The Cellular Basis of Reproduction and Inheritance

The Cellular Basis of Reproduction and Inheritance
Chapter 8 The Cellular Basis of Reproduction and Inheritance

Introduction Cancer cells start out as normal body cells,
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. © 2012 Pearson Education, Inc. 2

Introduction In a healthy body, cell division allows for
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. © 2012 Pearson Education, Inc. 3

Alterations of Chromosome
Figure 8.0_2 Chapter 8: Big Ideas Cell Division and Reproduction The Eukaryotic Cell Cycle and Mitosis Figure 8.0_2 Chapter 8: Big Ideas Meiosis and Crossing Over Alterations of Chromosome Number and Structure 4

Figure 8.0_3 Figure 8.0_3 Dividing cancer cells 5

CELL DIVISION AND REPRODUCTION
© 2012 Pearson Education, Inc. 6

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. © 2012 Pearson Education, Inc. 7

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. © 2012 Pearson Education, Inc. 8

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. © 2012 Pearson Education, Inc. 9

Figure 8.1A A yeast cell producing a genetically identical daughter cell by asexual reproduction
10

THE EUKARYOTIC CELL CYCLE AND MITOSIS

8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
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. © 2012 Pearson Education, Inc. 12

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. © 2012 Pearson Education, Inc. 13

Figure 8.3A Figure 8.3A A plant cell (from an African blood lily) just before cell division 14

Chromosomes DNA molecules Sister chromatids Chromosome duplication
Figure 8.3B Chromosomes DNA molecules Sister chromatids Chromosome duplication Sister chromatids Centromere Figure 8.3B Chromosome duplication and distribution Chromosome distribution to the daughter cells 15

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. © 2012 Pearson Education, Inc. 16

Chromosomes DNA molecules Chromosome duplication Sister chromatids
Figure 8.3B_1 Chromosomes DNA molecules Chromosome duplication Sister chromatids Centromere Figure 8.3B_1 Chromosome duplication and distribution (part 1) Chromosome distribution to the daughter cells 17

8.4 The cell cycle multiplies cells
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. © 2012 Pearson Education, Inc. 18

8.4 The cell cycle multiplies cells
The cell cycle consists of two stages, characterized as follows: Interphase: duplication of cell contents G1—growth, increase in cytoplasm S—duplication of chromosomes G2—growth, preparation for division Mitotic phase: division Mitosis—division of the nucleus Cytokinesis—division of cytoplasm © 2012 Pearson Education, Inc. 19

I N T E R P H A S G1 (first gap) S (DNA synthesis) M G2 (second gap)
Figure 8.4 I N T E R P H A S G1 (first gap) S (DNA synthesis) M Cytokinesis G2 (second gap) Mitosis Figure 8.4 The eukaryotic cell cycle T MI O IC PH A SE 20

8.5 Cell division is a continuum of dynamic changes
Mitosis progresses through a series of stages: prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis often overlaps telophase. © 2012 Pearson Education, Inc. 21

(with centriole pairs) Fragments of the nuclear envelope Early mitotic
Figure 8.5_1 MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Fragments of the nuclear envelope Early mitotic spindle Centrosome Kinetochore Centrioles Chromatin Figure 8.5_1 The stages of cell division by mitosis: Interphase through Prometaphase Centromere Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Spindle microtubules 22

(with centriole pairs) Early mitotic spindle Fragments of
Figure 8.5_left MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Early mitotic spindle Fragments of the nuclear envelope Centrosome Chromatin Centrioles Kinetochore Figure 8.5_left The stages of cell division by mitosis: Interphase through Prometaphase Nuclear envelope Plasma membrane Centromere Chromosome, consisting of two sister chromatids Spindle microtubules 23

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. © 2012 Pearson Education, Inc. 24

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. © 2012 Pearson Education, Inc. 25

Figure 8.5_2 Figure 8.5_2 The stages of cell division by mitosis: Interphase INTERPHASE 26

