Warm-Up Questions 1. What are the stages of mitosis in order?2. The diagram represents a cell process.

Which statement regarding this process is true?A. Cell B contains the same genetic information that cells A and C

containB. Cell C has DNA that is only 50% identical to cell BC. Cell A has DNA that is only 75% identical to cell CD. Cells A, B, and C contain completely different genetic information

3. How many chromosomes do most human cells have?

Warm-Up Questions: Check your answers 1. What are the stages of mitosis in order?

2. The diagram represents a cell process.

Which statement regarding this process is true?A. Cell B contains the same genetic information that cells A and C containB. Cell C has DNA that is only 50% identical to cell BC. Cell A has DNA that is only 75% identical to cell CD. Cells A, B, and C contain completely different genetic information

3. How many chromosomes do most human cells have?

Prophase, Metaphase, Anaphase, and Telophase

A

46 total chromosomes

FYI: 1. The Cell Division test is on Friday!

2. The midterm is next Wednesday!

2006-2007

Meiosis &

Sexual Reproduction

Cell division / Asexual reproduction

• Mitosis (asexual reproduction)– produces cells with same information

• identical daughter cells

– exact copies• clones

– same number of chromosomes• same genetic information

-used by single cell organisms and somatic (body) cells

• like bacteria or skin cells

Aaaargh!I’m seeingdouble!

How about more complex organisms?

1. Mitosis is good for simple organisms, but what if a complex multicellular organism (like us) wants to reproduce?

– joining of egg + sperm (fertilization)

2. Do we make egg & sperm by mitosis?

46 46+ 92

egg sperm zygote

What if we did, then….

Doesn’t work!

No!

3. Meiosis makes sperm & eggs

4. In humans: 46 homologous chromosomes to 23 single chromosomes (half the number of chromosomes)

23

2346

egg

sperm

46

meiosis

haploiddiploid

5. What are Paired/ Homologous chromosomes?

• Homologous chromosomes

– both chromosomes of a pair carry “matching” genes

• control same inherited characters

• 6. homologous = same information

diploid

2n

2n = 4

homologous

chromosomes

double stranded

homologous chromosomes

eye color

(brown?)

eye color

(blue?)

7. Egg cells and sperm cells are called “haploid” because they

only have a single set of chromosomes.

8. Diploid vs. Haploid Cell Diploid

• full set of chromosomes (2n)

• mitosis

• all cells but gametes (sex cells)

Haploid

• half set of chromosomes (n)

• meiosis

• gametes only

9. How do we create haploid cells?Meiosis = reduction division

10. Meiosis

A. special cell division in sexually reproducing organisms

B. reduce number of chromosomes

• 2n 1n

• diploid haploid

– half

C. makes gametes

• sperm, eggs

What actually happens during meiosis?

gametes

11. How do we make sperm & eggs?

• Must reduce 46 chromosomes 23– must half the number of chromosomes

– haploid

23

2346

egg

sperm

46

meiosis 46

fertilization

23

23

zygote

12. Meiosis I (very similar to mitosis)

Copy DNA

and

crossing

over

occurs

Chromosomes

Line Up Cell Divides

12. Meiosis II (2): Kind of like meiosis I, except the DNA doesn’t replicate before

Chromosomes

Line Up

Cell Divides

12. It looks like this when it’s combined

13. Meiosis Summary:Interphase: Before meiosis begins, genetic material is duplicated. First division of meiosis (Meiosis I)

– Prophase 1: DNA condenses into chromosomes. Crossing-over can occur during the latter part of this stage.

– Metaphase 1: Homologous chromosomes align in the middle (Meta=middle)

– Anaphase 1: Homologous pairs separate and move towards the poles.

– Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

Second division of meiosis: Gamete formation(Meiosis II)

– Prophase 2: DNA does not replicate. – Metaphase 2: Chromosomes align at

the equatorial plate (in the middle). – Anaphase 2: Sister chromatids migrate

separately to each pole. – Telophase 2: Cell division is complete.

Four haploid daughter cells are obtained.

How does meiosis lead to a new organism?

mitosis

zygote

14. How does meiosis lead to a new organism?

23

2346

egg

sperm

46

meiosis 4623

23

fertilization mitosis &development

meiosis fertilization mitosis + development

46

46

46

46

46

46

46 46

gametes

15. Cycle of Life: (when do the different

types of cell division happen during our lives?)

Fertilization: When an egg cell and a sperm cell join together

What do these 46 human chromosomes look like in real life?

16. “Karyotypes” are used to see the number and appearance of the chromosomes an organism has

Random Fact:• The sperm cell (male sex cell) determines the sex of

the offspring. The 23rd chromosomes (X or Y) is the genetic difference between men and women.

Karyotype: Human Female (Female because it has two X chromosomes, no Y)

Notice:

There are 23 pairs of chromo-somes

23x2=46 total

‘RE

Karyotype: Human Male (Male because it has X and Y chromosomes)

Notice:

There are 23 pairs of chromo-somes

23x2=46 total

17. How does meiosis increase genetic variation?

1.

2.

3.

How does meiosis create genetic variation?

18. Advantages of Meiosis- it increases genetic variation

No two offspring (except identical twins) are the same, giving the species a better chance of surviving.

19. Disadvantage of Meiosis-organisms cannot reproduce by themselves, and it takes more time and energy to reproduce/ find a partner to reproduce with.

Congrats! You finished the notes!Now, please flip your note paper to

the back:1)Use the last two slides (scroll

down) to help you answer the other review questions on the paper.

Meiosis & mitosis

• Meiosis to make gametes

– sperm & egg

• Mitosis to make copies of cells

– growth

– repair

– development

Reproduction Review:Sexual Reproduction

· 2 parents - male and female

· involves gametes - sperm and egg

· offspring genetically different

· can be internal or external fertilization

· MEIOSIS

Asexual Reproduction

· 1 parent

· offspring produced by a “part” or “division” of the parent

· CLONES - offspring genetically identical

· MITOSIS