Chapter 8: Cell ReproductionChapter 8: Cell Reproduction

Original slide set from: www.laney.edu/wp/laura_coronado/files/2011/08/SVChap-8.ppt

STANDARDSSTANDARDS•SPI 3210.1.6 - Describe the relationship between the cell cycle and reproduction.

• - I can determine the movement of chromosomes during cell reproduction.

With your partnerWith your partner

•Find two different definitions of “chromosome”

CHROMOSOME STRUCTURECHROMOSOME STRUCTURE

●Chromosome definition:in a eukaryotic cell, one of the structures in the nucleus that are made up of DNA and protein; in a prokaryotic cell, the main ring of DNA

ChromosomesChromosomes

●What do they look like?

●How many do humans have?

They look like an “X” just before the cell divides and an “I” after they divide.

46 chromosomes (23 from mom, 23 from dad)

With your partnerWith your partner

•Explain the difference in the two shapes of chromosomes

CHROMOSOME VOCABULARYCHROMOSOME VOCABULARY

●Histones:

●Chromatid:

●Centromere:

a type of protein found in the chromosomes of eukaryotic cells but not prokaryotic cells.

one side of a chromosome that become visible during meiosis or mitosis

The region of the chromosome that holds the two sister chromatids together during mitosis

CHROMOSOME OR CHROMATIN?

CHROMOSOME OR CHROMATIN?

●Chromosome:

●Chromatin:

Tightly coiled DNA & proteins during cell division; DNA cannot be “read” while in this form.

Loosely coiled DNA & proteins during the cell’s life other than cell division. DNA can be “read” to direct activities of the cell.

WITH YOUR PARTNER:WITH YOUR PARTNER:

●Do more complex organisms have more chromosomes?

What is cell reproduction?What is cell reproduction?

WHAT CELL REPRODUCTION ACCOMPLISHES

WHAT CELL REPRODUCTION ACCOMPLISHES

Reproduction:• May result in the birth of new

organisms• More commonly involves the

production of new cells

Cell DivisionCell Division

Cell division plays important roles in the lives of organisms. •Replaces damaged or lost cells• Permits growth• Allows for reproduction

Cell Replacement Growth via Cell DivisionFUNCTIONS OF CELL DIVISION

Human kidney cell Early human embryo

LMColo

rized

TEM

Figure 8.1a

Asexual ReproductionAsexual Reproduction

• Single-celled organisms reproduce by simple cell division

• There is no fertilization of an egg by a sperm

• The parent and its offspring have identical genes.

Asexual ReproductionAsexual Reproduction

Binary FissionBinary Fission• Prokaryotic cells divide through a Prokaryotic cells divide through a

simple form of division calledsimple form of division called Binary FissionBinary Fission

• 3 step process3 step process• Single “naked” strand splits and Single “naked” strand splits and

forms a duplicate of itself.forms a duplicate of itself.• The two copies move to opposite The two copies move to opposite

sides of the cellsides of the cell• Cell “pinches” into two new and Cell “pinches” into two new and

identical cells called identical cells called ""daughter daughter cellscells". (Cell wall then forms if ". (Cell wall then forms if applicable)applicable)

Asexual ReproductionAsexual Reproduction

• Mitosis is the type of cell division responsible for: Asexual reproduction Growth and maintenance of multicellular organisms Some multicellular organisms, such as sea stars, can

grow new individuals from fragmented pieces. Growing a new plant from a clipping

Asexual ReproductionFUNCTIONS OF CELL DIVISION

Sea stars

LM

Amoeba African Violet

Figure 8.1b

Sexual ReproductionSexual Reproduction

Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

Thus, sexually reproducing organisms use:• Meiosis for reproduction • Mitosis for growth and maintenance

Chromosomes

LM

Figure 8.3

ChromosomesChromosomes

Chromosomes:• Are made of chromatin, a combination of

DNA and protein molecules• Are not visible in a cell until cell division

occurs–Before a parent cell splits into two, it

duplicates its chromosomes

Number of chromosomesin body cells

Indian muntjac deer

Species

Opossum

Koala

Human

Mouse

Giraffe

Buffalo

Dog

Red viscacha rat

Duck-billed platypus

102

78

60

54

46

40

30

22

16

6

Figure 8.2

Eukaryotic Cell Genetic Information

Eukaryotic Cell Genetic Information

Most genes on chromosomes in cell nucleus A few genes found in mitochondrial and

chloroplast DNA Each chromosome: one very long DNA

molecule, typically with thousands of genes. Histones are proteins used to package DNA. Nucleosomes consist of DNA wound around

histone molecules.

