08 lecture presentation

Copyright © 2009 Pearson Education, Inc.

Chapter 8Chapter 8 The Cellular Basis of Reproduction and Inheritance

CONNECTIONS BETWEEN CELL DIVISION AND

REPRODUCTION


8.1 Like begets like, more or less

• Living organisms reproduce by 2 methods

1. Asexual reproduction

• Offspring are identical to the original cell or organism

• Involves inheritance of all genes from one parent

2. Sexual reproduction

• Offspring are similar to parents, but show variations in traits

• Involves inheritance of unique sets of genes from two parents


• Cell division perpetuates life

– Cell division is the reproduction of cells

– Virchow’s principle states “Every cell from a cell”

– Perpetuation of life depends on cell division

8.2 Cells arise only from preexisting cells


– Roles of cell division

– Asexual reproduction

– Reproduction of an entire single-celled organism

– Growth of a multicellular organism

– Growth from a fertilized egg into an adult

– Repair and replacement of cells in an adult

– Sexual reproduction

– Sperm and egg production

8.2 Cells arise only from preexisting cells


• Binary fission means “dividing in half”

– Asexual reproduction, occurs in prokaryotic cells

– 2 identical cells arise from 1 cell

– Steps in the process:

1. A single circular chromosome duplicates, and the copies begin to separate from each other

2. The cell elongates, and the chromosomal copies separate further

3. The plasma membrane grows inward at the midpoint to divide the cells

8.3 Prokaryotes reproduce by binary fission


Prokaryoticchromosome

Duplication of chromosomeand separation of copies

Cell wall

Plasmamembrane

1



Cell wall

Plasmamembrane

1

Continued elongation of thecell and movement of copies

2



Cell wall

Plasmamembrane

1

Continued elongation of thecell and movement of copies

2

Division intotwo daughter cells

3

Prokaryotic chromosomes

Binary fission of a dividing bacterium

THE EUKARYOTIC CELL CYCLE AND MITOSIS


• Eukaryotic chromosomes are composed of chromatin

– Chromatin = DNA + proteins

– To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope

– Early in the division process, chromosomes duplicate

– Each chromosome appears as 2 sister chromatids, containing identical DNA molecules

– Sister chromatids are joined at the centromere, a narrow region

8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division


Plant cell just before division

Sister chromatids

Centromere Centromere

Chromosomeduplication

Sister chromatids

Chromosomedistribution

todaughter

cells

• The cell cycle is an ordered sequence of events for cell division

• It consists of 2 major stages:

1. Interphase: duplication of cell contents

1. G1— (gap 1) cell growth, increase in cytoplasm

2. S— (synthesis) duplication of chromosomes/DNA

3. G2— (gap 2) cell growth, preparation for division

2. Mitotic phase (M Phase): cell division

1. Mitosis—division of the nucleus

2. Cytokinesis—division of cytoplasm

8.5 The cell cycle multiplies cells


S(DNA synthesis)G1

G2

Cytokinesis

Mito

sis

INTERPHASE

MITOTICPHASE (M)

• Mitosis progresses through a series of stages:

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

• Cytokinesis often overlaps telophase

8.6 Cell division is a continuum of dynamic changes


• A mitotic spindle is required to divide the chromosomes

– The mitotic spindle is composed of microtubules

– Mitotic spindle is produced by centrosomes

– Organize microtubule arrangement

– Contain a pair of centrioles in animal cells



Centrosomes(with centriole pairs) Kinetochore

Early mitoticspindle

Chromatin

INTERPHASE PROMETAPHASEPROPHASE

Centrosome Fragmentsof nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Nuclearenvelope

Spindlemicrotubules

Nucleolus

Centromere

Interphase

– In the cytoplasm

– Cytoplasmic contents double

– 2 centrosomes form

– In the nucleus

– Chromosomes duplicate during the S phase

– Nucleolus is visible

INTERPHASE

– Applying Your Knowledge:Human cells have 46 chromosomes (23 pairs). By the end of interphase

– How many chromosomes are present in one cell?

– 46 duplicated chromosomes

– How many chromatids are present in one cell?

