_08_Lecture_Presentation_PC.ppt

(1)

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey

Chapter 8

(2)



Cancer cells

– start out as normal body cells,

– undergo genetic mutations,

– lose the ability to control the tempo of their own division, and

– run amok, causing disease.

Introduction

(3)



In a healthy body, cell division allows for

– growth,

– the replacement of damaged cells, and

– development from an embryo into an adult.



In sexually reproducing organisms, eggs and sperm

result from

– mitosis and

– meiosis.

Introduction

(4)

(5)

Figure 8.0_2

Chapter 8: Big Ideas

Cell Division and

Reproduction The Eukaryotic CellCycle and Mitosis

Meiosis and Crossing Over

(6)

(7)

CELL DIVISION AND

REPRODUCTION

(8)

8.1 Cell division plays many important roles in

the lives of organisms



Organisms reproduce their own kind, a key

characteristic of life.



Cell division

– is reproduction at the cellular level,

– requires the duplication of chromosomes, and

– sorts new sets of chromosomes into the resulting pair of daughter cells.

(9)



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, and

– sperm and egg production.

the lives of organisms

(10)

the lives of organisms



Living organisms reproduce by two methods.

– Asexual reproduction

– produces offspring that are identical to the original cell or organism and

– involves inheritance of all genes from one parent.

– Sexual reproduction

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

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

(11)

(12)

(13)

(14)

(15)

(16)

(17)



Prokaryotes

(bacteria and archaea) reproduce by

binary fission

(“dividing in half”).



The chromosome of a prokaryote is

– a singular circular DNA molecule associated with proteins and

– much smaller than those of eukaryotes.

8.2 Prokaryotes reproduce by binary fission

(18)



Binary fission of a prokaryote occurs in three stages:

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

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

3. division into two daughter cells.

8.2 Prokaryotes reproduce by binary fission

(19)

Figure 8.2A_s1

Plasma membrane

Cell wall

Duplication of the chromosome and separation of the copies

Prokaryotic chromosome

(20)

Figure 8.2A_s2

Plasma membrane

Cell wall

Continued elongation of the cell and movement of the copies

1

(21)

Figure 8.2A_s3

Plasma membrane

Cell wall

Continued elongation of the cell and movement of the copies

1

2

3 Division into

(22)

Figure 8.2B

(23)

THE EUKARYOTIC CELL

CYCLE AND MITOSIS

(24)



Eukaryotic cells

– are more complex and larger than prokaryotic cells,

– have more genes, and

– store most of their genes on multiple chromosomes within the nucleus.

8.3 The large, complex chromosomes of

eukaryotes duplicate with each cell division

(25)



Eukaryotic chromosomes are composed of

chromatin

consisting of

– one long DNA molecule and

– proteins that help maintain the chromosome structure and control the activity of its genes.



To prepare for division, the chromatin becomes

– highly compact and

– visible with a microscope.

8.3 The large, complex chromosomes of

(26)

(27)

(28)

Figure 8.3B_2

Sister chromatids

(29)



Before a eukaryotic cell begins to divide, 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.

8.3 The large, complex chromosomes of

(30)

Figure 8.3B_1

Chromosomes

Centromere

Chromosome duplication

Sister

chromatids

Chromosome distribution

to the daughter

cells

(31)



The

cell cycle

is an ordered sequence of events

that extends

– from the time a cell is first formed from a dividing parent cell

– until its own division.

8.4 The cell cycle multiplies cells

(32)



The cell cycle consists of two stages,

characterized as follows:

1. Interphase: duplication of cell contents – _G₁_{—growth, increase in cytoplasm}

– S—duplication of chromosomes

– _G₂_{—growth, preparation for division}

2. Mitotic phase: division

– Mitosis—division of the nucleus

– Cytokinesis—division of cytoplasm

8.4 The cell cycle multiplies cells

(33)

Figure 8.4

G₁

(first gap) _{(DNA synthesis)}S

G2 (second gap) M Cytokine sis Mito sis

I N T E R P H A S E

(34)



Mitosis progresses through a series of stages:

– prophase,

– prometaphase,

– metaphase,

– anaphase, and

– telophase.