Prophase In the cytoplasm microtubules begin to emerge from centrosomes, forming the spindle. In the nucleus chromosomes coil and become compact and nucleoli disappear. © 2012 Pearson Education, Inc. 27

Figure 8.5_3 Figure 8.5_3 The stages of cell division by mitosis: Prophase Prophase 28

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. © 2012 Pearson Education, Inc. 29

Figure 8.5_4 Figure 8.5_4 The stages of cell division by mitosis: Prometaphase Prometaphase 30

(with centriole pairs) Early mitotic spindle Fragments of
Figure 8.5_left MITOSIS INTERPHASE Prophase Prometaphase Centrosomes (with centriole pairs) Early mitotic spindle Fragments of the nuclear envelope Centrosome Chromatin Centrioles Kinetochore Figure 8.5_left The stages of cell division by mitosis: Interphase through Prometaphase Nuclear envelope Plasma membrane Centromere Chromosome, consisting of two sister chromatids Spindle microtubules 31

Telophase and Cytokinesis
Figure 8.5_5 MITOSIS Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Figure 8.5_5 The stages of cell division by mitosis: Metaphase through Cytokenesis Nuclear envelope forming Mitotic spindle Daughter chromosomes 32

Figure 8.5_right MITOSIS Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Figure 8.5_right The stages of cell division by mitosis: Metaphase through Cytokenesis Mitotic spindle Nuclear envelope forming Daughter chromosomes 33

Figure 8.5_6 Figure 8.5_6 The stages of cell division by mitosis: Metaphase Metaphase 35

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. © 2012 Pearson Education, Inc. 36

Figure 8.5_7 Figure 8.5_7 The stages of cell division by mitosis: Anaphase Anaphase 37

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. © 2012 Pearson Education, Inc. 38

Figure 8.5_8 Figure 8.5_8 The stages of cell division by mitosis: Telophase and Cytokenesis Telophase and Cytokinesis 39

Figure 8.5_right MITOSIS Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Figure 8.5_right The stages of cell division by mitosis: Metaphase through Cytokenesis Mitotic spindle Nuclear envelope forming Daughter chromosomes 40

8.6 Cytokinesis differs for plant and animal cells
In animal cells, cytokinesis occurs as a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, and the cleavage furrow deepens to separate the contents into two cells. © 2012 Pearson Education, Inc. 42

Cleavage furrow Daughter cells
Figure 8.6A Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8.6A Cleavage of an animal cell Cleavage furrow 43

8.6 Cytokinesis differs for plant and animal cells
In plant cells, cytokinesis occurs as 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 now possesses a plasma membrane and cell wall. © 2012 Pearson Education, Inc. 44

Cytokinesis New cell wall Cell wall of the parent cell Cell wall
Figure 8.6B Cytokinesis New cell wall Cell wall of the parent cell Cell wall Plasma membrane Daughter nucleus Vesicles containing cell wall material Cell plate Daughter cells Figure 8.6B Cell plate formation in a plant cell Cell plate forming 45

8.7 Anchorage, cell density, and chemical growth factors affect cell division
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. © 2012 Pearson Education, Inc. 46

Cultured cells suspended in liquid The addition of growth factor
Figure 8.7A Cultured cells suspended in liquid The addition of growth factor Figure 8.7A An experiment demonstrating the effect of growth factors on the division of cultured animal cells 47

Anchorage Single layer of cells Removal of cells Restoration of single
Figure 8.7B Anchorage Single layer of cells Removal of cells Figure 8.7B An experiment demonstrating density-dependent inhibition, using animal cells grown in culture Restoration of single layer by cell division 48

8.8 Growth factors signal the cell cycle control system
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. © 2012 Pearson Education, Inc. 49

8.8 Growth factors signal the cell cycle control system
There are three major checkpoints in the cell cycle. G1 checkpoint allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G0 phase. G2 checkpoint, and M checkpoint. Research on the control of the cell cycle is one of the hottest areas in biology today. © 2012 Pearson Education, Inc. 50

