Ch. 8 The Cellular Basis of Reproduction and Inheritance © 2012 Pearson Education, Inc.

Ch. 8 The Cellular Basis of Reproduction and Inheritance

© 2012 Pearson Education, Inc.

Cell division plays many important roles in the lives of organisms

Living organisms reproduce by two methods.

– Asexual reproduction

– offspring are identical to the parent

– involves inheritance of all genes from one parent.

– Sexual reproduction

– offspring are similar to the parents, but show variations in traits

– involves inheritance of unique sets of genes from two parents.


Cell division is reproduction at the cellular level,

Requires duplication of chromosomes, sorting new sets of chromosomes into the resulting pair of daughter cells.


Cell division is used for:

– Reproduction of single-celled organisms

– Growth of multicellular organisms from a fertilized egg into an adult,

– Repair and replacement of cells

– Sperm and egg production.



Prokaryotes (bacteria and archaea) reproduce by binary fission “dividing in half”

Binary Fission Occurs in Three Steps:

1. duplication of the chromosome and separation of the copies,

2. continued elongation of the cell and movement of the copies

3. division into two daughter cells.

The chromosome of a prokaryote is:

A singular circular DNA molecule & associated proteins

Much smaller than eukaryotic DNA

Prokaryotes reproduce by binary fission


Figure 8.2A_s3

Plasmamembrane

Cell wall

Duplication of the chromosomeand separation of the copies

Continued elongation of thecell and movement of the copies

Prokaryoticchromosome

1

2

3Division into

two daughter cells

THE EUKARYOTIC CELL CYCLE AND MITOSIS


Eukaryotic cells have more genes, and store most of their genes on multiple chromosomes within the nucleus.

Eukaryotic chromosomes are composed of chromatin = one long DNA molecule and proteins

Before dividing chromatin becomes highly compact (into chromosomes) and visible with a microscope

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


Figure 8.3B

Sisterchromatids

Chromosomes

Centromere

Chromosomeduplication

Sisterchromatids

Chromosomedistribution

to thedaughter

cells

DNA molecules

Before a eukaryotic cell divides, it duplicates all of its chromosomes, resulting in two copies called sister chromatids joined together by a narrowed “waist” called the centromere.

When a cell divides, the sister chromatids separate from each other, (now called chromosomes) and sort into separate daughter cells.

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


Figure 8.3B_1Chromosomes

Centromere


Sisterchromatids

Chromosomedistribution

to thedaughter

cells

DNA molecules

The cell cycle extends from the time a cell is first formed until its own division.

The cell cycle multiplies cells


The cell cycle consists of two stages, characterized as follows:

1. Interphase:

G1—growth, increase in cytoplasm

– S—duplication of chromosomes

– G2—growth, preparation for division

1. Mitotic phase: nuclear division

– Mitosis—division of the chromosomes in nucleus

– Cytokinesis—division of cytoplasm

The cell cycle multiplies cells


G1

(first gap)S

(DNA synthesis)

G2

(second gap)

M

CytokinesisM

itosi

s

I N T E R P H A S E

PHASE

TT

MI

OIC

Mitosis progresses through a series of stages (nuclear division):

– prophase

– prometaphase

– metaphase

– anaphase

– telophase.

Cytokinesis often overlaps telophase.

Cell division is a continuum of dynamic changes


INTERPHASEMITOSIS

Prophase Prometaphase

Centrosome

Early mitoticspindle

Chromatin

Fragments ofthe nuclearenvelope

Kinetochore

Centrosomes(with centriole pairs)

Centrioles

Nuclearenvelope

Plasmamembrane

Chromosome,consisting of twosister chromatids

CentromereSpindlemicrotubules

Prophase

– In the cytoplasm microtubules begin to emerge from centrosomes, forming the mitotic spindle.

– In the nucleus chromosomes coil and become compact and visible with a light microscope

– Nucleoli disappear.



Prometaphase

– Spindle microtubules attach at kinetochores on centromeres of sister chromatids and move chromosomes to the center of the cell

– The nuclear envelope disappears.