Duplicated chromosomes(sister chromatids) TE

M

Tight helical fiber

Looped domains

TEM

Centromere

Nucleosome

“Beads ona string”

Histones

DNA double helix

Figure 8.4Laura Coronado Bio 10 Chapter 8

Duplicated chromosome

Chromosome (onelong piece of DNA)

Centromere

Sisterchromatids

Figure 8.UN2Laura Coronado Bio 10 Chapter 8

ChromosomesChromosomes Before a cell divides, it duplicates all of its

chromosomes, resulting in two copies called sister chromatids.

Sister chromatids are joined together at a narrow “waist” called the centromere.

When the cell divides, the sister chromatids separate from each other.

Once separated, each chromatid is:• Considered a full-fledged chromosome • Identical to the original chromosome

Chromosomeduplication

Sisterchromatids

Chromosomedistribution todaughter cells

Figure 8.5Laura Coronado Bio 10 Chapter 8

The Cell CycleThe Cell Cycle

A cell cycle is the orderly sequence of events that extend from the time a cell is first formed from a dividing parent cell to its own division into two cells.

The cell cycle consists of two distinct phases:• Interphase• The mitotic phase

Cytokinesis(division ofcytoplasm)

Mitosis(division of nucleus)

Mitotic (M) phase:cell division

(10% of time)

Interphase: metabolism andgrowth (90% of time)

S phase (DNA synthesis;chromosome duplication)

G1 G2

Figure 8.6Laura Coronado Bio 10 Chapter 8

InterphaseInterphase

Interphase Interphase

Most of a cell cycle is spent in interphase. During interphase, a cell:• Performs its normal functions• Doubles everything in its cytoplasm• Grows in size

Laura Coronado Bio 10 Chapter 8

InterphaseInterphase

• Interphase 3 Stages

• G1 (Gap 1)G1 (Gap 1) Phase Phase - Cell performs its normal function (cells which do not - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span)divide stay in this stage for their entire life span)

• -cells grow and mature-cells grow and mature• S (Synthesis) PhaseS (Synthesis) Phase - Here the cell actively duplicates its DNA in - Here the cell actively duplicates its DNA in

preparation for divisionpreparation for division• G2 (Gap 2) PhaseG2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases - Amount of cytoplasm (including organelles) increases

in preparation for division.in preparation for division.• Another possibilityAnother possibility

§ G0 PhaseG0 Phase cells do not prepare for cell divisioncells do not prepare for cell division• Generally straight from G1 phaseGenerally straight from G1 phase• Example: fully developed cells in Central Nervous System never divide againExample: fully developed cells in Central Nervous System never divide again

MitosisMitosis

MitosisMitosis

The mitotic (M) phase includes two overlapping processes:• Mitosis, in which the nucleus and its

contents divide evenly into two daughter nuclei • Cytokinesis, in which the cytoplasm is

divided in two

Mitosis and CytokinesisMitosis and Cytokinesis

Mitosis consists of four distinct phases:• (A) Prophase• (B) Metaphase• (C) Anaphase• (D) Telophase

Cytokinesis typically:• Occurs during telophase• Divides the cytoplasm• Is different in plant and animal cells

Nuclearenvelope

LM

Plasmamembrane

Chromosome, consistingof two sister chromatids

Spindle microtubules

Fragments of nuclear envelopeCentrosome

Centromere

Early mitotic spindle

Centrosomes (with centriole pairs)

Chromatin

PROPHASEINTERPHASE

Figure 8.7.a

ProphaseProphase

• Chromosomes condense

• Nuclear membrane breaks down

• Centrioles migrate to opposite poles (in animal cells)

