Meiosis

Make a cover page:

•Your Name

•Chapter 11

•Meiosis

Feel free to decorate your cards as you

go!

• Diploid– 2 sets of chromosomes in

a cell.

– ½ from mom, ½ from dad.

– 2n

– All body cells are diploid.

– Made by MITOSIS.

• Haploid– 1 set of chromosomes

in a cell.

– 1n

– All sex cells are haploid.

– Made by MEIOSIS.

(2 separate flashcards)

DIPLOID vs. HAPLOID

1n + 1n = 2n

egg + sperm = new organismHaploid + Haploid = DIPLOID

Not a flashcard.

Gametes• Another name for sex cells: egg & sperm

Zygote

• A fertilized cell.

• 2 gametes that are now together.

In case you’ve never seen it for real…this is human DNA.

Not a flashcard.

23 Homologous pairs – one from mom and one from dad

This is a DIPLOID cell’s DNA. (2n)Not a flashcard.

To do this, MITOSIS is used.

This is a HAPLOID cell’s DNA. (1n)Not a flashcard.

To do this, MEIOSIS is used.

Meiosis• The making of gametes (eggs & sperm).

• Cells contain ½ the normal amount of chromosomes. (haploid)

Meiosis

Why is meiosis necessary?

• If the sex cells didn’t have ½ the amount of chromosomes, what would happen when the sperm & egg made a zygote?

• Answer: Each baby would have twice the number of chromosomes as the parents!!!

26 + 26 = 52!

egg spermzygote

WOW! That’s 2 full sets!

What is produced in meiosis?

• 4 haploid cells (1n)

• Each cell is genetically different! Cool!

The cells produced during meiosis have DIFFERENT DNA!

Not a flashcard.

Review Meiosis Facts• Makes ____ cells genetically

different from parent cell & from each other

• Makes _____ cells (1n or 2n?)

• Makes ________________

• Used for ______________

4

1n

Gametes (sperm & eggs)

sexual reproduction

Not a flashcard.

Spermatogenesis• Makes 4 sperm cells.

Oogenesis• Makes 1 egg. (and 3 polar bodies)

Spermatogenesis vs. Oogenesis

Not a flashcard.

What is different about meiosis?

• Many different variations in the gametes.

___________________________________

• Divides twice, but only copies DNA once.

___________________________________

Makes cells with different genes than parent cell

Makes cells with ½ the number of chromosomes as parent cell

Not a flashcard.

Phases of Meiosis

I P M A T P M A T

Meiosis 1 Meiosis 2

(I Peed on the MAT twice!)

Meiosis

Meiosis

I P M A T

P M A T

cytokinesis

cytokinesis

Mitosis vs MeiosisInterphase Interphase I

• DNA spread out as chromatin• Nuclear membrane visible• DNA copied during S phase Same as mitosis!

Mitosis vs Meiosis Prophase Prophase I

• DNA scrunches into chromosomes

• Nuclear membrane disappears

• Centrioles appear

Same, except… Homologous pairs match up

XX

XX

XX

X

X

X

Crossing Over

• Chromatid arms trade DNA with each other.

• Produces daughter cells with different gene combinations.

Mitosis vs Meiosis Metaphase Metaphase I

• Chromosomes line up in middle

Chromosomes line up in middle with homologous partner

Mitosis vs Meiosis Anaphase Anaphase I

• Chromatids split and move apart.

•Chromatids stay together•Homologous pairs move apart

Mitosis vs Meiosis Telophase Telophase I

• Two nuclei• Nuclear membrane returns• DNA spreads out as

chromatin

Same as mitosis!

Mitosis vs Meiosis Cytokinesis Cytokinesis I

• Cytoplasm splits into 2 cells Same as mitosis!

Mitosis vs Meiosis Prophase Prophase II

• DNA scrunches into chromosomes

• Nuclear membrane

disappears• Centrioles appear

Same as mitosis!

Mitosis vs Meiosis Metaphase Metaphase II

• Chromosomes line up in middle

Same as mitosis!

Mitosis vs Meiosis Anaphase Anaphase II

• Chromatids split and move apart

Same as mitosis!

Mitosis vs Meiosis Telophase Telophase II

• Two nuclei• Nuclear membrane

returns• DNA spreads out as

chromatin

Same as mitosis!

Mitosis vs Meiosis Cytokinesis Cytokinesis II

• Cytoplasm splits Same as mitosis!

Mitosis vs MeiosisIn Meiosis:

• (Prophase I) Homologous pairs match up.

• (Prophase I) Crossing over creates

genetic differences.

• Cells divide twice but only copies DNA once- this makes haploid cells.

Meiosis

The end. Really. • Test date:

• How to succeed on GHS biology tests:– Memorize the flashcards.

• Practice with friends, by yourself, or with family.

– Read the book.• It is easy reading.

• Reading the text helps you understand the written part.

– Do all labs, homework, and worksheets.• If you missed any days, make sure you made up any work!