CHAPTER 8 The Cellular Basis of Reproduction and Inheritance

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 8The Cellular Basis of

Reproduction and Inheritance

Modules 8.1 – 8.3


• The life cycle of a multicellular organism includes

– development

– reproduction

• This sea star embryo (morula) shows one stage in the development of a fertilized egg

– The cluster of cells will continue to divide as development proceeds

How to Make a Sea Star — With and Without Sex


• Some organisms can also reproduce asexually– This sea star is regenerating a lost arm

– Regeneration results from repeated cell divisions


• Cell division is at the heart of the reproduction of cells and organisms

• Organisms can reproduce sexually or asexually

CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION


• Some organisms make exact copies of themselves, asexual reproduction

8.1 Like begets like, more or less

Figure 8.1A


• Other organisms make similar copies of themselves in a more complex process, sexual reproduction

Figure 8.1B


• All cells come from cells

• Cellular reproduction is called cell division

– Cell division allows an embryo to develop into an adult

– It also ensures the continuity of life from one generation to the next

8.2 Cells arise only from preexisting cells


• Prokaryotic cells divide asexually

– These cells possess a single chromosome, containing genes

– The chromosome is replicated

– The cell then divides into two cells, a process called binary fission

8.3 Prokaryotes reproduce by binary fission

Figure 8.3B

Prokaryotic chromosomes


Figure 8.3A

• Binary fission of a prokaryotic cell

Prokaryoticchromosome

Plasmamembrane

Cell wall

Duplication of chromosomeand separation of copies

Continued growth of the cell and movement of copies

Division intotwo cells


Fourth Edition






Modules 8.4 – 8.11


• A eukaryotic cell has many more genes than a prokaryotic cell

– The genes are grouped into multiple chromosomes, found in the nucleus

– The chromosomes of this plant cell are stained dark purple

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

THE EUKARYOTIC CELL CYCLE AND MITOSIS

Figure 8.4A


• Chromosomes contain a very long DNA molecule with thousands of genes

– Individual chromosomes are only visibleduring cell division

– They are packaged as chromatin


• Before a cell starts dividing, the chromosomes are duplicated

– This process produces sister chromatids

Centromere

Sister chromatids

Figure 8.4B


• When the cell divides, the sister chromatids separate – Two daughter

cells are produced

– Each has a complete and identical set of chromosomes

Centromere Sister chromatids

Figure 8.4C

Chromosomeduplication

Chromosomedistribution

todaughter

cells


• The cell cycle consists of two major phases:

– Interphase, where chromosomes duplicate

and cell parts are made

– The mitotic phase, when cell division occurs

8.5 The cell cycle multiplies cells

Figure 8.5


• Eukaryotic cell division consists of two stages:

– Mitosis

– Cytokinesis

8.6 Cell division is a continuum of dynamic changes


• In mitosis, the duplicated chromosomes are distributed into two daughter nuclei

– After the chromosomes coil up, a mitotic spindle moves them to the middle of the cell


INTERPHASE PROPHASE

Centrosomes(with centriole pairs)

Chromatin

Nucleolus Nuclearenvelope

Plasmamembrane

Early mitoticspindle

Centrosome

CentrosomeChromosome,consisting of twosister chromatids

Fragmentsof nuclearenvelope

Kinetochore

Spindlemicrotubules

Figure 8.6


• The sister chromatids then separate and move to opposite poles of the cell

– The process of cytokinesis divides the cell into two genetically identical cells


METAPHASE TELOPHASE AND CYTOKINESIS

Metaphaseplate

Spindle Daughterchromosomes

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

ANAPHASE

Figure 8.6 (continued)


• In animals, cytokinesis occurs by cleavage

– This process pinches the cell apart

8.7 Cytokinesis differs for plant and animal cells

Figure 8.7A

Cleavagefurrow

Cleavagefurrow

Contracting ring ofmicrofilaments

Daughter cells


• In plants, a membranous cell plate splits the cell in two

Vesicles containingcell wall material

Cell plateforming

Figure 8.7BCell plate Daughter

cells

Wall ofparent cell

Daughternucleus

Cell wall New cell wall


• Most animal cells divide only when stimulated, and others not at all

• In laboratory cultures, most normal cells divide only when attached to a surface

– They are anchorage dependent

8.8 Anchorage, cell density, and chemical growth factors affect cell division


• Cells continue dividing until they touch one another

– This is called density-dependent inhibition

Cells anchor to dish surface and divide.

Figure 8.8A

When cells have formed a complete single layer, they stop dividing (density-dependent inhibition).

If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).


• Growth factors are proteins secreted by cells that stimulate other cells to divide

After forming a single layer, cells have stopped dividing.

Figure 8.8B

Providing an additional supply of growth factors stimulates further cell division.