G1 checkpoint G0 G1 S Control system M G2 M checkpoint G2 checkpoint
Figure 8.8A G1 checkpoint G0 G1 S Control system M Figure 8.8A A schematic model for the cell cycle control system G2 M checkpoint G2 checkpoint 51

G1 checkpoint Receptor protein S G1 Control system M G2
Figure 8.8B EXTRACELLULAR FLUID Plasma membrane Growth factor Relay proteins G1 checkpoint Receptor protein Signal transduction pathway S G1 Control system Figure 8.8B How a growth factor signals the cell cycle control system M G2 CYTOPLASM 52

8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
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. © 2012 Pearson Education, Inc. 53

Lymph vessels Blood vessel Tumor Tumor in another part of the body
Figure 8.9 Lymph vessels Blood vessel Tumor Tumor in another part of the body Glandular tissue Figure 8.9 Growth and metastasis of a malignant (cancerous) tumor of the breast Growth Invasion Metastasis 55

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. © 2012 Pearson Education, Inc. 56

Cancer treatments Localized tumors can be removed surgically and/or treated with concentrated beams of high-energy radiation. Chemotherapy is used for metastatic tumors. © 2012 Pearson Education, Inc. 57

8.10 Review: Mitosis provides for growth, cell replacement, and asexual reproduction
When the cell cycle operates normally, mitosis produces genetically identical cells for growth, replacement of damaged and lost cells, and asexual reproduction. © 2012 Pearson Education, Inc. 58

Figure 8.10A Figure 8.10A Growth (in an onion root) 59

MEIOSIS AND CROSSING OVER

8.11 Chromosomes are matched in homologous pairs
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. © 2012 Pearson Education, Inc. 61

8.11 Chromosomes are matched in homologous pairs
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. © 2012 Pearson Education, Inc. 62

Pair of homologous chromosomes One duplicated chromosome
Figure 8.11 Pair of homologous chromosomes Locus Centromere Sister chromatids Figure 8.11 A pair of homologous chromosomes One duplicated chromosome 63

8.12 Gametes have a single set of chromosomes
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. © 2012 Pearson Education, Inc. 64

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. © 2012 Pearson Education, Inc. 65

Multicellular diploid adults (2n  46) Diploid stage (2n)
Figure 8.12A Haploid gametes (n  23) n Egg cell n Sperm cell Meiosis Fertilization Ovary Testis Figure 8.12A The human life cycle Diploid zygote (2n  46) 2n Key Mitosis Haploid stage (n) Multicellular diploid adults (2n  46) Diploid stage (2n) 66

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. © 2012 Pearson Education, Inc. 67

Sister chromatids A pair of homologous chromosomes in a diploid
Figure 8.12B INTERPHASE MEIOSIS I MEIOSIS II Sister chromatids 1 2 3 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes Figure 8.12B How meiosis halves chromosome number 68

8.13 Meiosis reduces the chromosome number from diploid to haploid
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. © 2012 Pearson Education, Inc. 69

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. © 2012 Pearson Education, Inc. 70

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. © 2012 Pearson Education, Inc. 71

MEIOSIS I: Homologous chromosomes separate
Figure 8.13_left MEIOSIS I: Homologous chromosomes separate INTERPHASE: Chromosomes duplicate Prophase I Metaphase I Anaphase I Centrosomes (with centriole pairs) Spindle microtubules attached to a kinetochore Sister chromatids remain attached Sites of crossing over Centrioles Spindle Tetrad Figure 8.13_left The stages of meiosis: Interphase and Meiosis I Nuclear envelope Chromatin Sister chromatids Centromere (with a kinetochore) Metaphase plate Fragments of the nuclear envelope Homologous chromosomes separate 72

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. © 2012 Pearson Education, Inc. 74

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. © 2012 Pearson Education, Inc. 75

Figure 8.13_right MEIOSIS II: Sister chromatids separate Telophase II and Cytokinesis Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Figure 8.13_right The stages of meiosis: Telophase I and Meiosis II 76