Cytokinesis often overlaps telophase.

8.5 Cell division is a continuum of dynamic

changes

(35)



A

mitotic spindle

is

– required to divide the chromosomes,

– _{composed of microtubules, and}

– produced by centrosomes, structures in the cytoplasm that

– organize microtubule arrangement and

– contain a pair of centrioles in animal cells.

8.5 Cell division is a continuum of dynamic

changes

(36)

Video: Animal Mitosis

(37)



A

mitotic spindle

is

– required to divide the chromosomes,

– _{composed of microtubules, and}

– produced by centrosomes, structures in the cytoplasm that

– organize microtubule arrangement and

– contain a pair of centrioles in animal cells.

8.5 Cell division is a continuum of dynamic

changes

(38)

Figure 8.5_1 INTERPHASE MITOSIS Prophase Prometaphase Centrosome Early mitotic spindle Chromatin Fragments of the nuclear envelope Kinetochore Centrosomes

(with centriole pairs)

Centrioles

Nuclear

envelope Plasma_membrane Chromosome,consisting of two sister chromatids

Centromere

Spindle

(39)



Interphase

– The cytoplasmic contents double,

– two centrosomes form,

– chromosomes duplicate in the nucleus during the S phase, and

– nucleoli, sites of ribosome assembly, are visible.

changes

(40)

Figure 8.5_2

(41)

Figure 8.5_left INTERPHASE MITOSIS Prophase Prometaphase Centrosome Early mitotic spindle Chromatin Fragments of

the nuclear envelope Kinetochore Centrosomes

(with centriole pairs) Centrioles

Nuclear

envelope Plasma_membrane Chromosome, consisting of two sister chromatids

Centromere Spindle

(42)



Prophase

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

– In the nucleus

– chromosomes coil and become compact and

– nucleoli disappear.

changes

(43)

Figure 8.5_3

(44)



Prometaphase

– Spindle microtubules reach chromosomes, where they – attach at kinetochores on the centromeres of sister

chromatids and

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

– Other microtubules meet those from the opposite poles.

– The nuclear envelope disappears.

8.5 Cell division is a continuum of dynamic

changes

(45)

Figure 8.5_4

(46)

Figure 8.5_5

MITOSIS Anaphase

Metaphase Telophase and Cytokinesis

Metaphase

plate Cleavage

furrow

Nuclear envelope forming Daughter

chromosomes Mitotic

(47)

Figure 8.5_right

MITOSIS Anaphase

Metaphase Telophase and Cytokinesis

(48)



Metaphase

– The mitotic spindle is fully formed.

– Chromosomes align at the cell equator.

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

changes

(49)

Figure 8.5_6

(50)



Anaphase

– Sister chromatids separate at the centromeres.

– Daughter chromosomes are moved to opposite poles of the cell as

– motor proteins move the chromosomes along the spindle microtubules and

– kinetochore microtubules shorten.

– The cell elongates due to lengthening of nonkinetochore microtubules.

8.5 Cell division is a continuum of dynamic

changes

(51)

Figure 8.5_7

(52)



Telophase

– The cell continues to elongate.

– The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei.

– _{Chromatin uncoils and nucleoli reappear.} – The spindle disappears.

changes

(53)

Figure 8.5_8

(54)



During

cytokinesis

, the cytoplasm is divided into

separate cells.



The process of cytokinesis differs in animal and

plant cells.

changes

(55)



In animal cells, cytokinesis occurs as

1. a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, and

2. the cleavage furrow deepens to separate the contents into two cells.