• Microtubules attach to chromosomes and centrioles

ProphaseProphase

ANAPHASEMETAPHASE TELOPHASE AND CYTOKINESIS

Spindle Daughterchromosomes

Cleavagefurrow

Nuclearenvelopeforming

Figure 8.7b

MetaphaseMetaphase

•Chromosomes line up along the center of the cell

MetaphaseMetaphase

AnaphaseAnaphase

•Microtubules shorten

•Chromatids separate a pull to opposite sides

AnaphaseAnaphase

TelophaseTelophase

•Nuclear membrane forms around each set of chromosomes

•Chromosomes unwind

CytokinesisCytokinesis

•Cytoplasm split in two

•Cell membrane separates the two daughter cells

Telophase and Cytokinesis

Telophase and Cytokinesis

Animal cell mitosisAnimal cell mitosis

Cleavagefurrow

SEM

Cleavage furrowContracting ring ofmicrofilaments

Daughter cellsFigure 8.8a

Plant Cell MitosisPlant Cell Mitosis

•Plant cell mitosis is similar to animal cell mitosis BUT cytokinesis is different• In plant, fungi and algae cell,

a cell plate forms in the middle of the cell to divide the two cells.

Daughter cells

New cell wallVesicles containingcell wall material Cell plateCell wall

Wall ofparent cell

Cell plateforming

Daughternucleus

LM

Figure 8.8b

Result of MitosisResult of Mitosis

• 2 daughter cells that are identical to each other and identical to the parent cell

Cancer Cells: Growing Out of ControlCancer Cells: Growing Out of Control

Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle.

What Is Cancer?What Is Cancer? Cancer is a disease of the cell cycle. Cancer cells do not respond normally to the cell cycle

control system. Cancer cells can form tumors, abnormally growing masses

of body cells. The spread of cancer cells beyond their original site of

origin is metastasis. Malignant tumors can:• Spread to other parts of the body• Interrupt normal body functions

Cancer TreatmentCancer Treatment

Cancer treatment can involve:• Radiation therapy, which damages DNA

and disrupts cell division• Chemotherapy, which uses drugs that

disrupt cell division

Cancer Prevention and Survival

Cancer Prevention and Survival

Certain behaviors can decrease the risk of cancer:• Not smoking• Exercising adequately• Avoiding exposure to the sun • Eating a high-fiber, low-fat diet• Performing self-exams• Regularly visiting a doctor to identify tumors

early

MeiosisMeiosis

Homologous ChromosomesHomologous Chromosomes

Different individuals of a single species have the same number and types of chromosomes.

A human somatic cell:• Is a typical body cell • Has 46 chromosomes

A karyotype is an image that reveals an orderly arrangement of chromosomes.

Homologous chromosomes are matching pairs of chromosomes that can possess different versions of the same genes.

Pair of homologouschromosomes

LM

One duplicatedchromosome

Centromere

Sisterchromatids

Figure 8.11

Human ChromosomesHuman Chromosomes

Humans have:• Two different sex chromosomes, X and Y• Twenty-two pairs of matching chromosomes,

called autosomes

Humans are diploid organisms in which:• Their somatic cells contain two sets of

chromosomes • Their gametes are haploid, having only one

set of chromosomes

Gametes and the Life Cycle of a Sexual Organism

Gametes and the Life Cycle of a Sexual Organism

The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next.

Multicellulardiploid adults(2n 46)

MEIOSIS FERTILIZATION

MITOSIS

2n

and development Key

Sperm cell

n

n

Diploidzygote(2n 46)

Diploid (2n)Haploid (n)

Egg cellHaploid gametes (n 23)

Figure 8.12

MeiosisMeiosis

Humans are diploid organisms in which:• Their somatic cells contain two sets of chromosomes • Their gametes are haploid, having only one set of

chromosomes

In humans, a haploid sperm fuses with a haploid egg during fertilization to form a diploid zygote.

Sexual life cycles involve an alternation of diploid and haploid stages.

Meiosis produces haploid gametes, which keeps the chromosome number from doubling every generation.

MEIOSIS I

Sisterchromatidsseparate.

MEIOSIS II

Homologouschromosomesseparate.