– 92 chromatids



KinetochoreEarly mitoticspindle

PROMETAPHASEPROPHASE



Spindlemicrotubules

Centromere

1. Prophase

– In the cytoplasm

– Spindle fibers (microtubules) begin to emerge from centrosomes

– In the nucleus

– Chromosomes condense and shorten

– Nucleolus disappears

– Nuclear envelope breaks down

PROPHASE

Kinetochore

PROMETAPHASE

Fragmentsof nuclearenvelope

Spindlemicrotubules

2. Prometaphase

– Spindle fibers attach at kinetochores on the centromeres of sister chromatids

– Move chromosomes to the center of the cell through associated protein “motors”

– Other microtubules meet those from the opposite poles

– The nuclear envelope disappears

PROMETAPHASE

Centrosomes(with centriole pairs) Kinetochore

Early mitoticspindle

Chromatin

INTERPHASE PROMETAPHASEPROPHASE


Plasmamembrane


Nuclearenvelope

Spindlemicrotubules

Nucleolus

Centromere

Metaphaseplate

METAPHASE TELOPHASE AND CYTOKINESIS

DaughterchromosomesSpindle

3. Metaphase

– Spindle is fully formed

– Chromosomes align at the cell equator

– Kinetochores of sister chromatids are facing the opposite poles of the spindle

METAPHASE

TELOPHASE AND CYTOKINESISANAPHASE

Daughterchromosomes

4. Anaphase

– Sister chromatids separate and move to opposite poles of the cell

– Daughter chromosomes break apart

– The cell elongates due to lengthening of microtubules

ANAPHASE

Nucleolusforming

TELOPHASE AND CYTOKINESIS

Cleavagefurrow

Nuclearenvelopeforming

5. Telophase– Cell continues to elongate

– Nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei

– Chromatin uncoils

– Nucleoli reappear

– Spindle disappears

– By the end of telophase – How many chromosomes are

present in one nucleus within the human cell?

– 46 single chromosomes

– Are the nuclei identical or different?

– identical

TELOPHASE AND CYTOKINESIS

Metaphaseplate

Nucleolusforming

METAPHASE TELOPHASE AND CYTOKINESISANAPHASE

Cleavagefurrow

Daughterchromosomes

NuclearenvelopeformingSpindle

• Cytokinesis – cytoplasm is divided into separate cells

– Cleavage in animal cells – A cleavage furrow forms from a contracting ring of

microfilaments, interacting with myosin

– The cleavage furrow deepens to separate the contents into two cells

– Cytokinesis in plant cells– A cell plate forms in the middle from vesicles

containing cell wall material

– The cell plate grows outward to reach the edges, dividing the contents into two cells

– Each cell has a plasma membrane and cell wall

8.7 Cytokinesis differs for plant and animal cells


Cleavagefurrow

Contracting ring ofmicrofilaments

Daughter cells

Cleavage furrow

Cell plate Daughter cells

Cell wall

Vesicles containingcell wall material

Daughter nucleus

Cell plateforming

Wall ofparent cell

New cell wall

• Skip this section

8.8 Anchorage, cell density, and chemical growthfactors affect cell division


• A set of molecules, including growth factors, that triggers and coordinates events of the cell cycle

• Checkpoints = Control points where intercellular signals detected by the control system tell it whether key cellular processes up to each point have been completed

1. G1 checkpoint allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G0 phase

2. G2 checkpoint

3. M checkpoint

8.9 Growth factors signal the cell cycle control system

G1 checkpoint

Controlsystem

M

S

G2

G1

M checkpoint

G2 checkpoint

G0

• Effects of a growth factor at the G1 checkpoint

– A growth factor binds to a receptor in the plasma membrane

– A signal transduction pathway propagates the signal through a series of relay molecules

– The signal reaches the cell cycle control system to trigger entry into the S phase

8.9 Growth factors signal the cell cycle control system


G1 checkpoint

Controlsystem

M

S

G2

G1

Receptorprotein

Signaltransductionpathway

Relayproteins

Plasma membrane

Growth factor

• Cancer cells escape controls on the cell cycle

– Cancer cells divide rapidly, often in the absence of growth factors

– They spread to other tissues through the circulatory system

– Growth is not inhibited by other cells, and tumors form

– Benign tumors remain at the original site

– Malignant tumors spread to other locations by metastasis

8.10 CONNECTION: Growing out of control, cancer cells produce malignant tumors


• Cancer treatments

– Localized tumors can be treated with surgery or radiation

– Chemotherapy is used for metastatic tumors

8.10 CONNECTION: Growing out of control, cancer cells produce malignant tumors


A tumor grows from asingle cancer cell.