8.6 Cytokinesis differs for plant and animal cells

(56)

Figure 8.6A

Cytokinesis

Cleavage

furrow Contracting ring of

microfilaments

Daughter cells

(57)

Figure 8.6A_1

(58)

Figure 8.6A_2

Cleavage

furrow Contracting ring of microfilaments

(59)



In plant cells, cytokinesis occurs as

1. a cell plate forms in the middle, from vesicles containing cell wall material,

2. the cell plate grows outward to reach the edges, dividing the contents into two cells,

3. each cell now possesses a plasma membrane and cell wall.

8.6 Cytokinesis differs for plant and animal cells

(60)

Animation: Cytokinesis

(61)

Figure 8.6B Cytokinesis Cell wall of the parent cell Daughter nucleus Cell wall Plasma membrane Vesicles containing cell wall material Cell plate forming New cell wall

Cell plate Daughter

(62)

Figure 8.6B_1

Cell wall of the

parent cell

Daughter nucleus

(63)

Figure 8.6B_2

Cell wall Plasma

membrane

Vesicles containing cell wall material

New

cell wall

(64)



The cells within an organism’s body divide and

develop at different rates.



Cell division is controlled by

– the presence of essential nutrients,

– growth factors, proteins that stimulate division,

– density-dependent inhibition, in which crowded cells stop dividing, and

– anchorage dependence, the need for cells to be in contact with a solid surface to divide.

8.7 Anchorage, cell density, and chemical growth

factors affect cell division

(65)

Figure 8.7A

Cultured cells

suspended in liquid

The addition of growth

(66)

Figure 8.7B

Anchorage

Single layer of cells

Removal of cells

(67)



The

cell cycle control system

is a cycling set of

molecules in the cell that

– triggers and

– coordinates key events in the cell cycle.



Checkpoints in the cell cycle can

– stop an event or

– signal an event to proceed.

8.8 Growth factors signal the cell cycle control

system

(68)



There are three major checkpoints in the cell cycle.

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, and

3. M checkpoint.



Research on the control of the cell cycle is one of

the hottest areas in biology today.

8.8 Growth factors signal the cell cycle control

system

(69)

Figure 8.8A

G₀

G1 checkpoint

G₁

S

M

G₂ Control

system

M checkpoint

(70)

Figure 8.8B Receptor protein Signal transduction pathway Growth factor Relay proteins

Plasma membrane EXTRACELLULAR FLUID

CYTOPLASM

G₁

checkpoint

G₁ S

M

G₂ Control

(71)



Cancer currently claims the lives of 20% of the

people in the United States and other

industrialized nations.



Cancer cells escape controls on the cell cycle.



Cancer cells

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

– spread to other tissues through the circulatory system, and

– grow without being inhibited by other cells.

8.9 CONNECTION: Growing out of control,

cancer cells produce malignant tumors

(72)



A

tumor

is an abnormally growing mass of body

cells.

– Benign tumors remain at the original site.

– Malignant tumors spread to other locations, called

metastasis.

8.9 CONNECTION: Growing out of control,

(73)

Figure 8.9

Tumor

Glandular tissue

Growth Invasion Metastasis

Lymph vessels Blood vessel

(74)



Cancers are named according to the organ or

tissue in which they originate.

– Carcinomas arise in external or internal body coverings.

– Sarcomas arise in supportive and connective tissue.

– Leukemias and lymphomas arise from blood-forming tissues.

(75)



Cancer treatments

– Localized tumors can be – removed surgically and/or

– treated with concentrated beams of high-energy radiation.

– Chemotherapy is used for metastatic tumors.

(76)



When the cell cycle operates normally, mitosis

produces genetically identical cells for

– growth,

– replacement of damaged and lost cells, and

– asexual reproduction.

8.10 Review: Mitosis provides for growth, cell

replacement, and asexual reproduction

(77)

Video: Hydra Budding

(78)

(79)

(80)

(81)

(82)

MEIOSIS AND

CROSSING OVER

(83)



In humans,

somatic cells

have

– 23 pairs of homologous chromosomes and

– one member of each pair from each parent.



The human

sex chromosomes

X and Y differ in

size and genetic composition.



