MEIOSISHONORS BIOLOGY

Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia

BINARY FISSION & MITOSIS

Produces cells that are genetically __________ copies of parent cellidentical

Asexual vs. Sexual Reproduction

In asexual reproductionOne parent produces genetically identical

offspring by mitosis Ex: body cells (mitosis), budding, binary fission,

spores, etc.

ParentBud

0.5 mm

ADVANTAGES OF ASEXUAL REPRODUCTION

• Can make offspring faster

• Don’t need a partner; only 1 “parent” needed

DISVANTAGES OF ASEXUAL REPRODUCTION

• ALL ALIKE (“clones”)

• Species usually CAN’T change and adapt

• One disease can wipe out whole population

SEXUAL REPRODUCTION

• Combines genetic material from 2 parents (sperm & egg)

• Offspring are genetically different and unique from parents

• Different type of cell division must be used to create an egg & a sperm! (meiosis)

ADVANTAGES OF SEXUAL REPRODUCTION

• Allows for variation in population • Individuals can be different• Provides foundation for EVOLUTION

• Allow species adapt to changes in their environment

Groups of Cells in our Body

• Somatic Cells: – Body Cells– Every cell in your body, except for your sex cells

(eggs and sperm)– Divide by Mitosis

• Gametes:– Sex cells (reproductive cells) (eggs and sperm)

EGG + SPERM

If egg and sperm had same number of chromosomes as other body cells (2n) . . . baby would have too many chromosomes!

MEIOSIS is the way…

to make cells with ½ the number of chromosomesfor sexual reproduction

http://waynesword.palomar.edu/lmexer2a.htm

• Different species have different number of chromosomes– Autosomal Chromosomes – code for physical

traits (in pairs)– Sex Chromosomes - gender (in pairs)– How many chromosomes do Humans have?

• 46 (23 pairs of chromosomes) • 22 are autosomal pairs and 1 pair are sex

chromosomes

What are sex chromosomes?• Sex Chromosomes:

– Determines sex (male/female)– 2 forms

• X and Y• Males: XY• Females: XX

DIPLOIDMost cells have 2 copies of each

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

All BODY (________ ) cells are diploid

DIPLOID 2n

HOMOLOGOUSCHROMOSOMES

SOMATIC

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HOMOLOGOUS – pair of chromosomes that are the same size, shape, and gene pattern

- 23 homologous pairs = 46 chromosomes

(note: NOT identical – one from each parent)

One pair of homologous chromosomes = tetrad

HAPLOID

Some cells have only one copy of each chromosome = _____________

All sperm and egg cells are haploid

HAPLOID 1n

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

• Makes ___ cells• Makes __________• Used by organisms to: increase size of organism,

repair injuries, replace worn out cells

http://waynesword.palomar.edu/lmexer2a.htm

2identical

2n

SOMATIC (body)

MEIOSIS• Makes ____ daughter cells

genetically different from parent cell & from each other

• Makes _____ cells• Makes ______________

• Used for ____________

– Goal: each daughter cell has half the number of chromosomes as parent cell

– Occurs in sex organs (testes, ovaries)

4

1n Gametes

(sperm & eggs)

Sexual reproduction

http://waynesword.palomar.edu/lmexer2a.htm

What is Fertilization?

• Fertilization:– Haploid (n) sperm cell and haploid egg cell fuse

together – Creates a Zygotewhich is a fertilized egg and is diploid(2n)

Diploid Female(2n=46)

Sperm Cell(n=23)

Zygote(2n=46)

MEIOSIS

FERTILIZATION

MITOSIS

Diploid Male(2n=46)

Egg Cell(n=23)

Embryo(2n=46)

What is the difference between Meiosis and Mitosis?

MITOSIS MEIOSIS

2 daughter cells same number of chromosomes as parent cell

4 new offspring cells with half the number of chromosomes as parent cell

Genetically identical Exchange of material between homologous chromosomes

2 Cell Divisions in Meiosis

– Meiosis I• Separates

Homologous Pair

– Meiosis II• Separates sister

chromatids

What are the stages in Meiosis?MEIOSIS I• Prophase I• Metaphase I• Anaphase I• Telophase I

MEIOSIS II• Prophase II• Metaphase II• Anaphase II• Telophase II

WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS?

1.Homologous chromosomes pair up during ________________

= ______________called SYNAPSIS

Images modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

This group of FOUR (4)chromatids is called a_________________TETRAD

PROPHASE I

WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS?

1. Exchange of DNA betweenhomologous pairs = _____________during PROPHASE I

CROSSING OVERAllows shuffling

of genetic material called genetic recombination

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

SUMMARY: HOW MANY CHROMOSOMES ARE IN A HUMAN CELL DURING PROPHASE I?