Cancer cells spreadthrough lymph andblood vessels toother parts of the body.

Cancer cells invadeneighboring tissue.

Tumor

Glandulartissue

Lymphvessels

Bloodvessel

• Mitosis produces genetically identical cells for

– Growth

– Replacement

– Asexual reproduction

8.11 Review: Mitosis provides for growth, cell replacement, and asexual reproduction


MEIOSIS AND CROSSING OVER


• Somatic cells (typical body cells) have pairs of homologous chromosomes

• Homologous chromosomes are matched in

1. Length

2. Centromere position

3. Gene locations

– Locus (plural, loci) is the position of a gene

– Different versions of a gene may be found at the same locus on maternal and paternal chromosomes

8.12 Chromosomes are matched in homologous pairs


• We inherit one chromosome of each homologous pair from our mother and one from our father

• The human sex chromosomes X and Y differ in size and genetic composition

• Pairs of autosomes have the same size and genetic composition

– Humans have 46 chromosomes or 23 homologous pairs

– There are 2 sex chromosomes that differ in size and composition, however they act like a homologous pair

– Thus, 22 pairs of chromosomes are autosomes

8.12 Chromosomes are matched in homologous pairs


Sister chromatids One duplicatedchromosome

Centromere

Homologous pair ofchromosomes

• Meiosis is a process that converts diploid nuclei to haploid nuclei

– Diploid cells have two homologous sets of chromosomes (2n = 46)

– Haploid cells have one set of chromosomes (n = 23)

– Meiosis occurs in the sex organs, producing gametes—sperm and eggs

• Fertilization is the union of sperm and egg

– The zygote has a diploid chromosome number, one set from each parent

8.13 Gametes have a single set of chromosomes


Haploid gametes (n = 23)

nnEgg cell

Sperm cellFertilizationMeiosis

Multicellulardiploid adults

(2n = 46)

Mitosis anddevelopment

nn

22nn

Diploidzygote

(2n = 46)

• Like mitosis, meiosis is preceded by interphase

– Chromosomes duplicate during the S phase

• Unlike mitosis, meiosis has two divisions

– During meiosis I, homologous chromosomes separate

– The chromosome number is reduced by half

– During meiosis II, sister chromatids separate

– The chromosome number remains the same

8.14 Meiosis reduces the chromosome number from diploid to haploid


2 Types of Cell Division in Eukaryotes: Mitosis & Meiosis

Mitosis

Cell replication

Produces 2 diploid daughter cells

Daughter cells get one copy of the parent cell’s replicated chromosome

Meiosis

Prerequisite for sexual reproduction

Specialized nuclear division & 2 rounds of cytokinesis

Produces 4 haploid daughter cells (gametes)

Gametes carry ½ the genetic material of the parent

How does meiosis make haploid cells?

Meiosis undergoes 1 round of DNA replication followed by 2 rounds of division

One round of DNA replication creates 4 chromatids for each type of chromosome

• Events in Meiosis:

1. Prophase I

2. Metaphase I

3. Anaphase I

4. Telophase I and Cytokinesis

5. Prophase II

6. Metaphase II

7. Anaphase II

8. Telophase II and Cytokinesis



Meiosis IHomologous chromosomes separate

Meiosis IISister chromatids separate

• Prophase I

– Chromosomes coil and become compact

– Homologous chromosomes come together as pairs by synapsis

– Each pair, with four chromatids, is called a tetrad

– Nonsister chromatids exchange genetic material by crossing over



• Metaphase I

– Tetrads align at the cell equator

– One homologue of each pair faces each pole of the cell & attaches to spindle fibers at kinetochore

• Anaphase I

– Homologous pairs separate and move toward opposite poles of the cell

– Sister chromatids do not separate



• Telophase I

– Duplicated chromosomes have reached the poles

– Nuclear envelope forms around chromosomes

– Each nucleus has the haploid number of chromosomes

• Cytokinesis

• END OF MEIOSIS I

• After telophase I and cytokinesis:

• 2 daughter cells each with 23 duplicated chromosomes



Centrosomes(with centriolepairs)

PROPHASE I

Microtubulesattached tokinetochore

INTERPHASE

Sites of crossing over Metaphaseplate

Spindle

MEIOSIS I: Homologous chromosomes separate

METAPHASE I

Sister chromatidsremain attached

ANAPHASE I

Nuclearenvelope

Sisterchromatids

Centromere(with kinetochore)