The other 22 pairs of chromosomes are

autosomes

with the same size and genetic

composition.

8.11 Chromosomes are matched in homologous

pairs

(84)



Homologous chromosomes

are matched in

– length,

– centromere position, and

– gene locations.



A

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.

8.11 Chromosomes are matched in homologous

pairs

(85)

Figure 8.11

Pair of homologous chromosomes

Locus

Centromere

Sister

chromatids

(86)



An organism’s

life cycle

is the sequence of

stages leading

– from the adults of one generation

– to the adults of the next.



Humans and many animals and plants are diploid,

with body cells that have

– two sets of chromosomes,

– one from each parent.

8.12 Gametes have a single set of chromosomes

(87)



Meiosis is a process that converts diploid nuclei to

haploid nuclei.

– Diploid cells have two homologous sets of chromosomes.

– Haploid cells have one set of chromosomes.

– 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.

8.12 Gametes have a single set of chromosomes

(88)

Figure 8.12A

Haploid gametes (n  23)

Egg cell Sperm cell Fertilization n n Meiosis Ovary Testis Diploid zygote (2n  46)

2n

Mitosis

Key

Haploid stage (n) Diploid stage (2n) Multicellular diploid

(89)



All sexual life cycles include an alternation

between

– a diploid stage and

– a haploid stage.



Producing haploid gametes prevents the

chromosome number from doubling in every

generation.

8.12 Gametes have a single set of chromosomes

(90)

Figure 8.12B

A pair of

homologous chromosomes in a diploid parent cell

A pair of duplicated homologous chromosomes Sister

chromatids

1 2 3

(91)



Meiosis

is a type of cell division that produces

haploid gametes in diploid organisms.



Two haploid gametes combine in fertilization to

restore the diploid state in the zygote.

8.13 Meiosis reduces the chromosome number

from diploid to haploid

(92)



Meiosis and mitosis are preceded by the duplication

of chromosomes. However,

– meiosis is followed by two consecutive cell divisions and

– mitosis is followed by only one cell division.



Because in meiosis, one duplication of

chromosomes is followed by two divisions, each of

the four daughter cells produced has a haploid set of

chromosomes.

8.13 Meiosis reduces the chromosome number

(93)



Meiosis I

–

Prophase I

– events occurring in the

nucleus.

– 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.

8.13 Meiosis reduces the chromosome number

(94)

Figure 8.13_left

Centrosomes (with centriole

pairs) _Centrioles

Sites of crossing over Spindle Tetrad Nuclear envelope Chromatin Sister chromatids Fragments of the nuclear envelope Centromere (with a kinetochore) Spindle microtubules attached to a kinetochore

Metaphase plate _Homologous chromosomes separate Sister chromatids remain attached

Chromosomes duplicateINTERPHASE: _Prophase_I _Metaphase_I _Anaphase_I

(95)

Figure 8.13_1

Centrosomes (with centriole

pairs) _Centrioles

Sites of crossing over

Spindle Tetrad Nuclear envelope Chromatin Sister chromatids Fragments of the nuclear envelope Chromosomes duplicateINTERPHASE: _{Prophase I}

(96)

Figure 8.13_2

Centromere (with a

kinetochore)

Spindle microtubules

attached to a kinetochore

Metaphase

plate _Homologous chromosomes separate

Sister chromatids remain attached Metaphase I Anaphase I

(97)



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.

(98)



Meiosis I

–

Telophase I

– Duplicated chromosomes have reached the poles.

– A nuclear envelope re-forms around chromosomes in some species.

– Each nucleus has the haploid number of chromosomes.

8.13 Meiosis reduces the chromosome number

(99)



Meiosis

II

follows meiosis

I

without chromosome

duplication.



Each of the two haploid products enters meiosis

II

.



Meiosis II

–

Prophase II

– Chromosomes coil and become compact (if uncoiled after telophase I).

– Nuclear envelope, if re-formed, breaks up again.

