BiologyBiology

Meiosis

Remember from Chapter 1:CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS __________

REPRODUCE

Remember from Chapter 7, there are basically 2 types of cells__________ and ____________

EUKARYOTICPROKARYOTIC

Now let’s review Ch 10..........

Mitotic Cell Division• Mitosis makes two identical

daughter cells from one Parent cell• Bacteria and other prokaryotes

may use mitosis to reproduce – called Binary Fission

• This is asexual reproduction

ASEXUAL REPRODUCTION

Bacteria reproduce using

BINARY FISSION

This is mitosis!

Budding is used by plants and some animals to reproduce asexually (mitosis)

Regeneration is another way some animals reproduce asexually (mitosis)

Hydra

Planaria

MITOSIS

Produces cells that are __________ copies of parent cell

identical

Major Events in MitosisMajor Events in Mitosis

• Chromosome number must be maintained in animals.

• Many plants have more than two copies of each chromosome.

• Mitosis and meiosis are types of nuclear division that make different types of cells.

• Mitosis makes more diploid cells.

MITOSIS-in conclusion

•Makes ___ cells genetically _________ to parent cell & to each other

•Makes _________ cells•Makes __________•Used by organisms to:

increase size of organism, repair injuries, and replace worn out cells

2identical

2n (diploid) SOMATIC (body)

ADVANTAGES OF ASEXUAL REPRODUCTION

Can make offspring faster

Don’t need a partner

ADVANTAGES OF ASEXUAL REPRODUCTION

Works great for making new skin cells, blood cells, and any of the other body cells that need to be replaced

Our body cells are called Somatic cells (repeat word)

DISVANTAGES OF ASEXUAL REPRODUCTION

ALL ALIKENo genetic diversity within a population

One disease can wipe out whole population

Question….if not asexual, then how can

we reproduce?

Sexual Reproduction

Sexual reproduction is when two gametes (sex cells) fuse together to make a zygote.

SEXUAL REPRODUCTION

In humans, (and in many other organisms), sexual reproduction combines the genetic material from the gametes of 2 parents (sperm & egg) into a zygote

-develops into offspring that are genetically __________ from parents

DIFFERENT

• Let’s review sexual reproduction• In sexual reproduction, there are two

parents.• Each parent has a gamete, or sex cell to

donate to the offspring.• Each gamete has one set of chromosomes. • The two gametes come together

(fertilization) to form one new cell called a Zygote.

• This Zygote will grow and divide to become a unique organism.

ADVANTAGES OF SEXUAL REPRODUCTION

Allows for variation in population

Individuals can be different

Provides foundation for EVOLUTION

Allow species adapt to changes intheir environment

EGG + SPERM

If egg and sperm cells had the same number of chromosomes as other body cells . . . baby would have too many chromosomes!

MEIOSIS is the way we can avoid this problem.

Meisosis makes cells with half the number of chromosomesfor sexual reproduction

• Germ cells develop into_ gametes.– Germ cells are located in the ovaries and testes of

humans and other animals.– Gametes are sex cells:__________.– Gametes have DNA that is passed to the offspring.

sex cells

(sperm) (egg)

Sex Cells (also called germ cells)

egg and sperm

• Haploid (n) cells have one copy of every chromosome.(Remember diploid cells have two copies)–Gametes are haploid.–Human gametes have 22 autosomes and 1 sex chromosome.

Haploid cells develop into mature gametes.

• Gametogenesis is the production of gametes.• Gametogenesis differs between females and

males.

–Sperm become streamlined and motile.

–Sperm primarily contribute DNA to an embryo.

Haploid cells develop into mature gametes.

• Gametogenesis differs between females and males.

–Eggs contribute DNA, cytoplasm, and organelles to an embryo.

–During meiosis, the egg gets most of the contents; the other cells form polar bodies.

KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

DIPLOID & HAPLOIDMost cells have 2 copies of each

chromosome = ______________(one from mom; one from dad)

All BODY (___________) cells are diploid

DIPLOID 2n

HOMOLOGOUSCHROMOSOMES

SOMATIC

HOMOLOGOUS Chromosomes• SAME SIZE• SAME SHAPE• CARRY GENES for the

SAME TRAITS• BUT ______________! (Don’t have to have

the SAME CHOICES)

NOT IDENTICAL

DIPLOID & HAPLOIDSome cells have only one copy of each

chromosome = _____________Fertilization between egg and sperm

occurs in sexual reproduction.

All gametes (sperm and egg) cells are haploid

HAPLOID 1n

SO……what is a chromosome?

• main organelle involved in the Cell Cycle

• Found in the nucleus

• Contains genetic material (DNA)

• Has 2 major parts-a centromere and sister chromatids

• Your body cells have 23 pairs of chromosomes.– Homologous pairs

of chromosomes have the same structure.

– For each homologous pair, one chromosome comes from each parent.

There are two types of Chromosomes.

• Chromosome pairs 1-22 are autosomes.

• Sex chromosomes, X and Y, determine gender in mammals.

There are two types of Chromosomes.

• Humans have 46 chromosomes (23 pair)• Cats have 38 chromosomes (19 pair)• Chickens have 78 chromosomes (39 pair)• Horses have 64 chromosomes (32 Pair)• Potatoes have 48 chromosomes (24 pair)• Goldfish have100 chromosomes (50 pair)• Fruit fly has 8 (4 pair)• Corn has 20 (10 pair)• Peas have 14 (7 pair)• Mosquitoes have 6 chromosomes (3 pair)• Mice have 40 chromosomes (20 pair)• Elephants have 56 chromosomes (28)

• The zygote of humans have 23 pairs of chromosomes (or 46 individual chromosomes)

• 23 chromosomes come from each parent

• 23 + 23 = 46• Humans have 46 chromosomes

So Again……

The process of Meiosis- The

Formation of Sex Cells

• Meiosis makes haploid cells from diploid cells.

–Meiosis occurs in sex cells. –Meiosis produces gametes.

I. Introduction to Meiosis

A. Purpose - to make sex cells for reproduction.

B. Why can’t mitosis do this?

Remember….mitosis would make too many chromosomes.

MEIOSIS•Makes ____ cells

genetically different from parent cell & from each other

•Makes _____ cells•Makes ______________

•Used for ____________

4

1n Germ cellsOR Gametes (sperm & eggs)

sexual reproduction

WHAT MAKES MEIOSIS DIFFERENT ?

Crossing Over, Segregation, and Independent Assortment

ALL are ways MEIOSIS results in

=______________________________

So daughter cells are ______________from parents and from each other

different

GENETIC RECOMBINATION

WHAT MAKES MEIOSIS DIFFERENT ?

1.Homologous chromosomes pair up during ________________

= ______________SYNAPSIS

This group of FOUR (4)chromatids is called a_________________TETRAD

PROPHASE I

WHAT MAKES MEIOSIS DIFFERENT?

1. Exchange of DNA betweenhomologous pairs = _____________during PROPHASE I

CROSSING OVER

Separates gene choices and Allows shuffling of genetic material

CROSSING

OVER

• Allows for_________________in different combinations

• After crossing over, chromatid arms are________________ anymore

rearranging of DNA

NOT IDENTICAL

WHAT MAKES MEIOSIS DIFFERENT ?

Separation during ANAPHASE I-chromosome pairs separate

SEGREGATION & INDEPENDENT ASSORTMENT

SEGREGATION & CROSSING OVERtogether make even more

combinations

INDEPENDENT ASSORTMENT

INDEPENDENT ASSORTMENT

at ANAPHASE I

Lots of different combinations are possible!

This is why you don’t look exactly like your brothers and sisters even though you share the same parents!

SO WHAT MAKES MEIOSIS DIFFERENT ?