INTERPHASE BEFORE MEIOSIS

Sisterchromatids

Duplicated pair ofhomologouschromosomes

Chromosomesduplicate.

Pair of homologouschromosomes indiploid parent cell

Figure 8.13-3

The Process of MeiosisThe Process of Meiosis

In meiosis:• Haploid daughter cells are produced in diploid

organisms• Interphase is followed by two consecutive divisions,

meiosis I and meiosis II• Crossing over occurs

MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE

Sister chromatidsremain attached

Pair ofhomologouschromosomes

INTERPHASE

Sisterchromatids

Homologouschromosomespair up andexchangesegments.

Chromosomesduplicate.

Pairs of homologouschromosomesline up.

Pairs of homologouschromosomessplit up.

Nuclearenvelope

Chromatin

Centromere

Microtubulesattachedto chromosome

Sites of crossing over

Spindle

Centrosomes (with centriolepairs)

PROPHASE I METAPHASE I ANAPHASE I

Figure 8.14a

TELOPHASE II AND

CYTOKINESIS

Sister chromatidsseparate

ANAPHASE II

Cleavagefurrow

TELOPHASE I AND

CYTOKINESIS

Two haploidcells form;chromosomesare stilldoubled.

MEIOSIS II: SISTER CHROMATIDS SEPARATE

PROPHASE II METAPHASE II

During another round of cell division, the sisterchromatids finally separate; four haploid

daughter cells result, containing singlechromosomes.

Haploid daughtercells forming

Figure 8.14b

LM

Figure 8.14bc

Review: Comparing Mitosis and MeiosisReview: Comparing Mitosis and Meiosis

In mitosis and meiosis, the chromosomes duplicate only once, during the preceding interphase.

The number of cell divisions varies:• Mitosis uses one division and produces two

diploid cells• Meiosis uses two divisions and produces four

haploid cells All the events unique to meiosis occur during

meiosis I, while meiosis II is the same as mitosis since it separates sister chromatids.

Duplicated chromosome(two sister chromatids)

MITOSIS

Prophase

Chromosome duplication

Chromosomes align at the middle of thecell.

Metaphase

Sister chromatidsseparateduringanaphase.

AnaphaseTelophase

Daughter cellsof mitosis

2n2n

Prophase I

Metaphase I

Anaphase ITelophase I

MEIOSIS

Chromosome duplication

Homologous chromosomes come together in pairs.

MEIOSIS I

Site of crossing overbetween homologous(nonsister) chromatids

Homologous pairsalign at the middle of the cell.

Chromosome with twosister chromatids

Homologous chromosomes separate duringanaphase I;sister chromatidsremain together.

Daughtercells of meiosis I

Sister chromatidsseparate duringanaphase II.

Haploidn 2

MEIOSIS II

Parent cell(before chromosome duplication)

2n 4

Daughter cells of meiosis II n n n n

Figure 8.15

Independent Assortment of Chromosomes

Independent Assortment of Chromosomes When aligned during metaphase I of meiosis, the side-by-

side orientation of each homologous pair of chromosomes is a matter of chance.

Every chromosome pair orients independently of the others during meiosis.

For any species the total number of chromosome combinations that can appear in the gametes due to independent assortment is:• 2n where n is the haploid number.

For a human:• n = 23 • 223 = 8,388,608 different chromosome combinations possible

in a gamete

Metaphase ofmeiosis I

Metaphase of meiosis II

Combination a

POSSIBILITY 1 POSSIBILITY 2

Combination b Combination c Combination d

Gametes

Figure 8.16-3

Random FertilizationRandom Fertilization

A human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote.

If each gamete represents one of 8,388,608 different chromosome combinations, at fertilization, humans would have 8,388,608 × 8,388,608, or more than 70 trillion, different possible chromosome combinations.

Figure 8.17

Crossing OverCrossing Over

In crossing over:• Homologous chromosomes exchange

genetic information • Genetic recombination, the production of

gene combinations different from those carried by parental chromosomes, occurs

Metaphase I

Metaphase II

Recombinant chromosomes

Gametes Recombinant chromosomescombine geneticinformation fromdifferent parents.

Homologous chromatidsexchange correspondingsegments.