MITOSIS

AnaphaseMetaphase Telophase and Cytokinesis

Metaphaseplate Cleavage

furrow

NuclearenvelopeformingDaughter

chromosomesMitoticspindle

Metaphase

– The mitotic spindle is fully formed and chromosomes align at the cell equator.

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



Anaphase – Sister chromatids separate

at centromeres and daughter chromosomes are moved to opposite poles of the cell

– The cell elongates due to lengthening of nonkinetochore microtubules.



Telophase– The cell continues to elongate

and nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei

– Chromatin uncoils and nucleoli reappear.

– The spindle disappears.



Cytokinesis differs in animal and plant cells.

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

Cell wallof theparent cell

Daughternucleus

Cell wall

Plasmamembrane

Vesiclescontainingcell wallmaterial

Cell plateforming

Newcell wall

Cell plate Daughtercells

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

with a plasma membrane and cell wall.

Anchorage, cell density, and chemical growthfactors affect cell division


Cell division is controlled by

– presence of nutrients

– density-dependent inhibition

– anchorage dependence

– growth factors

The addition ofgrowthfactor

Receptorprotein

Signaltransductionpathway

Growthfactor

Relay proteins

Plasma membrane EXTRACELLULAR FLUID

CYTOPLASM

G1

checkpoint

G1S

M

G2

Controlsystem

Tumor

Glandulartissue

Cancer cells invade neighboring tissue

Metastasis

Tumor cells can spread through lymph

and blood vessels

Cancer cells escape controls on the cell cycle.

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

Cancer Treatment

Radiaiton

Proton Therapy

Chemotherapy


MEIOSIS AND CROSSING OVER


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

– Diploid cells have two sets of chromosomes.

– Haploid cells have one set of chromosomes.

Meiosis occurs in 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.

Gametes have a single set of chromosomes


Haploid gametes (n 23)

Egg cell

Sperm cell

Fertilization

n

n

Meiosis

Ovary Testis

Diploidzygote(2n 46)

2n

MitosisKey

Haploid stage (n)Diploid stage (2n)

Multicellular diploidadults (2n 46)

In humans, body (somatic) cells have 23 pairs of homologous chromosomes: One member of each is from each parent.

One pair = sex chromosomes = X and Y

The other 22 pairs of chromosomes are autosomes;

Chromosomes are matched in homologous pairs

Chromosomes are matched in homologous pairs


Homologous chromosomes are matched in length, centromere position, and gene locations (except X & Y)

A locus is the position of a gene.

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

Locus

Pair of homologouschromosomes

One duplicatedchromosomeSister

chromatids

A pair ofhomologouschromosomesin a diploidparent cell

A pair ofduplicatedhomologouschromosomes

Sisterchromatids

1 2 3

INTERPHASE MEIOSIS I MEIOSIS II

Meiosis I – Prophase I

– Chromatin condensation

– Homologous chromosomes come together

– The homologous pairs, now form a tetrad.

– Nonsister chromatids exchange genetic material by crossing over at the chiasma

Meiosis reduces the chromosome number from diploid to haploid


Centrosomes(with centriolepairs) Centrioles

Sites of crossing over

Spindle

Tetrad

Nuclearenvelope

Chromatin Sisterchromatids Fragments

of thenuclearenvelope

Chromosomes duplicate Prophase IINTERPHASE:

MEIOSIS I

Meiosis I – Metaphase I – Tetrads align at the cell equator.

Meiosis I – Anaphase I – Homologous pairs separate and move toward opposite poles of the cell.



Centromere(with akinetochore)

Spindle microtubulesattached to a kinetochore

Metaphaseplate Homologous

chromosomesseparate

Sister chromatidsremain attached

Metaphase I Anaphase I

MEIOSIS I

Meiosis I – Telophase I –duplicated chromosomes have reached the poles, nuclear envelope re-forms around chromosomes, each nucleus has the haploid number of chromosomes.



Meiosis II follows meiosis I without chromosome duplication.

Each of the two haploid products enters meiosis II.

Meiosis II – Prophase II

– Chromosomes condense (if uncoiled).

