Chapter 8 Cellular Reproduction Cells from Cells Power

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Chapter 8 Cellular Reproduction: Cells from Cells Power. Point® Lectures for Campbell Essential Biology,

Chapter 8 Cellular Reproduction: Cells from Cells Power. Point® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc.

WHAT CELL REPRODUCTION ACCOMPLISHES • Reproduction: – May result in the birth of new

WHAT CELL REPRODUCTION ACCOMPLISHES • Reproduction: – May result in the birth of new organisms – More commonly involves the production of new cells • When a cell undergoes reproduction, or cell division, two “daughter” cells are produced that are genetically identical to each other and to the “parent” cell. • Before a parent cell splits into two, it duplicates its chromosomes, the structures that contain most of the organism’s DNA. • During cell division, each daughter cell receives one set of chromosomes. © 2010 Pearson Education, Inc.

 • Cell division plays important roles in the lives of organisms. • Cell

• Cell division plays important roles in the lives of organisms. • Cell division: – Replaces damaged or lost cells – Permits growth – Allows for reproduction © 2010 Pearson Education, Inc.

Human kidney cell LM Colorized TEM FUNCTIONS OF CELL DIVISION Cell Replacement Growth via

Human kidney cell LM Colorized TEM FUNCTIONS OF CELL DIVISION Cell Replacement Growth via Cell Division Early human embryo Figure 8. 1 a

LM FUNCTIONS OF CELL DIVISION Asexual Reproduction Amoeba Sea stars African Violet Figure 8.

LM FUNCTIONS OF CELL DIVISION Asexual Reproduction Amoeba Sea stars African Violet Figure 8. 1 b

 • In asexual reproduction: – Single-celled organisms reproduce by simple cell division –

• In asexual reproduction: – Single-celled organisms reproduce by simple cell division – There is no fertilization of an egg by a sperm • Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces. • Growing a new plant from a clipping is another example of asexual reproduction. • In asexual reproduction, the lone parent and its offspring have identical genes. • Mitosis is the type of cell division responsible for: – Asexual reproduction – Growth and maintenance of multicellular organisms © 2010 Pearson Education, Inc.

 • Sexual reproduction requires fertilization of an egg by a sperm using a

• Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis. • Thus, sexually reproducing organisms use: – Meiosis for reproduction – Mitosis for growth and maintenance © 2010 Pearson Education, Inc.

THE CELL CYCLE AND MITOSIS • In a eukaryotic cell: – Most genes are

THE CELL CYCLE AND MITOSIS • In a eukaryotic cell: – Most genes are located on chromosomes in the cell nucleus – A few genes are found in DNA in mitochondria and chloroplasts © 2010 Pearson Education, Inc.

Eukaryotic Chromosomes • Each eukaryotic chromosome contains one very long DNA molecule, typically bearing

Eukaryotic Chromosomes • Each eukaryotic chromosome contains one very long DNA molecule, typically bearing thousands of genes. • The number of chromosomes in a eukaryotic cell depends on the species. © 2010 Pearson Education, Inc.

Species Indian muntjac deer Koala Opossum Giraffe Mouse Human Duck-billed platypus Buffalo Dog Red

Species Indian muntjac deer Koala Opossum Giraffe Mouse Human Duck-billed platypus Buffalo Dog Red viscacha rat Number of chromosomes in body cells 6 16 22 30 40 46 54 60 78 102 Figure 8. 2

 • Chromosomes: – Are made of chromatin, a combination of DNA and protein

• Chromosomes: – Are made of chromatin, a combination of DNA and protein molecules – Are not visible in a cell until cell division occurs © 2010 Pearson Education, Inc.

LM Chromosomes Figure 8. 3

LM Chromosomes Figure 8. 3

 • The DNA in a cell is packed into an elaborate, multilevel system

• The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding. • Histones are proteins used to package DNA in eukaryotes. • Nucleosomes consist of DNA wound around histone molecules. © 2010 Pearson Education, Inc.