Sister chromatids remain joined at theircentromeres.

Prophase Iof meiosis

Duplicated pair ofhomologouschromosomes

Chiasma, site ofcrossing over

Spindlemicrotubule

Figure 8.18-5

How Accidents during Meiosis Can Alter Chromosome NumberHow Accidents during Meiosis

Can Alter Chromosome Number In nondisjunction, the members of a chromosome

pair fail to separate during anaphase, producing gametes with an incorrect number of chromosomes.

Nondisjunction can occur during meiosis I or II. If nondisjunction occurs, and a normal sperm

fertilizes an egg with an extra chromosome, the result is a zygote with a total of 2n + 1 chromosomes.

If the organism survives, it will have an abnormal number of genes.

Meiosis I

Abnormal gametes

Gametes

Nondisjunction:Pair of homologouschromosomes failsto separate.

NONDISJUNCTION IN MEIOSIS I

Number of chromosomes

Meiosis II

Nondisjunction:Pair of sisterchromatidsfails to separate.

Abnormal gametes Normal gametes

n n n 1n 1 n – 1n 1

NONDISJUNCTION IN MEIOSIS II

n – 1 n – 1

Figure 8.20-3

Abnormal eggcell with extrachromosome

Normalsperm cell

n 1

n (normal)

Abnormal zygotewith extrachromosome 2n 1

Figure 8.21

Down SyndromeDown Syndrome

Down Syndrome:• Is also called trisomy 21• Is a condition in which an individual has an

extra chromosome 21• Affects about one out of every 700 children• The incidence of Down Syndrome increases

with the age of the mother.

Chromosome 21

LM

Figure 8.22

Age of mother25 35 4520 30 40 50

10

0

20

30

40

50

60

70

80

90In

fant

s w

ith D

own

synd

rom

e(p

er 1

,000

birt

hs)

Figure 8.23

Abnormal Numbers of Sex Chromosomes

Abnormal Numbers of Sex Chromosomes

Nondisjunction can also affect the sex chromosomes.

Table 8.1

Evolution Connection:The Advantages of SexEvolution Connection:

The Advantages of Sex Asexual reproduction conveys an

evolutionary advantage when plants are:• Sparsely distributed • Superbly suited to a stable environment

Sexual reproduction may convey an evolutionary advantage by:• Speeding adaptation to a changing environment • Allowing a population to more easily rid itself of

harmful genes

Figure 8.24

Duplicationof all

chromosomes

Geneticallyidenticaldaughter

cells

Distribution viamitosis

Figure 8.UN1

Interphase Cell growth and

chromosome duplication

G2 Mitotic

(M) phase

S phase DNA synthesis; chromosome duplication

G1

Genetically identical“daughter”cells

Cytokinesis (division ofcytoplasm)

Mitosis (division ofnucleus)

Figure 8.UN3

MITOSIS

Male and femalediploid adults(2n 46)

MEIOSIS

Sperm cell

Human Life Cycle

KeyHaploid (n)

Diploid (2n)

Haploid gametes (n 23)

Egg cell

Diploid zygote(2n 46)

and development

FERTILIZATION

2n

n

n

Figure 8.UN4

Daughtercells

Parentcell (2n)

MITOSIS

Chromosomeduplication

2n 2n

MEIOSIS

MEIOSIS I Parentcell (2n)

Chromosomeduplication

Daughter cellsn

MEIOSIS II

Pairing of homologouschromosome

Crossing over

n nn

Figure 8.UN5

Differences between Mitosis and Meiosis

Differences between Mitosis and Meiosis

• Meiosis has 2 divisions – two rounds of chromosome separation.

• Crossing over in meiosis – exchange of genetic material between homologous chromosomes – occurs during synapsis(pairing of homologous chromosomes in M I)

Differences between Mitosis and Meiosis

Differences between Mitosis and Meiosis

• Mitosis occurs in all cells, meiosis limited to certain cells• Mitosis produces 2 identical cells, Meiosis

produce 4 cells which are not identical• Mitosis : daughter cells of same ploidy as

parent; Meiosis: daughter cells haploid of parent

(a)

LM

(b)

(c)

(d)

Figure 8.UN6