Two lily cells undergo meiosis II Figure 8.13_5
Figure 8.13_5 Two lily cells undergo meiosis II Two lily cells undergo meiosis II 77

Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator. Meiosis II – Anaphase II Sister chromatids separate and chromosomes move toward opposite poles. © 2012 Pearson Education, Inc. 78

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. © 2012 Pearson Education, Inc. 79

8.14 Mitosis and meiosis have important similarities and differences
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. © 2012 Pearson Education, Inc. 80

(before chromosome duplication)
Figure 8.14 MITOSIS MEIOSIS I Parent cell (before chromosome duplication) Prophase Site of crossing over Prophase I Duplicated chromosome (two sister chromatids) Tetrad formed by synapsis of homologous chromosomes Chromosome duplication Chromosome duplication 2n  4 Metaphase Metaphase I Chromosomes align at the metaphase plate Tetrads (homologous pairs) align at the metaphase plate Anaphase Telophase Anaphase I Telophase I Homologous chromosomes separate during anaphase I; sister chromatids remain together Figure 8.14 Comparison of mitosis and meiosis Sister chromatids separate during anaphase Daughter cells of meiosis I Haploid n  2 MEIOSIS II 2n 2n No further chromosomal duplication; sister chromatids separate during anaphase II Daughter cells of mitosis n n n n Daughter cells of meiosis II 81

(before chromosome duplication)
Figure 8.14_1 MITOSIS MEIOSIS I Parent cell (before chromosome duplication) Prophase Prophase I Site of crossing over Chromosome duplication Chromosome duplication Tetrad 2n  4 Metaphase Metaphase I Figure 8.14_1 Comparison of mitosis and meiosis (part 1) Chromosomes align at the metaphase plate Tetrads (homologous pairs) align at the metaphase plate 82

Sister chromatids separate during anaphase
Figure 8.14_2 MITOSIS Metaphase Chromosomes align at the metaphase plate Anaphase Telophase Figure 8.14_2 Comparison of mitosis and meiosis (part 2) Sister chromatids separate during anaphase 2n 2n Daughter cells of mitosis 83

Daughter cells of meiosis II
Figure 8.14_3 MEIOSIS I Metaphase I Tetrads (homologous pairs) align at the metaphase plate Anaphase I Telophase I Homologous chromosomes separate during anaphase I; sister chromatids remain together Daughter cells of meiosis I Haploid n  2 Figure 8.14_3 Comparison of mitosis and meiosis (part 3) MEIOSIS II No further chromosomal duplication; sister chromatids separate during anaphase II n n n n Daughter cells of meiosis II 84

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Genetic variation in gametes results from independent orientation at metaphase I and random fertilization. © 2012 Pearson Education, Inc. 85

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring 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. © 2012 Pearson Education, Inc. 86

8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Random fertilization – The combination of each unique sperm with each unique egg increases genetic variability. © 2012 Pearson Education, Inc. 87

Two equally probable arrangements of chromosomes at metaphase I
Figure 8.15_s1 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Figure 8.15_s1 Results of the independent orientation of chromosomes at metaphase I (step 1) 88

Figure 8.15_s2 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 8.15_s2 Results of the independent orientation of chromosomes at metaphase I (step 2) 89

Figure 8.15_s3 Possibility A Possibility B Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 8.15_s3 Results of the independent orientation of chromosomes at metaphase I (step 3) Gametes Combination 1 Combination 2 Combination 3 Combination 4 90

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. © 2012 Pearson Education, Inc. 91

duplicated chromosomes)
Figure 8.16 Coat-color genes Eye-color genes C E Brown Black Brown coat (C); black eyes (E) C E C E Meiosis c e c Figure 8.16 Differing genetic information (coat color and eye color) on homologous chromosomes e c e White Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes White coat (c); pink eyes (e) 92

8.17 Crossing over further increases genetic variability
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. © 2012 Pearson Education, Inc. 93