Homologouschromosomes separateChromatin

Tetrad

Cleavagefurrow

TELOPHASE IIAND CYTOKINESIS

• Meiosis II follows meiosis I without chromosome duplication and little to no Interphase

• Each of the two haploid daughter cells enters meiosis II



• Prophase II

– Chromosomes coil and become compact

– Spindle fibers re-form & attach to sister chromatids



• Metaphase II

– Duplicated chromosomes align at the cell equator

– sister chromatids of each chromosome attached to spindle fibers that lead to opposite poles

• Anaphase II

– Sister chromatids separate and independent daughter chromosomes move toward opposite poles



• Telophase II

– Chromosomes have reached the poles of the cell

– A nuclear envelope forms around each set of chromosomes

• Cytokinesis

• END OF MEIOSIS II

• After telophase II and cytokinesis: • 4 cells with 23 daughter chromosomes in each cell (haploid)



PROPHASE I

MEIOSIS II: Sister chromatids separate

METAPHASE II ANAPHASE II

Cleavagefurrow


Sister chromatidsseparate

Haploid daughtercells forming


• Which characteristics are similar for mitosis and meiosis?

– One duplication of chromosomes

• Which characteristics are unique to meiosis?

– Two divisions of chromosomes

– Pairing of homologous chromosomes

– Exchange of genetic material by crossing over

8.15 Mitosis and meiosis have important similarities and differences


• What is the outcome of each process?

– Mitosis: two genetically identical cells, with the same chromosome number as the original cell

– Meiosis: four genetically different cells, with half the chromosome number of the original cell

8.15 Mitosis and meiosis have important similarities and differences


Prophase

Metaphase IMetaphase

2n = 4

Tetradsalign at themetaphase plate

Duplicatedchromosome(two sisterchromatids)

Parent cell(before chromosome duplication)


Chromosomesalign at themetaphase plate

AnaphaseTelophase Sister chromatids

separate duringanaphase

Daughter cellsof mitosis

2n 2n

n


Site ofcrossing over

Tetrad formedby synapsis ofhomologouschromosomes

MEIOSIS

Prophase I

Anaphase ITelophase I

MITOSIS

MEIOSIS I

Haploidn = 2

Daughtercells of

meiosis I

MEIOSIS II

n n n

Daughter cells of meiosis II

Homologouschromosomesseparate(anaphase I);sister chroma-tids remaintogether

No furtherchromosomalduplication;sisterchromatidsseparate(anaphase II)

• Independent orientation at metaphase I– Each pair of chromosomes independently

aligns at the cell equator– There is an equal probability of the maternal

or paternal chromosome facing a given pole– The number of combinations for chromosomes

packaged into gametes is 2n where n = haploid number of chromosomes

8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring


Two equally probablearrangements ofchromosomes at

metaphase I

Possibility 1 Possibility 2


metaphase I


Metaphase II


metaphase I


Metaphase II

Combination 1

Gametes

Combination 2 Combination 3 Combination 4

• Random fertilization– The combination of each unique sperm with

each unique egg increases genetic variability

8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring


8.17 Homologous chromosomes can carry different versions of genes

• SKIP

• Genetic recombination is the production of new combinations of genes due to crossing over

• Crossing over involves exchange of genetic material between homologous chromosomes during Prophase I

– Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over

– Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids

8.18 Crossing over further increases genetic variability


Centromere

ChiasmaTetrad

Breakage of homologous chromatids

Coat-colorgenes

Eye-colorgenes

C

(homologous pair ofchromosomes in synapsis)

E

c e

Tetrad

C E

c e

Joining of homologous chromatids2

C E

c e

Chiasma

1

Separation of homologous chromosomes at anaphase I

C E

c e

Chiasma

Separation of chromatids at anaphase II andcompletion of meiosis

C E

c e

c E

C e

c e

c E

C E

C e

Parental type of chromosome

Gametes of four genetic types

Recombinant chromosome

Parental type of chromosome

Recombinant chromosome

4

3

ALTERATIONS OF CHROMOSOME NUMBER AND

STRUCTURE


• A karyotype shows stained and magnified versions of chromosomes

– Karyotypes are produced from dividing white blood cells, stopped at metaphase

– Karyotypes allow observation of :

