CELLULAR REPRODUCTIONCELLULAR REPRODUCTION

This is the making of cells

--not necessarily making babies

HEY YOU WANNASPLIT?

Ok!

Why do Cells Divide?Why do Cells Divide?

• 1. maintain surface area to volume ratio

• 2. growth of organism

• 3. repair damaged areas

• 4. replace worn out cells

• 5. pass on genetic information

2 Forms of Cellular Division2 Forms of Cellular Division

• Asexual Reproduction

• Sexual Reproduction

Asexual Reproduction Asexual Reproduction

• production of new cells from one parent cell

• offspring cells identical to parent cell

• can make new cells or an entire organism

Asexual production of whole Asexual production of whole organismsorganisms

1. BINARY FISSION-cell divides into two equal cells

-occurs in bacteria and blue-green algae

and paramecia

2. SPORES-groups of cells form inside parent

-cells burst out of parent and grow into new organisms

-occurs in fungus and ferns

3. BUDDING-division into two unequal parts

-smaller cell will then grow to size of parent

-occurs in fungus (yeast) and hydras

4. VEGETATIVE PROPAGATION-part of the parent will break off and grow

into a completely new organism

-common in plants

(spider plants, potatoes)

Asexual reproduction for growth, Asexual reproduction for growth, repair, and replacement of cellsrepair, and replacement of cells

• Terms To Know

• CHROMOSOME: structure that contains the DNA

• CHROMATIN: thin, stringy form of DNA where the molecule is relaxed and unwound into thread-like fibers

• CENTROMERE: the point where sister chromatids are connected

CHROMATID: the tightly wound, visible form of a chromosome

SISTER CHROMATIDS: 2 identical chromosomes, the original and its copy

Chromosome Structure

How many chromosomes do How many chromosomes do we have?we have?

• 46- (23 pairs)- called the diploid number (2n=46)

• Where did these come from?

• Each Pair= 1 from mom & 1 from dad

Asexual reproduction for Asexual reproduction for growth, repair, and replacement growth, repair, and replacement

of cellsof cells

• Cells go through a cell cycle

• Then………

• Cells split to form new cells and maintain chromosome number

BRAINTEASERBRAINTEASER

• If each cell has 46 chromosomes, what has to happen each time before a cell divides?

The Cell CycleThe Cell Cycle

Fig. 9.3, p. 151

InterphaseInterphase

• stage of growth / preparation for division

• lasts about 21 hours

• DNA in Chromatin

form

• 3 stages: G1, S, G2

Stages of InterphaseStages of Interphase

• G1- period of growth / development• S (synthesis) duplicates DNA (chromosomes)

– still in chromatin phase

• G2 duplicates cytoplasm and organelles

HOW DO CELLS DIVIDE?HOW DO CELLS DIVIDE?

Answer= MITOSIS

Mitosis completes the cell cycleMitosis completes the cell cycle

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

ProphaseProphase• chromosomes become visible chromatids

• sister chromatids form (seen as X)

• microtubules form from a spindle at opposite ends of the cells

• spindle arises from centrioles

• nuclear envelope disappears

By the end of By the end of prophase…prophase…

• microtubules have attached to centromeres

• sister chromatids being pulled toward center of cell

MetaphaseMetaphase

• microtubules pull chromatids to center

• chromatids align along the center of cell

AnaphaseAnaphase

• Chromosomes split at centromeres

• microtubules pull apart chromosomes

• Chromosomes

(chromatids) begin migrating to opposite ends of cell

TelophaseTelophase

• Chromatids arrive at poles

• nuclear envelope reforms around chromatids

• chromatids unwind into chromatin

• spindle disintegrates

• cell membrane begins forming in center

CytokinesisCytokinesis

• cell membrane finishes splitting the cell

• 2 daughter cells are formed

• cells will be slightly smaller than parent cell

TELOPHASE PROPHASE

ANAPHASEMETAPHASE

nucleus

cytoplasm

one spindle pole

one spindle pole

one of the condensed chromosomes

spindle equator

microtubules organized as a spindle apparatus

Plant Mitosis

INTERPHASE

nucleus

plasmamembrane

pair ofcentrioles

cell chromosomes

nuclearenvelope

microtubules

CELL AT INTERPHASE EARLY PROPHASE LATE PROPHASE PROMETAPHASE

Fig. 9.5a, p. 152

Animal Mitosis

METAPHASE ANAPHASE TELOPHASE INTERPHASE

Fig. 9.5b, p. 153

Sexual ReproductionSexual Reproduction

• Key Facts

• sex cells are formed – called Gametes (Meiosis)

