosis vs. meiosis—primary difference Mitosis results in… Two IDENTICAL daughter cells—no genetic diversity Meiosis results in… FOUR daughter cells—that are different from parent cells, resulting in genetic diversity