• Proteins within the cell control the cell cycle

– Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide

8.9 Growth factors signal the cell cycle control system

G1 checkpoint

M checkpoint G2 checkpoint

Controlsystem

Figure 8.9A


• The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division

Growth factor

Figure 8.8B

Cell cyclecontrolsystem

Plasma membrane

Receptorprotein

Signal transduction pathway

G1 checkpointRelayproteins


• Cancer cells have abnormal cell cycles

– They divide excessively and can form abnormal masses called tumors

• Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

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


• Malignant tumors can invade other tissues and may kill the organism

Tumor

Figure 8.10

Glandulartissue

1 2 3A tumor grows from a single cancer cell.

Cancer cells invade neighboring tissue.

Lymphvessels

Cancer cells spread through lymph and blood vessels to other parts of the body.

Metastasis


• When the cell cycle operates normally, mitotic cell division functions in:

– Growth (seen here in an onion root)

8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction

Figure 8.11A


• Cell replacement (seen here in skin)

Deadcells

Figure 8.11B

Dividingcells

Epidermis, the outer layer of the skin

Dermis


• Asexual reproduction (seen here in a hydra)

Figure 8.11C


Fourth Edition






Modules 8.12 – 8.18


• Somatic cells of each species contain a specific number of chromosomes

– Human cells have 46, making up 23 pairs of homologous chromosomes

MEIOSIS AND CROSSING OVER

8.12 Chromosomes are matched in homologous pairs

Chromosomes

Centromere

Sister chromatids Figure 8.12


• Cells with two sets of chromosomes are said to be diploid

• Gametes are haploid, with only one set of chromosomes

8.13 Gametes have a single set of chromosomes


• At fertilization, a sperm fuses with an egg, forming a diploid zygote

– Repeated mitotic divisions lead to the development of a mature adult

– The adult makes haploid gametes by meiosis

– All of these processes make up the sexual life cycle of organisms


• The human life cycle

Figure 8.13

MEIOSIS FERTILIZATION

Haploid gametes (n = 23)

Egg cell

Sperm cell

Diploidzygote

(2n = 46)Multicellular

diploid adults (2n = 46)

Mitosis anddevelopment


• Meiosis, like mitosis, is preceded by chromosome duplication

– However, in meiosis the cell divides twice to form four daughter cells

8.14 Meiosis reduces the chromosome number from diploid to haploid


• In the first division, meiosis I, homologous chromosomes are paired

– While they are paired, they cross over and exchange genetic information

– The homologous pairs are then separated, and two daughter cells are produced


Figure 8.14, part 1

MEIOSIS I: Homologous chromosomes separate

INTERPHASE PROPHASE I METAPHASE I ANAPHASE I

Centrosomes(withcentriolepairs)

Nuclearenvelope

Chromatin

Sites of crossing over

Spindle

Sisterchromatids

Tetrad

Microtubules attached tokinetochore

Metaphaseplate

Centromere(with kinetochore)

Sister chromatidsremain attached

Homologouschromosomes separate


• Meiosis II is essentially the same as mitosis– The sister chromatids of each

chromosome separate

– The result is four haploid daughter cells


Figure 8.14, part 2

MEIOSIS II: Sister chromatids separate

TELOPHASE IAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II

Cleavagefurrow

Sister chromatidsseparate

TELOPHASE IIAND CYTOKINESIS

Haploiddaughter cellsforming


• For both processes, chromosomes replicate only once, during interphase

8.15 Review: A comparison of mitosis and meiosis


Figure 8.15

MITOSIS MEIOSIS

PARENT CELL(before chromosome replication)

Site ofcrossing over

MEIOSIS I

PROPHASE ITetrad formedby synapsis of homologous chromosomes

PROPHASE

Duplicatedchromosome(two sister chromatids)

METAPHASE

Chromosomereplication

Chromosomereplication

2n = 4

ANAPHASETELOPHASE

Chromosomes align at the metaphase plate

Tetradsalign at themetaphase plate

METAPHASE I

ANAPHASE ITELOPHASE I

Sister chromatidsseparate duringanaphase

Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together

No further chromosomal replication; sister chromatids separate during anaphase II

2n 2n

Daughter cellsof mitosis

Daughter cells of meiosis II

MEIOSIS II

Daughtercells of

meiosis I

Haploidn = 2

n n n n


• Each chromosome of a homologous pair comes from a different parent

– Each chromosome thus differs at many points from the other member of the pair

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


• The large number of possible arrangements of chromosome pairs at metaphase I of meiosis leads to many different combinations of chromosomes in gametes• Random fertilization also increases variation in offspring


Figure 8.16

POSSIBILITY 1 POSSIBILITY 2

Two equally probable

arrangements of chromosomes at

metaphase I

Metaphase II

Gametes

Combination 1 Combination 2 Combination 3 Combination 4


• The differences between homologous chromosomes are based on the fact that they can carry different versions of a gene at corresponding loci