DNA double helix Histones TEM “Beads on a string” Nucleosome Tight helical fiber Duplicated

DNA double helix Histones TEM “Beads on a string” Nucleosome Tight helical fiber Duplicated chromosomes (sister chromatids) TEM Looped domains Centromere Figure 8. 4

DNA double helix Histones TEM “Beads on a string” Nucleosome Figure 8. 4 a

DNA double helix Histones TEM “Beads on a string” Nucleosome Figure 8. 4 a

Tight helical fiber Looped domains TEM Duplicated chromosomes (sister chromatids) Centromere Figure 8. 4

Tight helical fiber Looped domains TEM Duplicated chromosomes (sister chromatids) Centromere Figure 8. 4 b

 • Before a cell divides, it duplicates all of its chromosomes, resulting in

• Before a cell divides, it duplicates all of its chromosomes, resulting in two copies called sister chromatids. • Sister chromatids are joined together at a narrow “waist” called the centromere. • When the cell divides, the sister chromatids separate from each other. • Once separated, each chromatid is: – Considered a full-fledged chromosome – Identical to the original chromosome © 2010 Pearson Education, Inc.

Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8. 5

Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8. 5

The Cell Cycle • A cell cycle is the orderly sequence of events that

The Cell Cycle • A cell cycle is the orderly sequence of events that extend from the time a cell is first formed from a dividing parent cell to its own division into two cells. • The cell cycle consists of two distinct phases: – Interphase – The mitotic phase © 2010 Pearson Education, Inc.

 • Most of a cell cycle is spent in interphase. • During interphase,

• Most of a cell cycle is spent in interphase. • During interphase, a cell: – Performs its normal functions – Doubles everything in its cytoplasm – Grows in size Video: Animal Mitosis © 2010 Pearson Education, Inc.

INTERPHASE Centrosomes (with centriole pairs) Chromatin PROPHASE Fragments of Early mitotic Centrosome nuclear envelope

INTERPHASE Centrosomes (with centriole pairs) Chromatin PROPHASE Fragments of Early mitotic Centrosome nuclear envelope spindle Centromere Spindle microtubules LM Chromosome, consisting Nuclear Plasma envelope membrane of two sister chromatids Figure 8. 7. a

INTERPHASE Centrosomes (with centriole pairs) Chromatin PROPHASE Fragments of Early mitotic Centrosome nuclear envelope

INTERPHASE Centrosomes (with centriole pairs) Chromatin PROPHASE Fragments of Early mitotic Centrosome nuclear envelope spindle Nuclear Plasma envelope membrane Chromosome, consisting of two sister chromatids Centromere Spindle microtubules Figure 8. 7. aa

LM INTERPHASE Figure 8. 7. ab

LM INTERPHASE Figure 8. 7. ab

LM PROPHASE Figure 8. 7. ac

LM PROPHASE Figure 8. 7. ac

LM PROPHASE Figure 8. 7. ad

LM PROPHASE Figure 8. 7. ad

 • The mitotic (M) phase includes two overlapping processes: – Mitosis, in which

• The mitotic (M) phase includes two overlapping processes: – Mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei – Cytokinesis, in which the cytoplasm is divided in two © 2010 Pearson Education, Inc.

S phase (DNA synthesis; chromosome duplication) Interphase: metabolism and growth (90% of time) G

S phase (DNA synthesis; chromosome duplication) Interphase: metabolism and growth (90% of time) G 1 G 2 Mitotic (M) phase: cell division (10% of time) Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) Figure 8. 6

Mitosis and Cytokinesis • During mitosis the mitotic spindle, a football-shaped structure of microtubules,

Mitosis and Cytokinesis • During mitosis the mitotic spindle, a football-shaped structure of microtubules, guides the separation of two sets of daughter chromosomes. • Spindle microtubules grow from two centrosomes, clouds of cytoplasmic material that in animal cells contain centrioles. • Mitosis consists of four distinct phases: – (A) Prophase © 2010 Pearson Education, Inc.

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Nuclear envelope forming Spindle Cleavage furrow Daughter chromosomes Figure

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Nuclear envelope forming Spindle Cleavage furrow Daughter chromosomes Figure 8. 7 b

– (A) Prophase – (B) Metaphase – (C) Anaphase – (D) Telophase © 2010

– (A) Prophase – (B) Metaphase – (C) Anaphase – (D) Telophase © 2010 Pearson Education, Inc.

 • Cytokinesis typically: – Occurs during telophase – Divides the cytoplasm – Is

• Cytokinesis typically: – Occurs during telophase – Divides the cytoplasm – Is different in plant and animal cells © 2010 Pearson Education, Inc.

