Meiosis Catalyst: What type of cells does mitosis occur in? Somatic cells are 2N. What does this mean? Why is it important that cells copy all their DNA during mitosis, and become 4N? Write in complete sentences! Don’t talk during the Catalyst!

Agenda Catalyst Catalyst Review Meiosis BRAIN GAIN Comparing meiosis to mitosis EQ HOMEWORK: Finish Mitosis vs. Meiosis sheet Study for Cellular Processes unit test tomorrow! (ATP, Photosynthesis, Cellular Respiration, Mitosis, Meiosis)

Meiosis Review What type of cells does mitosis occur in? Mitosis occurs in somatic cells. Somatic cells are 2N. What does this mean? 2N means there are two of each type of chromosome. Why is it important that cells copy all their DNA during mitosis, and become 4N? It is important that cells copy all their DNA during mitosis and become 4N because the cell splits in half. When the parent cell splits in half, the daughter cells will still have 2N, an exact copy of the parent cell. 3

By the end of today, SWBAT… State the purpose of meiosis Objectives By the end of today, SWBAT… State the purpose of meiosis Compare mitosis and meiosis

Review of Mitosis Somatic cells have 2 of each type of chromosome Mitosis produces cells that are 2N. 2N→4N 2N 2N

Review of Mitosis Point out that what is going on here: the chromosomes are doing a dance, but the DNA had doubled and now they split evenly between the two cell.

But wait… There’s another type of cell division for one specific purpose!

Meiosis is for sexual reproduction Key Point #1: Meiosis is cell division for gametes. Gametes = sex cells Eggs for women, Sperm for men Meiosis is for sexual reproduction

New Vocabulary Somatic cells have 2 of each type of chromosome (2N). This means that somatic cells have all the instructions necessary to make an organism. Another word for 2N is diploid. Somatic cells are diploid. Gametes only have 1 of each type of chromosome (1N). This means that they only have HALF of the DNA necessary to make an organism. Another word for 1N is haploid. Gametes are haploid.

Now does it make sense why you need one sperm and one egg??

Why? 2N 4N Key Point #2: Gametes must be haploid (1N) Every human must have two copies of each chromosome If gametes were diploid (2N), the child would not survive 2N is the regular number of chromosomes! You don’t want a baby with 4N!!!!!! 2N 1N How do we get haploid cells? Well, in meiosis… cells divide TWICE! 2N 4N 2N 1N

So how does this work? In meiosis, there are two rounds of cell division 2N→4N MEIOSIS I MEIOSIS II 1N 2N 1N 1N The starting 2N cell is a germ cell; it produces gametes. Germ cells are the only cells in the body that undergo both mitosis (to create more germ cells) and meiosis (to create gametes). 2N 1N

So how does this work? MEIOSIS I MEIOSIS II 2N 4N 2N 2N 1N 1N 1N 1N In meiosis, there are two rounds of cell division 2N 4N MEIOSIS I 2N 2N The starting 2N cell is a germ cell; it produces gametes. Germ cells are the only cells in the body that undergo both mitosis (to create more germ cells) and meiosis (to create gametes). MEIOSIS II 1N 1N 1N 1N 13

Family Matters Meiosis can explain a lot of things in life… Why am so much better looking than my brother, even though we have the same parents? So if gametes need to be haploid, not diploid, then they can’t divide via mitosis. They have to divide through meiosis.

Thank you, meiosis!

NOT IDENTICAL Key Point #3: Meiosis produces genetically DIFFERENT cells. Why different? Genetic information between chromosomes gets switched. Analogous parts of the chromosomes get switched. So the reason my sister and I look different is she came from eggs/sperm that are DIFFERENT than the ones I came from. Germ Cell

More Meiosis

A Closer Look 2N 1N 1N 1N 1N Use this page to show them that the original 2N cell has twice as much DNA as each of the 4 products of meiosis.

Hold Up Check Our Understanding…. What is mitosis is for? What is meiosis is for? What’s the difference between haploid and diploid? Why is it important that gametes are haploid? Student voices!!!