8.13 Meiosis reduces the chromosome number

(100)

Figure 8.13_right

Cleavage furrow

Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II

MEIOSISII: Sister chromatids separate

Sister chromatids

separate Haploid daughter_{cells forming} Telophase II

(101)

Figure 8.13_3

Cleavage furrow

(102)

Figure 8.13_4

Prophase II Metaphase II Anaphase II

MEIOSIS II: Sister chromatids separate

Sister chromatids

(103)

Figure 8.13_5

Two lily cells

(104)



Meiosis II

–

Metaphase II

– Duplicated

chromosomes align at the cell equator.



Meiosis II

–

Anaphase II

– Sister chromatids separate and

– chromosomes move toward opposite poles.

(105)



Meiosis II

–

Telophase II

– Chromosomes have reached the poles of the cell.

– _{A nuclear envelope forms around each set of}

chromosomes.

– With cytokinesis, four haploid cells are produced.

8.13 Meiosis reduces the chromosome number

(106)



Mitosis and meiosis both

– begin with diploid parent cells that

– have chromosomes duplicated during the previous interphase.



However the end products differ.

– Mitosis produces two genetically identical diploid somatic daughter cells.

– Meiosis produces four genetically unique haploid gametes.

8.14 Mitosis and meiosis have important

similarities and differences

(107)

Figure 8.14 Prophase Metaphase Duplicated chromosome (two sister chromatids) MITOSIS Parent cell

(before chromosome duplication)

Chromosome

duplication Chromosomeduplication Site of crossing over

2n 4

Chromosomes align at the metaphase plate

Tetrads (homologous pairs) align at the metaphase plate

Tetrad formed by synapsis of homologous chromosomes

Metaphase I Prophase I MEIOSISI

Anaphase Telophase

Sister chromatids separate during

anaphase

2n 2n

Daughter cells of mitosis

No further chromosomal duplication; sister chromatids separate during anaphase II

n n n n

Daughter cells of meiosis II Daughter

cells of meiosis I

Haploid

n 2 Anaphase I Telophase I Homologous

chromosomes separate during anaphase I; sister chromatids remain together

(108)

Figure 8.14_1

Prophase

Metaphase MITOSIS

Parent cell

(before chromosome duplication)

Chromosome

duplication Chromosomeduplication

Site of crossing over

2n  4

Chromosomes align at the

metaphase plate

Tetrad

Metaphase I

Prophase I

(109)

Figure 8.14_2

Metaphase

MITOSIS

Chromosomes align at the

metaphase plate

Anaphase Telophase

Sister chromatids separate during

anaphase

2n 2n

(110)

Figure 8.14_3

Metaphase I

No further chromosomal duplication; sister chromatids separate during anaphase II

n

Daughter cells of meiosis II

Daughter cells of meiosis I

Haploid

n  2 Anaphase I

Telophase I

Homologous chromosomes separate during anaphase I; sister

chromatids remain together

MEIOSIS II

MEIOSIS I

(111)



Genetic variation in gametes results from

– independent orientation at metaphase I and

– random fertilization.

8.15 Independent orientation of chromosomes in

meiosis and random fertilization lead to

varied offspring

(112)



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.

8.15 Independent orientation of chromosomes in

varied offspring

(113)



Random fertilization – The combination of each

unique sperm with each unique egg increases

genetic variability.

8.15 Independent orientation of chromosomes in

varied offspring

(114)

Animation: Genetic Variation

(115)

Figure 8.15_s1

Possibility A

Two equally probable arrangements of chromosomes at

metaphase I

(116)

Figure 8.15_s2

Possibility A

metaphase I

Possibility B

(117)

Figure 8.15_s3

Possibility A

metaphase I

Possibility B

Metaphase II

Gametes

Combination 3 Combination 4 Combination 2

(118)

8.16 Homologous chromosomes may carry

different versions of genes



Separation of homologous chromosomes during

meiosis can lead to genetic differences between

gametes.

– Homologous chromosomes may have different versions of a gene at the same locus.

