3/20/ find your new seat- YOU CHOOSE – Sit by people YOU WORK WELL WITH – I reserve the right to move you – Do not move the stools! – If you are on the sides you will move to the front table when we split the table next class bell ringer/exit..whatevs 3- follow along lecture- take notes AND model cell division! 4- review worksheet- finish for HOMEWORK!

Cell Division (6.2) Intro Get it?

Types of Cell Division (Level I) Mitosis Growing new cells Cells make identical copies Meiosis Making reproductive cells Cells pass on only half the chromosomes

Overview MitosisMeiosis

APPROXIMATELY HOW MANY CELLS IS AN AVERAGE PERSON MADE OF?

A. You have approximately 100 trillion cells

HOW MANY CELLS DID YOU START OFF AS?

One SINGLE cell! SO, how did you come to be so many more cells?

Mitosis!! Single cell (zygote) approximately 100 trillion cells Mitosis

Purpose of Mitosis? Make identical copies of cells Make new tissue or repair tissue New cells are genetically identical Allows them to be coordinated Makes new cells to replace dead cells

Cell differences come from epigenome, not genome Mitosis + Specialization Meiosis

What About Reproduction? We only pass on half our chromosomes in gametes (sperm or eggs) Which half you pass on is determined randomly in meiosis Gametes. Notice they contain half the chromosomes Germ Cell

Meiosis differences 2 stages of cellular division = 4 daughter cells daughter cells contain half the original chromosomes (in humans 22 autosomes plus an X or Y for a total of 23) Daughter cells are unique

Interphase Most of the time…The cell doing it’s thing… IF ITS GOING TO DIVIDE… DNA must be copied Cell grows and copies organelles etc.

Vocabulary you need!!! TermDefinitionExampleIn Our Model ChromosomeSingle segment of DNA Sister Chromatids Identical copy of DNA Homologous Chromosomes Set of similar chromosomes from each parent E.g. we have 2 chromosome 1s that are homologous From mom From Dad Before Duplication After Duplication

Don’t Confuse Them… That Seems to Be the BIG Problem A B d e B a d E A B d e A B d e B a d E B a d E Identical, same alleles Similar, same genes, dif alleles

Human Genome Homologous Pair (before DNA Replication) Normally we have 22 homologous pairs of autosomal chromosomes + 2 Xs (female) or an X and a Y (male)

Modeling Mitosis and Meiosis (Level II) We begin with 3 pairs of homologous chromosomes (6 total) KEY Blue = plasma membrane White ring = Nucleus # of beads = chromosome # Red = from Dad Yellow = from Mom Homologous Chromosomes

Control of Mitosis and Meiosis Like the cell itself, do not proceed to the next step until you get the correct signal

MITOSIS Cell growth and repair ***Note, we will not be quizzing you on the names of each stage. But you should understand the overall process

Step 1 - Interphase Copy the DNA Sister Chromatids

Step 2 – Prophase (Nucleus Disappears) WHY?

Step 3 – Metaphase

Step 4 - Anaphase

Step 5 – Telophase (Nuclei Form)

Step 6 – Cytokinesis (Cells Divide)

Overall

Meiosis – Cell Starts the Same Way

Step 1 - Interphase Copy the DNA

Step 2 – Prophase I Homologs pair up – lots of possible ways

Step 2 – Prophase I Alternate pairing (challenge: how many combos are there?)

Step 3 – Metaphase I

Notice the Difference: MitosisMeiosis I

Step 4 – Anaphase I

Step 5 – Telophase I / Cytokinesis I

Step 6 – Prophase II

Step 7 – Metaphase/Anaphase II

Step 8 – Telophase II

Step 9 – Cytokinesis II

Overall

Mitosis Products vs. Meiosis Products

Notice: Not all of your gametes are the same Meiosis shuffles the genes, increasing the diversity of offspring

2 Gametes Come Together to Make a New Zygote Homologous

Human Lifecycle

Why Sexual Reproduction? DIVERSITY! Meiosis produces an incredible amount of diversity Diversity is good! B/C diversity increases chances that our species will survive

You Are LITERALLY 1 in a trillion Each parent had 23 pairs of chromosomes. For each chromosome there are 2 options they could have given you There are 2 23 possible chromosome combinations to make a gamete =8,388,608 possibilities for each sperm and egg So you are 1 out of 8,388,608 2 possibilities You are quite literally 1 in a trillion (1 of 70,368,744,200,000 possible combinations your parents could have had)

Why is this funny?

Rapid Review – Level I Mitosis Makes 2 identical cells Ensures all cells in the body are genetically identical Growth, repair of tissues etc. Makes all cells in the body except sperm and egg (and original zygote cell) Meiosis Makes 4 daughter cells Each cell contains half the chromosomes and is genetically unique Makes reproductive cells (gametes, sperm and egg)

Rapid Review – Level II Mitosis DNA replicates Chromatids separated Cell divides Identical cells created Meiosis I DNA replicates Homologous chromosomes separated (so only half get passed to any 1 offspring) Cell divides Chromatids separated Cell divides again 4 cells created