8.17 Homologous chromosomes carry different versions of genes


Figure 8.17A, B

Coat-color genes Eye-color genes

Brown Black

C E

c e

White Pink

C E

c e

C E

c e

Tetrad in parent cell(homologous pair of

duplicated chromosomes)

Chromosomes ofthe four gametes


• Crossing over is the exchange of corresponding segments between two homologous chromosomes

• Genetic recombination results from crossing over during prophase I of meiosis

– This increases variation further

8.18 Crossing over further increases genetic variability


Figure 8.18A

TetradChaisma

Centromere


• How crossing over leads to genetic recombination

Figure 8.18B

Tetrad(homologous pair ofchromosomes in synapsis)

Breakage of homologous chromatids

Joining of homologous chromatids

Chiasma

Separation of homologouschromosomes at anaphase I

Separation of chromatids atanaphase II and completion of meiosis

Parental type of chromosome

Recombinant chromosome

Recombinant chromosome

Parental type of chromosome

Gametes of four genetic types

1

2

3

4

Coat-colorgenes

Eye-colorgenes


Fourth Edition






Modules 8.19 – 8.23


• To study human chromosomes microscopically, researchers stain and display them as a karyotype

– A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes

ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE

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


• Preparation of a karyotype

Figure 8.19

Blood culture

1

Centrifuge

Packed redAnd white blood cells

Fluid

2

Hypotonic solution

3

Fixative

WhiteBloodcells

Stain

4 5

Centromere

Sisterchromatids

Pair of homologouschromosomes


• This karyotype shows three number 21 chromosomes

• An extra copy of chromosome 21 causes Down syndrome

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

Figure 8.20A, B


• The chance of having a Down syndrome child goes up with maternal age

Figure 8.20C


• Abnormal chromosome count is a result of nondisjunction

– Either homologous pairs fail to separate during meiosis I

8.21 Accidents during meiosis can alter chromosome number

Figure 8.21A

Nondisjunctionin meiosis I

Normalmeiosis II

Gametes

n + 1 n + 1 n – 1 n – 1

Number of chromosomes


– Or sister chromatids fail to separate during meiosis II

Figure 8.21B

Normalmeiosis I

Nondisjunctionin meiosis II

Gametes

n + 1 n – 1 n n

Number of chromosomes


• Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome

Figure 8.21C

Eggcell

Spermcell

n + 1

n (normal)

Zygote2n + 1


• Nondisjunction can also produce gametes with extra or missing sex chromosomes

– Unusual numbers of sex chromosomes upset the genetic balance less than an unusual number of autosomes

8.22 Connection: Abnormal numbers of sex chromosomes do not usually affect survival


Table 8.22


• A man with Klinefelter syndrome has an extra X chromosome

Figure 8.22A

Poor beardgrowth

Under-developedtestes

Breastdevelopment


• A woman with Turner syndrome lacks an X chromosome

Figure 8.22B

Characteristicfacialfeatures

Web ofskin

Constrictionof aorta

Poorbreastdevelopment

Under-developedovaries


• Chromosome breakage can lead to rearrangements that can produce genetic disorders or cancer

– Four types of rearrangement are deletion, duplication, inversion, and translocation

8.23 Connection: Alterations of chromosome structure can cause birth defects and cancer


Figure 8.23A, B

Deletion

Duplication

Inversion

Homologouschromosomes

Reciprocaltranslocatio

n

Nonhomologouschromosomes


• Chromosomal changes in a somatic cell can cause cancer

Figure 8.23C

Chromosome 9

– A chromosomal translocation in the bone marrow is associated with chronic myelogenous leukemia

Chromosome 22Reciprocaltranslocation

“Philadelphia chromosome”

Activated cancer-causing gene


Fourth Edition




CHAPTER 8Extra Photographs


• Sea urchin development

Figure 8.0x


• E. coli dividing

Figure 8.3x


• Cell cycle collage

Figure 8.5x


• Mitosis collage, light micrographs

Figure 8.6x1


• Mitotic spindle

Figure 8.6x2


• Fibroblast growth

Figure 8.8x


• Breast cancer cell

Figure 8.10x1


• Mammograms

Figure 8.10x2


• Human female bands

Figure 8.19x1


• Human female karyotype

Figure 8.19x2


• Human male bands

Figure 8.19x3


• Human male karyotype

Figure 8.19x4


• Down syndrome karyotype

Figure 8.20Ax


• Klinefelter’s karyotype

Figure 8.22Ax


• XYY karyotype

Figure 8.22x


• Translocation

Figure 8.23Bx

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CHAPTER 8 The Cellular Basis of Reproduction and Inheritance