46 CHROMOSOMES2n 23 homologous pairs

CROSSING OVER

• Allows for_________________in different combinations

• After crossing over, chromatid arms are________________ anymore

http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

rearranging of DNA

NOT IDENTICAL

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Crossing Over – in Prophase

2 karyokinesis events occur in meiosis!

What happens during Metaphase I and Anaphase I?

• Metaphase I:– Tetrads line up in the

middle of the cell

• Anaphase I:– Homologous pairs

(tetrads) split and move to opposite poles of cell

What happens during Telophase I?• Telophase I:

• Spindle fibers disappear• Nucleus envelope reappears• Cytokinesis

– 2 Haploid daughter cells (1n)

Now we have 2 daughter cells going through Meiosis II…….What happens during Meiosis II?

• Prophase II• Metaphase II• Anaphase II• Telophase II

Section 11-4

Figure 11-15 Meiosis

Meiosis I

PHASES OF MEIOSIS

= MAJOR differences from mitosis

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 II

The 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 IIMeiosis II: NOTE- no Interphase II

MITOSIS vs. MEIOSISINTERPHASE INTERPHASE I

• DNA is spread out as chromatin• Nuclear membrane/nucleolus visible• DNA is copied during S phase• Makes stuff new cell needs in G2

• Cell Grows

SAME AS MITOSIS

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

2n cell2n cell

MITOSIS vs. MEIOSIS PROPHASE PROPHASE I

• DNA packs into chromosomes• Nuclear membrane/

nucleolus disappear• Spindle fibers appear and

attach to chromosomes• Centrosomes migrate to poles

• DNA packs into chromosomes• Nuclear membrane/ nucleolus

disappear• Spindle fibers appear and attach to

chromosomes• Centrosomes migrate to poles SYNAPSIS and CROSSING

OVER OCCURS

2n cell

2n cell

MITOSIS vs. MEIOSIS METAPHASE METAPHASE I

• Chromosomes line up in middle in single file line

•Chromosomes line up in middle with homologous partner•Independent assortment occurs

2n cell2n cell

MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE I

• Polar fibers lengthen cell• Chromatids split •Polar fibers lengthen cell

•Chromatids stay togetherHomologous pairs split (SEGREATION OCCURS)

2n cell2n cell

MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE I

• See TWO nuclei• Nuclear membrane/ nucleolus return• DNA spreads out as chromatin• Spindle fibers disappear

SAME AS MITOSIS

n cell2n cell

MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS I

Cytoplasm splits into 2 daughter

cells

SAME AS MITOSIS

n cell2n cell

DIPLOIDDIPLOID HAPLOIDHAPLOID

MITOSIS vs. MEIOSIS INTERPHASE II

• DNA is spread out as chromatin• Nuclear membrane/nucleolus visible• DNA is copied during S phase• Makes stuff new cell needs in G2

• Cell Grows

SKIP INTERPHASE II

DNA NOT COPIED

2n celln cell

MITOSIS vs. MEIOSIS PROPHASE PROPHASE II

• DNA packs into chromosomes• Nuclear membrane/ nucleolus

disappear• Spindle fibers appear and attach to

chromosomes• Centrosomes migrate to poles

SAME AS MITOSIS

(but cell is now HAPLOID)

n cell

2n cell

MITOSIS vs. MEIOSIS METAPHASE METAPHASE II

• Chromosomes line up in middle in a single file line

SAME AS MITOSIS (but cell is now HAPLOID)

2n cell n cell

MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE II

Chromatids split and move apart

2n celln cell

SAME AS MITOSIS (but cell is now HAPLOID)

MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE II

• See TWO nuclei• Nuclear membrane/

nucleolus return• DNA spreads out as

chromatin• Spindle fibers disappear

SAME AS MITOSIS (but cell is now HAPLOID)

2n cell n cell

MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS II

Cytoplasm splits

http://www.pbs.org/wgbh/nova/baby/divi_flash.html

SAME AS MITOSIS (but cell is now HAPLOID)

RESULTS IN TWO2n cell

RESULTS IN FOURn cell

Ways Meiosis is different?

• 2nd and 4th animations– http://highered.mcgraw-hill.com/sites/0072437316/stu

dent_view0/chapter12/animations.html#

MAKING SPERM & EGGS

Putting it all together…

46

egg

sperm

4646

23

23

meiosis fertilization mitosis + development

46

46

46

46

46

4646 46

49

• Karyotype:– Display of

chromosomes (condensed)

What is a Karyotype?

51

Human Karyotype -

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What’s different? (Down Syndrome)

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Klinefelter’s Syndrome

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Turner Syndrome