Meiosis produces… Identical cells Different cells 23 types of cells Guided Practice Meiosis produces… Identical cells Different cells 23 types of cells Two copies of each cell

Meiosis occurs in… Somatic cells Gametes Chromosomes Guided Practice Meiosis occurs in… Somatic cells Gametes Chromosomes All eukyarotic cells

How many times do cells divide in meiosis? 1 2 3 4 Guided Practice How many times do cells divide in meiosis? 1 2 3 4

Guided Practice The cells produced by meiosis are _____, also known as ______. Haploid… 1N Diploid… 1N Haploid… 2N Diploid… 2N

Guided Practice Gametes have _____ copy/copies of each type of chromosome. 1 2 23 46

Guided Practice What would happen if gametes were 2N? Children would be 2N, and die Children would be 4N, and have superpowers Children would be 4N, and die Trick question, gametes are 2N!

Were You Paying Attention? I’m going to ask the same questions again! Answers are scrambled…

Meiosis produces… Different cells Two copies of each cell Guided Practice Meiosis produces… Different cells Two copies of each cell Identical cells 23 types of cells

Meiosis occurs in… Chromosomes Somatic cells All eukyarotic cells Guided Practice Meiosis occurs in… Chromosomes Somatic cells All eukyarotic cells Gametes

How many times do cells divide in meiosis? 4 3 2 1 Guided Practice How many times do cells divide in meiosis? 4 3 2 1

Guided Practice The cells produced by meiosis are _____, also known as ______. Haploid… 1N Haploid… 2N Diploid… 1N Diploid… 2N

Guided Practice Gametes have _____ copy/copies of each type of chromosome. 2 46 23 1

Guided Practice What would happen if gametes were 2N? Children would be 4N, and die Children would be 4N, and have superpowers Trick question, gametes are 2N! Children would be 2N, and die

So far, we’ve only been talking about meiosis Step Yo’ Game Up! So far, we’ve only been talking about meiosis But we need to be able to COMPARE meiosis and mitosis

Put in your notes….YOU TRY 2 MINS MITOSIS MEIOSIS SOMATIC OR GAMETES? HAPLOID OR DIPLOID? 2N OR 1N? IDENTICAL CELLS OR DIFFERENT CELLS? 1 OR 2 DIVISIONS?

IDENTICAL CELLS OR DIFFERENT CELLS? ANSWERS MITOSIS MEIOSIS SOMATIC OR GAMETES? somatic gametes HAPLOID OR DIPLOID? diploid haploid 2N OR 1N? 2N 1N IDENTICAL CELLS OR DIFFERENT CELLS? identical different 1 OR 2 DIVISIONS? 1 division 2 divisions

Produces cells with 2N chromosomes Guided Practice Produces cells with 2N chromosomes Mitosis Meiosis

Guided Practice Creates diploid cells Mitosis Meiosis

Produces four DIFFERENT daughter cells Guided Practice Produces four DIFFERENT daughter cells Mitosis Meiosis

Creates cells with 1N chromosomes Guided Practice Creates cells with 1N chromosomes Mitosis Meiosis

Genetic information between chromosomes gets switched Guided Practice Genetic information between chromosomes gets switched Mitosis Meiosis

Guided Practice Which of the following is true? There are more cell divisions in mitosis than meiosis There are more cell divisions in meiosis than mitosis There are the same number of cell divisions in both The cell does not divide in mitosis or meiosis 1 in mitosis, 2 in meiosis

Guided Practice Mitosis occurs in _____, meiosis occurs in _____ Animals… Animals and plants Gametes… somatic cells Eukaryotic cells… prokaryotic cells Somatic cells… gametes

Guided Practice Mitosis produces _____ cells, meiosis produces _____ cells. Haploid… diploid Gametes… somatic Eukaryotic… prokaryotic 1N… 2N

Work it out. Meiosis section. We have LIMITED TIME. Use your time WISELY. Mitosis vs. Meiosis worksheet (Last page of your packet) If you are having trouble, NOW is the time to get help. We have a UNIT TEST tomorrow.

Exit Questions What is the purpose of meiosis? How many cells does meiosis produce? Use your knowledge of meiosis to explain why Ms. S so much better looking than her brother. (Hint: it has to do with sperm and egg cells.) Write in complete sentences! Don’t talk during the Catalyst!

The following slides are extension Will not be tested; only if students are curious

Women only produce one viable egg in meiosis, the other three cells are polar bodies that will be destroyed. Women only produce a few hundred eggs over the course of their entire lives. extension Oogenesis

Men are busy – meiosis produces roughly 250,000,000 sperm per day!!! extension Spermatogenesis