– One version was inherited from the maternal parent and the other came from the paternal parent.

– Since homologues move to opposite poles during

anaphase I, gametes will receive either the maternal or paternal version of the gene.

(119)

Figure 8.16

Coat-color

genes Eye-colorgenes

Brown Black

Meiosis

White Pink

Tetrad in parent cell (homologous pair of duplicated chromosomes)

Chromosomes of

the four gametes _{White coat (}_c_); pink eyes (e) Brown coat (C);

black eyes (E)

(120)

Figure 8.16_2

(121)

Figure 8.16_3

(122)

Figure 8.16_1

Coat-color

genes Eye-colorgenes

Brown Black

Meiosis

White Pink

Tetrad in parent cell (homologous pair of duplicated chromosomes) E C e c Chromosomes of the four gametes

(123)

Figure 8.16Q

Sister chromatids Sister chromatids

(124)



Genetic recombination

is the production of new

combinations of genes due to crossing over.



Crossing over

is an exchange of corresponding

segments between separate (nonsister)

chromatids on homologous chromosomes.

– 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.

8.17 Crossing over further increases genetic

variability

(125)

Animation: Crossing Over

(126)

Figure 8.17A

Chiasma

(127)

Figure 8.17A_1

(128)

Figure 8.17B

Tetrad

(pair of homologous chromosomes in synapsis)

Breakage of homologous chromatids

Joining of homologous chromatids

Chiasma

Separation of homologous chromosomes at anaphase I

Separation of chromatids at anaphase II and

completion of meiosis

Parental type of chromosome

Recombinant chromosome

Parental type of chromosome Gametes of four genetic types

(129)

Figure 8.17B_1

Tetrad

(pair of homologous

chromosomes in synapsis)

Breakage of homologous chromatids

Joining of homologous chromatids

(130)

Figure 8.17B_2

Separation of homologous chromosomes at anaphase I

3

C E

C e

Chiasma

c

E

e

C E

(131)

Figure 8.17B_3

Separation of chromatids at anaphase II and

completion of meiosis

Parental type of chromosome

Recombinant chromosome

Parental type of chromosome Gametes of four genetic types

(132)

ALTERATIONS OF

CHROMOSOME NUMBER

AND STRUCTURE

(133)



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.

8.18 A karyotype is a photographic inventory of

an individual’s chromosomes

(134)

Figure 8.18_s1

Blood culture

Packed red and white blood cells

Centrifuge

(135)

Figure 8.18_s2

Blood culture

Packed red and white blood cells

Centrifuge

Fluid

Hypotonic solution

2

(136)

(137)

Figure 8.18_s4

(138)

Figure 8.18_s5

Centromere

Sister

chromatids

Pair of

homologous chromosomes

5

(139)



Trisomy 21

– involves the inheritance of three copies of chromosome 21 and

– is the most common human chromosome abnormality.

8.19 CONNECTION: An extra copy of

chromosome 21 causes Down syndrome

(140)



Trisomy 21,

called

Down syndrome,

produces a

characteristic set of symptoms, which include:

– mental retardation,

– characteristic facial features,

– short stature,

– heart defects,

– susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, and

– shortened life span.



The incidence increases with the age of the mother.

8.19 CONNECTION: An extra copy of

chromosome 21 causes Down syndrome

(141)

Figure 8.19A

(142)

Figure 8.19A_1

(143)

(144)

Figure 8.19B

Age of mother

(145)



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.

8.20 Accidents during meiosis can alter

chromosome number

(146)

Figure 8.20A_s1

Nondisjunction

(147)

Figure 8.20A_s2

Nondisjunction

MEIOSIS I

MEIOSIS II

(148)

Figure 8.20A_s3

Nondisjunction

MEIOSIS I

MEIOSIS II

Normal meiosis II

Gametes

Number of chromosomes

Abnormal gametes

(149)

Figure 8.20B_s1

Normal meiosis I

(150)

Figure 8.20B_s2

Normal meiosis I

MEIOSIS I

MEIOSIS II

(151)

Figure 8.20B_s3

Normal meiosis I

MEIOSIS I

MEIOSIS II

Nondisjunction

Abnormal gametes Normal gametes

(152)



Sex chromosome abnormalities tend to be less

severe, perhaps because of

– the small size of the Y chromosome or

– X-chromosome inactivation.