SEM Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8. 8 a

SEM Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8. 8 a

SEM Cleavage furrow Figure 8. 8 aa

SEM Cleavage furrow Figure 8. 8 aa

Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8. 8 ab

Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8. 8 ab

Cell plate Daughter forming nucleus LM Wall of parent cell Cell wall Vesicles containing

Cell plate Daughter forming nucleus LM Wall of parent cell Cell wall Vesicles containing Cell plate cell wall material New cell wall Daughter cells Figure 8. 8 b

Cell plate forming Daughter nucleus LM Wall of parent cell Figure 8. 8 ba

Cell plate forming Daughter nucleus LM Wall of parent cell Figure 8. 8 ba

Cell wall Vesicles containing cell wall material Cell plate New cell wall Daughter cells

Cell wall Vesicles containing cell wall material Cell plate New cell wall Daughter cells Figure 8. 8 bb

Cancer Cells: Growing Out of Control • Normal plant and animal cells have a

Cancer Cells: Growing Out of Control • Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send “stop” and “goahead” signals at certain key points during the cell cycle. What Is Cancer? • Cancer is a disease of the cell cycle. • Cancer cells do not respond normally to the cell cycle control system. © 2010 Pearson Education, Inc.

 • Cancer cells can form tumors, abnormally growing masses of body cells. •

• Cancer cells can form tumors, abnormally growing masses of body cells. • The spread of cancer cells beyond their original site of origin is metastasis. • Malignant tumors can: – Spread to other parts of the body – Interrupt normal body functions • A person with a malignant tumor is said to have cancer. © 2010 Pearson Education, Inc.

Lymph vessels Tumor Blood vessel Glandular tissue A tumor grows from a single cancer

Lymph vessels Tumor Blood vessel Glandular tissue A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Metastasis: Cancer cells spread through lymph and blood vessels to other parts of the body. Figure 8. 9

Cancer Treatment • Cancer treatment can involve: – Radiation therapy, which damages DNA and

Cancer Treatment • Cancer treatment can involve: – Radiation therapy, which damages DNA and disrupts cell division – Chemotherapy, which uses drugs that disrupt cell division © 2010 Pearson Education, Inc.

Cancer Prevention and Survival • Certain behaviors can decrease the risk of cancer: –

Cancer Prevention and Survival • Certain behaviors can decrease the risk of cancer: – Not smoking – Exercising adequately – Avoiding exposure to the sun – Eating a high-fiber, low-fat diet – Performing self-exams – Regularly visiting a doctor to identify tumors early © 2010 Pearson Education, Inc.

Meiosis, the Basis of Sexual Reproduction • Sexual reproduction: – Uses meiosis – Uses

Meiosis, the Basis of Sexual Reproduction • Sexual reproduction: – Uses meiosis – Uses fertilization – Produces offspring that contain a unique combination of genes from the parents © 2010 Pearson Education, Inc.

Figure 8. 10

Figure 8. 10

Homologous Chromosomes • Different individuals of a single species have the same number and

Homologous Chromosomes • Different individuals of a single species have the same number and types of chromosomes. • A human somatic cell: – Is a typical body cell – Has 46 chromosomes • A karyotype is an image that reveals an orderly arrangement of chromosomes. • Homologous chromosomes are matching pairs of chromosomes that can possess different versions of the same genes. © 2010 Pearson Education, Inc.

LM Pair of homologous chromosomes Centromere Sister chromatids One duplicated chromosome Figure 8. 11

LM Pair of homologous chromosomes Centromere Sister chromatids One duplicated chromosome Figure 8. 11

 • Humans have: – Two different sex chromosomes, X and Y – Twenty-two

• Humans have: – Two different sex chromosomes, X and Y – Twenty-two pairs of matching chromosomes, called autosomes © 2010 Pearson Education, Inc.

Gametes and the Life Cycle of a Sexual Organism • The life cycle of

Gametes and the Life Cycle of a Sexual Organism • The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next. © 2010 Pearson Education, Inc.

Haploid gametes (n 23) Egg cell n n Sperm cell FERTILIZATION MEIOSIS Multicellular diploid

Haploid gametes (n 23) Egg cell n n Sperm cell FERTILIZATION MEIOSIS Multicellular diploid adults (2 n 46) 2 n MITOSIS and development Diploid zygote (2 n 46) Key Haploid (n) Diploid (2 n) Figure 8. 12

 • Humans are diploid organisms in which: – Their somatic cells contain two

• Humans are diploid organisms in which: – Their somatic cells contain two sets of chromosomes – Their gametes are haploid, having only one set of chromosomes • In humans, a haploid sperm fuses with a haploid egg during fertilization to form a diploid zygote. • Sexual life cycles involve an alternation of diploid and haploid stages. • Meiosis produces haploid gametes, which keeps the chromosome number from doubling every generation. © 2010 Pearson Education, Inc.