1. SYNAPSIS & CROSSING OVER (PROPHASE I)

2. SEGREGATION & INDEPENDENT ASSORTMENTin Anaphase I create genetic recombination

3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE

WHAT MAKES MEIOSIS DIFFERENT ?

3. Skip INTERPHASE II (No S) CELL DIVIDES TWICE, BUT … ONLY COPIES ITS DNA ONCE

G1 G2S P M A T C

G1

MITOSIS:

MEIOSIS:

S G2 P M A T CP M A T C

( I )

( II )

Workings of Meiosis

A. Meiosis is - the formation of sex cells (eggs and sperm)

1. Gametes - another name for sex cells.

A. Gametes have haploid chromosome number

B. Meiosis is the making of eggs and sperm with half the number of chromosomes as the parent cell.

1. Female egg = 23

2. Male sperm = 23

C. Two Main Stages of Meiosis

1. Meiosis I a. Prophase I b. Metaphase I c. Anaphase I d. Telophase I

2. Meiosis II

a. Prophase II

b. Metaphase II

c. Anaphase II

d. Telophase II

D. There is only one interphase

Cells go through two rounds of division in meiosis.

• Meiosis reduces chromosome number and creates genetic diversity.

• Meiosis I and meiosis II each have four phases, similar to those in mitosis.

homologous chromosomes

sisterchromatid

s

sisterchromatid

s

– Pairs of homologous chromosomes separate inmeiosis I.

– Homologous chromosomes are similar but not identical.

– Sister chromatids divide in meiosis II.– Sister chromatids are copies of the same

chromosome.

• Meiosis I occurs after DNA has been replicated.• Meiosis I divides homologous

chromosomes in four phases.

• Meiosis II divides sister chromatids in four phases.

• DNA is not replicated between meiosis I andmeiosis II.

Meiosis I

A. Interphase

1. Replication of chromosomes occurs.

2. This is the only interphase.

B. Prophase I

1. Chromatids appear

2. Centrioles split.

3. Centrioles move to the opposite poles.

4. Spindle fibers appear

5. Nucleolus disappears

6. Nuclear membrane disappears

7. Tetrads form - two pairs of homologous chromosomes joining together.

8. Crossing-over occurs here - genes are exchanged between homologous chromsomes.

a. Creates variation in new offspring

C. Metaphase I

1. Tetrads line up at the equator.

D. Anaphase I

1. Tetrads separate.

2. Chromatids are pulled to the opposite poles.

E. Telophase I

1. Chromatids still visible.

2. Nucleolus and Nuclear Membrane reforms.

3. Centrioles replicate

4. Two new cells.

IV. Meiosis IIA. No interphase begins this

phase. 1. 2 cells with the haploid

chromosome number begin this stage.

2. Meiosis II will always have two cells in each phase.

B. Prophase II 1. Nuclear membrane and

nucleolus disappear. 2. Centrioles split 3. Centrioles move to the

poles.

4. Spindle fibers form.

5. Chromatids are visible and attach to spindle fibers.

C. Metaphase II

1. Chromatids line up on the equator.

D. Anaphase II

1. Centromeres separate.

2. Chromotids are pulled to opposite poles.

E. Telophase II

1. Centrioles replicate

2. Nuclear membrane and nucleolus reappear.

3. Spindle fibers disappear.

4. 4 new cells are formed

a. Only have half the number of chromosomes as the parent cell.

b. Males - all 4 remain alive and viable.

c. Females – one egg grows rest (polar bodies) die off.

V. Meiosis-Mitosis Comparison

A. Mitosis

1. 4 phases

2. Produces 2 diploid cells

3. Daughter cells identical to parent

B. Meiosis

1. 8 phases

2. 4 haploid cells produced

3. Daughter cells not identical to parent

4. Contain tetrads and crossing-over.

• Meiosis differs from mitosis in significant ways.

– Meiosis has two cell divisions while mitosis has one.

– In mitosis, homologous chromosomes never pair up.

– Meiosis results in haploid cells; mitosis results in diploid cells.

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

That’s All For Now Folks!