8.21 CONNECTION: Abnormal numbers of sex

chromosomes do not usually affect survival

(153)



The following table lists the most common human

sex chromosome abnormalities. In general,

– a single Y chromosome is enough to produce “maleness,” even in combination with several X chromosomes, and

– the absence of a Y chromosome yields “femaleness.”

8.21 CONNECTION: Abnormal numbers of sex

chromosomes do not usually affect survival

(154)

(155)



Errors in mitosis or meiosis may produce polyploid

species, with more than two chromosome sets

.



The formation of polyploid species is

– widely observed in many plant species but

– less frequently found in animals.

8.22 EVOLUTION CONNECTION: New species

can arise from errors in cell division

(156)

(157)



Chromosome breakage can lead to

rearrangements that can produce

– genetic disorders or,

– if changes occur in somatic cells, cancer.

8.23 CONNECTION: Alterations of chromosome

structure can cause birth defects and cancer

(158)



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.

(159)



Chronic myelogenous leukemia (CML)

– is one of the most common leukemias,

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

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

(160)

Figure 8.23A

Deletion

Duplication

Inversion

Reciprocal translocation

Homologous

(161)

Figure 8.23A_1

Deletion

Duplication

(162)

Figure 8.23A_2

Inversion

Reciprocal translocation

(163)

Figure 8.23B

Chromosome 9

Chromosome 22 Reciprocal

translocation

“Philadelphia chromosome”

(164)

1. Compare the parent-offspring relationship in asexual and sexual reproduction.

2. Explain why cell division is essential for prokaryotic and eukaryotic life.

3. Explain how daughter prokaryotic chromosomes are separated from each other during binary fission.

4. Compare the structure of prokaryotic and eukaryotic chromosomes.

5. Describe the stages of the cell cycle.

You should now be able to

(165)

6. List the phases of mitosis and describe the events characteristic of each phase.

7. Compare cytokinesis in animal and plant cells.

8. Explain how anchorage, cell density, and chemical growth factors control cell division.

9. Explain how cancerous cells are different from healthy cells.

10. Describe the functions of mitosis.

11. Explain how chromosomes are paired.

12. Distinguish between somatic cells and gametes and between diploid cells and haploid cells.

You should now be able to

(166)

13. Explain why sexual reproduction requires meiosis.

14. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase.

15. Compare mitosis and meiosis noting similarities and differences.

16. Explain how genetic variation is produced in sexually reproducing organisms.

17. Explain how and why karyotyping is performed.

18. Describe the causes and symptoms of Down syndrome.

You should now be able to

(167)

19. Describe the consequences of abnormal numbers of sex chromosomes.

20. Define nondisjunction, explain how it can occur, and describe what can result.

21. Explain how new species form from errors in cell division.

22. Describe the main types of chromosomal changes. Explain why cancer is not usually inherited.

You should now be able to

(168)

PH A SE T T M I O IC Figure 8.UN01 Genetically identical daughter cells S G₁ G₂ M Mitosis (division of the nucleus) Cytokinesis

(division of the cytoplasm)

Cytokine

sis

Mito sis

I N T E R P H A S E

(169)

Figure 8.UN02

Haploid gametes (n  23) Egg cell Sperm cell Fertilization n n Meiosis

Human life cycle

2n Multicellular

diploid adults (2n  46)

Mitosis

(170)

Figure 8.UN03

Number of chromosomal duplications

Number of cell divisions

Number of daughter cells produced

Number of chromosomes in the daughter cells

How the chromosomes line up during metaphase

Genetic relationship of the

daughter cells to the parent cell

Functions performed in the human body

(171)