– Homologous chromosome pairs

– Chromosome number

– Chromosome structure

8.19 A karyotype is a photographic inventory of an individual’s chromosomes


Packed redand white bloodcells

CentrifugeBloodculture

Fluid1

Blood culture is centrifuged to separate the blood cellsFrom the culture fluid



Fluid1

Hypotonicsolution

2

Fluid is discarded, and a hypotonic solution is mixed with The cells. This makes the RBC burst, the WBC swell but

Do not burst, and their chromosomes spread out



Fluid1

Hypotonicsolution

2

3

Fixative

Whitebloodcells

Stain

Another centrifugation separates the WBC. The fluidContaining the remnants of RBCs is discarded. A preservative

Is mixed w/ the WBC and a drop of the cell suspension isSpread on a microscope slide, dried, and stained.

Centromere

Sisterchromatids

Pair of homologouschromosomes

5

Digital photograph of chromosomes is obtained and a computer Sorts them by size and shape. Resulting karyotype is below.

22 pairs of autosomes, 2 sex chromosomes

• Trisomy 21 involves the inheritance of three copies of chromosome 21

– Trisomy 21 is the most common human chromosome abnormality

– An imbalance in chromosome number causes Down syndrome, which is characterized by

– Characteristic facial features

– Susceptibility to disease

– Shortened life span

– Mental retardation

– Variation in characteristics

– The incidence increases with the age of the mother

8.20 CONNECTION: An extra copy of chromosome 21 causes Down syndrome


Infa

nts

wit

h D

ow

n s

ynd

rom

e(p

er 1

,000

bir

ths)

Age of mother

90

70

60

50

40

30

20

10

0

80

20 40353025 5045

• Nondisjunction is the failure of chromosomes or chromatids to separate during meiosis

– During Meiosis I

– Both members of a homologous pair go to one pole

– During Meiosis II

– Both sister chromatids go to one pole

• Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes

• Ex: Downs Syndrome (trisomy 21) results from nondisjunction

8.21 Accidents during meiosis can alter chromosome number


Nondisjunctionin meiosis I


Normalmeiosis II


Normalmeiosis II

n + 1

Gametes

Number of chromosomes

n + 1 n – 1 n – 1

Normalmeiosis I

Nondisjunctionin meiosis II

Normalmeiosis I

Nondisjunctionin meiosis II

Normalmeiosis I

Gametes

Number of chromosomes

n + 1 n – 1 n n

• Sex chromosome abnormalities tend to be less severe as a result of

– Small size of the Y chromosome

– X-chromosome inactivation

– In each cell of a human female, one of the two X chromosomes becomes tightly coiled and inactive

– This is a random process that inactivates either the maternal or paternal chromosome

– Inactivation promotes a balance between the number of X chromosomes and autosomes

8.22 CONNECTION: Abnormal numbers of sexchromosomes do not usually affect survival


• Polyploid species have more than two chromosome sets

– Observed in many plant species

– Seen less frequently in animals

• Example:

– Diploid gametes are produced by failures in meiosis

– Diploid gamete + Diploid gamete Tetraploid offspring

– The tetraploid offspring have four chromosome sets

8.23 EVOLUTION CONNECTION: New species

can arise from errors in cell division


• Structure changes result from breakage and rejoining of chromosome segments

• Know the following for the test:– Deletion is the loss of a chromosome segment– Duplication is the repeat of a chromosome

segment – Inversion is the reversal of a chromosome

segment– Translocation is the attachment of a segment to

a nonhomologous chromosome; can be reciprocal

• Altered chromosomes carried by gametes cause birth defects

• Chromosomal alterations in somatic cells can cause cancer

8.24 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer


Deletion

Inversion

Duplication

Homologouschromosomes

Reciprocaltranslocation

Nonhomologouschromosomes

Chromosome 9

“Philadelphia chromosome”

Activated cancer-causing gene

Reciprocaltranslocation

Chromosome 22

Need Chemistry Help?Need Chemistry Help?

ContactContact Veronica WalkerVeronica Walker

for FREE tutoring! for FREE tutoring!

[email protected]@gsc.edu

Need Biology Need Biology Help??Help??

ContactContact Veronica WalkerVeronica Walker

for FREE tutoring! for FREE tutoring!

[email protected]@gsc.edu

08 lecture presentation

Education

Transcript of 08 lecture presentation