Chiasma Tetrad Figure 8.17A
Figure 8.17A Chiasmata, the sites of crossing over 94

chromosomes in synapsis) c e
Figure 8.17B_1 C E Tetrad (pair of homologous chromosomes in synapsis) c e Breakage of homologous chromatids 1 C E c e Figure 8.17B_1 How crossing over leads to genetic recombination (part 1) Joining of homologous chromatids 2 C E Chiasma c e 95

Separation of homologous chromosomes at anaphase I
Figure 8.17B_2 C E Chiasma c e Separation of homologous chromosomes at anaphase I 3 C E Figure 8.17B_2 How crossing over leads to genetic recombination (part 2) C e c E c e 96

Separation of chromatids at anaphase II and completion of meiosis
Figure 8.17B_3 C E C e E c c e Separation of chromatids at anaphase II and completion of meiosis 4 C E Parental type of chromosome Figure 8.17B_3 How crossing over leads to genetic recombination (part 3) C e Recombinant chromosome c E Recombinant chromosome c e Parental type of chromosome Gametes of four genetic types 97

ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE

8.18 A karyotype is a photographic inventory of an individual’s chromosomes
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. © 2012 Pearson Education, Inc. 99

Centromere Sister chromatids Pair of homologous chromosomes
Figure 8.18_s5 Centromere Sister chromatids Pair of homologous chromosomes Figure 8.18_s5 Preparation of a karyotype from a blood sample (step 5) 5 Sex chromosomes 100

8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
Trisomy 21 involves the inheritance of three copies of chromosome 21 and is the most common human chromosome abnormality. © 2012 Pearson Education, Inc. 101

8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
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. © 2012 Pearson Education, Inc. 102

Figure 8.19A Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome Trisomy 21 103

Infants with Down syndrome
Figure 8.19B 90 80 70 60 50 Infants with Down syndrome (per 1,000 births) 40 30 Figure 8.19B Maternal age and incidence of Down syndrome 20 10 20 25 30 35 40 45 50 Age of mother 104

8.20 Accidents during meiosis can alter chromosome number
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. © 2012 Pearson Education, Inc. 105

MEIOSIS I Nondisjunction Figure 8.20A_s1
Figure 8.20A_s1 Nondisjunction in meiosis I (step 1) 106

MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Figure 8.20A_s2
Figure 8.20A_s2 Nondisjunction in meiosis I (step 2) 107

MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Gametes
Figure 8.20A_s3 MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Figure 8.20A_s3 Nondisjunction in meiosis I (step 3) Gametes Number of chromosomes n  1 n  1 n  1 n  1 Abnormal gametes 108

MEIOSIS I Normal meiosis I Figure 8.20B_s1
Figure 8.20B_s1 Nondisjunction in meiosis II (step 1) 109

MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction Figure 8.20B_s2
Figure 8.20B_s2 Nondisjunction in meiosis II (step 2) 110

MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction n  1 n  1 n n
Figure 8.20B_s3 MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction Figure 8.20B_s3 Nondisjunction in meiosis II (step 3) n  1 n  1 n n Abnormal gametes Normal gametes 111

8.21 CONNECTION: Abnormal numbers of sex chromosomes do not usually affect survival
Sex chromosome abnormalities tend to be less severe, perhaps because of the small size of the Y chromosome or X-chromosome inactivation. © 2012 Pearson Education, Inc. 112

8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
Chromosome breakage can lead to rearrangements that can produce genetic disorders or, if changes occur in somatic cells, cancer. © 2012 Pearson Education, Inc. 113

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. © 2012 Pearson Education, Inc. 114

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. © 2012 Pearson Education, Inc. 115

Reciprocal translocation
Figure 8.23A Deletion Inversion Duplication Reciprocal translocation Homologous chromosomes Nonhomologous chromosomes Figure 8.23A Alterations of chromosome structure 116

Activated cancer-causing gene
Figure 8.23B Chromosome 9 Reciprocal translocation Chromosome 22 Activated cancer-causing gene Figure 8.23B The translocation associated with chronic myelogenous leukemia “Philadelphia chromosome” 117

The Cellular Basis of Reproduction and Inheritance

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