• fertilization results in offspring

• offspring exhibits traits of both parents

Points of InterestPoints of Interest

• all cells contain 2 of each chromosome- 1 from mom and 1 from dad

• each of the pair carries identical genes• variation exists in the outcome of the genes

– example: eye color

• humans have 46 chromosomes (23 pairs)• 22 pairs are called autosomes• The 23rd pair is the sex chromosomes (X and Y)• Males= XY Females= XX

More TermsMore Terms

• DIPLOID: the total number of chromosomes a species carries– often abbreviated as 2n – found only in parent cells

• HAPLOID: half the number of chromosomes for a species– often abbreviated as n– found in sex cells (egg/sperm) formed from

meiosis

• HOMOLOGOUS CHROMOSOME: 2 chromosomes which are the same (1 from mom 1 from dad)

– Both found in diploid cells– often described as “homologues”

• GAMETE: the sex cell formed from meiosis– haploid condition– egg or sperm

MEIOSISMEIOSIS

• begins with the cell cycle• 2 Phases

– MEIOSIS I– MEIOSIS II

• Occurs only in Gonads- testes and ovaries• Remember-Mitosis occurs in all other

Somatic (body) cells• Reduces the number of chromosomes by

half

InterphaseInterphase

• a stage of growth and preparation for division of nucleus

• DNA is in Chromatin form

• 3 stages: G1, S, G2

• the DNA(chromosomes) does double

MEIOSIS IMEIOSIS I

• very similar to Mitosis

• stages include– Prophase I

– Metaphase I– Anaphase I– Telophase I

– Interkinesis**

Prophase IProphase I

• chromatin shortens and thickens into chromatids (sound familiar?)

• since there are 2 of each chromosome, the 2 homologous chromosomes pair up to form a TETRAD *(does not happen in Mitosis)

Brain TeaserBrain Teaser

• You are the world’s leading tomato researcher. You have located the gene in a tomato’s DNA that produces lycopene, a natural chemical that helps fight heart disease. The gene is on chromosome 10. If a tomato has a diploid # (2n) of 24, how many tetrads will you have to search through during prophase 1 until you locate chromosome 10?

Metaphase IMetaphase I

• the tetrads will align along the center- similar to mitosis

• Different arrangements can be formed- see example on board

Anaphase IAnaphase I

• the tetrads break

• one of each chromosome and its sister chromatid will remain attached

• the sisters will migrate toward the poles

Telophase ITelophase I

• cytoplasm will separate as in Mitosis

• the sisters remain attached at the centromere

• chromatids do not relax into chromatin

InterkinesisInterkinesis

• the DNA is not duplicated

• this is a period between 2 phases

• each cell has completed the first division

• each cell is haploid (n)

Fig. 10.4a p. 164

plasmamembrane

newlyformingmicrotubulesin thecytoplasm

spindleequator(midwaybetween thetwo poles)

one pair ofhomologouschromosomes

PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I

MEIOSIS I

then…MEIOSIS IIthen…MEIOSIS II

• similar steps occur again except the cell is going to split the sister chromatids into two sets

• *no Interphase II• stages include

– Prophase II– Metaphase II– Anaphase II– Telophase II– Cytokinesis

but...but...

• in Anaphase II, the sister chromatids are split apart

• one of each migrates to opposite poles

• during Telophase II, the nucleus forms around the chromosomes (chromatids)

• chromatids relax into chromatin

Fig. 10.4b p. 165

PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II

MEIOSIS II

Cell Division has finishedCell Division has finished

• the “daughter” cells produced are in the haploid condition

• 1 cell has now produced 4 haploid daughter cells

• they need to be finished

Formation of the Egg and Formation of the Egg and SpermSperm

• In Females-

• OOGENESIS - formation of the egg– 1 cell makes 4 daughter cells– only 1 daughter becomes the egg– cell division is not equal -3 become POLAR

BODIES– all will be haploid

• SPERMATOGENESIS - formation of sperm– 1 cell makes 4 equal sized daughter cells– all 4 will be sperm– all will be haploid

FertilizationFertilization

• is not part of cell division

• occurs when an egg and sperm meet

• a ZYGOTE forms from the meeting

• the zygote is 2n- chromosomal number is restored

Function of FertilizationFunction of Fertilization

• produces new offspring

• introduces mutations for survival

• increases variation in a population

TwinsTwins

• 2 Types• Identical- always same sex- after being

fertilized, zygote splits spontaneously and both begin dividing (MONOZYGOTIC)– Identical DNA

• Fraternal- 2 eggs are present to be fertilized- can be same or different sexes- appear different because DNA is different (DIZYGOTIC)