– If re-formed nuclear envelope breaks up again.



Meiosis II – Metaphase II – Duplicated chromosomes align at equator.

Meiosis II – Anaphase II sister chromatids separate, move towards opposite pole.

Meiosis II – Telophase II - four haploid cells are produced



Figure 8.13_right

Cleavagefurrow

Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II

MEIOSIS II: Sister chromatids separate

Sister chromatidsseparate

Haploid daughtercells forming

Telophase IIand Cytokinesis

Mitosis and meiosis both

– begin with diploid parent cells

– have chromosomes duplicated during interphase.

However the end products differ.

– Mitosis produces two genetically identical diploid somatic daughter cells.

– Meiosis produces four genetically unique haploid gametes.

Mitosis and meiosis have important similarities and differences


Figure 8.14

Prophase

Metaphase

Duplicatedchromosome(two sisterchromatids)

MITOSIS

Parent cell(before chromosome duplication)



Site ofcrossingover

2n 4

Chromosomesalign at themetaphase plate

Tetrads (homologouspairs) align at themetaphase plate

Tetrad formedby synapsis ofhomologouschromosomes

Metaphase I

Prophase I

MEIOSIS I

AnaphaseTelophase

Sister chromatidsseparate during

anaphase

2n 2n

Daughter cells of mitosis

No furtherchromosomalduplication;sisterchromatidsseparate duringanaphase II

n n n n

Daughter cells of meiosis II

Daughtercells of

meiosis I

Haploidn 2

Anaphase ITelophase I

Homologouschromosomesseparate duringanaphase I;sisterchromatidsremain together

MEIOSIS II

Possibility A

Two equally probablearrangements ofchromosomes at

metaphase I

Possibility B

Metaphase II

Gametes

Combination 3 Combination 4Combination 2Combination 1

A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs.

Karyotypes

– are often produced from dividing cells arrested at metaphase of mitosis and

– allow for the observation of

– homologous chromosome pairs,

– chromosome number, and

– chromosome structure.

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


Bloodculture

Packed redand whiteblood cells

Centrifuge

Fluid

Hypotonicsolution Fixative

Whitebloodcells

Stain

3

2

1

Trisomy 21

Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen during

– meiosis I, if both members of a homologous pair go to one pole or

– meiosis II if both sister chromatids go to one pole.

Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes.

Accidents during meiosis can alter chromosome number


Figure 8.20A_s3

Nondisjunction

Normalmeiosis II

Gametes

# ofchromosomes

n 1 n 1 n 1 n 1

Nondisjunction

MEIOSIS II

MEIOSIS I

n 1 n 1 nn

Chromosome breakage can lead to rearrangements that can produce

– genetic disorders or, if changes occur in somatic cells, cancer.

These rearrangements may include

– a deletion, the loss of a chromosome segment,

– a duplication, the repeat of a chromosome segment,

– an inversion, the reversal of a chromosome segment, or

– a translocation, the attachment of a segment to a nonhomologous chromosome that can be reciprocal

Alterations of chromosome structure can cause birth defects and cancer

Deletion

Duplication

Inversion

Reciprocal translocation

Homologouschromosomes Nonhomologous

chromosomes

Chronic myelogenous leukemia (CML)

– is one of the most common leukemias

– affects cells that give rise to white blood cells (leukocytes)

– results from part of chromosome 22 switching places with a small fragment from a tip of chromosome 9.

Alterations of chromosome structure can cause birth defects and cancer


Chromosome 9

Chromosome 22

“Philadelphia chromosome”

Number of chromosomalduplications

Number of cell divisions

Number of daughter cellsproduced

Number of chromosomes inthe daughter cells

How the chromosomes lineup during metaphase

Genetic relationship of thedaughter cells to the parent cell

Functions performed in thehuman body

Mitosis Meiosis

Ch. 8 The Cellular Basis of Reproduction and Inheritance © 2012 Pearson Education, Inc.

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Transcript of Ch. 8 The Cellular Basis of Reproduction and Inheritance © 2012 Pearson Education, Inc.