Chromosomes duplicate. Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous

Chromosomes duplicate. Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes Sister chromatids INTERPHASE BEFORE MEIOSIS Figure 8. 13 -1

Chromosomes duplicate. Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous

Chromosomes duplicate. Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes INTERPHASE BEFORE MEIOSIS Homologous chromosomes separate. Sister chromatids MEIOSIS I Figure 8. 13 -2

Chromosomes duplicate. Homologous chromosomes separate. Sister chromatids separate. Pair of homologous chromosomes in diploid

Chromosomes duplicate. Homologous chromosomes separate. Sister chromatids separate. Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes INTERPHASE BEFORE MEIOSIS Sister chromatids MEIOSIS II Figure 8. 13 -3

The Process of Meiosis • In meiosis: – Haploid daughter cells are produced in

The Process of Meiosis • In meiosis: – Haploid daughter cells are produced in diploid organisms – Interphase is followed by two consecutive divisions, meiosis I and meiosis II – Crossing over occurs © 2010 Pearson Education, Inc.

MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE INTERPHASE Centrosomes (with centriole pairs) Nuclear envelope Chromatin Chromosomes

MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE INTERPHASE Centrosomes (with centriole pairs) Nuclear envelope Chromatin Chromosomes duplicate. PROPHASE I Sites of crossing over Spindle Sister chromatids Pair of homologous chromosomes Homologous chromosomes pair up and exchange segments. METAPHASE I Microtubules attached to chromosome ANAPHASE I Sister chromatids remain attached Centromere Pairs of homologous chromosomes line up. Pairs of homologous chromosomes split up. Figure 8. 14 a

INTERPHASE Centrosomes (with centriole pairs) Nuclear envelope Chromatin Figure 8. 14 aa

INTERPHASE Centrosomes (with centriole pairs) Nuclear envelope Chromatin Figure 8. 14 aa

PROPHASE I METAPHASE I Microtubules attached Sites of crossing over to chromosome Spindle ANAPHASE

PROPHASE I METAPHASE I Microtubules attached Sites of crossing over to chromosome Spindle ANAPHASE I Sister chromatids remain attached TELOPHASE I AND CYTOKINESIS Cleavage furrow Sister Centromere chromatids Pair of homologous chromosomes Figure 8. 14 ab

PROPHASE I METAPHASE I Microtubules attached to chromosome Sites of crossing over Spindle Sister

PROPHASE I METAPHASE I Microtubules attached to chromosome Sites of crossing over Spindle Sister chromatids Centromere Pair of homologous chromosomes Figure 8. 14 ac

ANAPHASE I Sister chromatids remain attached TELOPHASE I AND CYTOKINESIS Cleavage furrow TELOPHASE I

ANAPHASE I Sister chromatids remain attached TELOPHASE I AND CYTOKINESIS Cleavage furrow TELOPHASE I AND CYTOKINESIS Figure 8. 14 ad

MEIOSIS II: SISTER CHROMATIDS SEPARATE TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE

MEIOSIS II: SISTER CHROMATIDS SEPARATE TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Cleavage furrow Sister chromatids separate Two haploid cells form; chromosomes are still doubled. Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes. Figure 8. 14 b

PROPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells

PROPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells forming METAPHASE II Figure 8. 14 ba

PROPHASE II METAPHASE II Figure 8. 14 bb

PROPHASE II METAPHASE II Figure 8. 14 bb

LM Figure 8. 14 bc

LM Figure 8. 14 bc

ANAPHASE II Sister chromatids separate TELOPHASE II AND CYTOKINESIS Haploid daughter cells forming Figure

ANAPHASE II Sister chromatids separate TELOPHASE II AND CYTOKINESIS Haploid daughter cells forming Figure 8. 14 bd

Review: Comparing Mitosis and Meiosis • In mitosis and meiosis, the chromosomes duplicate only

Review: Comparing Mitosis and Meiosis • In mitosis and meiosis, the chromosomes duplicate only once, during the preceding interphase. © 2010 Pearson Education, Inc.

 • The number of cell divisions varies: – Mitosis uses one division and

• The number of cell divisions varies: – Mitosis uses one division and produces two diploid cells – Meiosis uses two divisions and produces four haploid cells • All the events unique to meiosis occur during meiosis I. © 2010 Pearson Education, Inc.

MEIOSIS MITOSIS Prophase I Prophase Chromosome duplication Duplicated chromosome (two sister chromatids) MEIOSIS I

MEIOSIS MITOSIS Prophase I Prophase Chromosome duplication Duplicated chromosome (two sister chromatids) MEIOSIS I Chromosome duplication Parent cell (before chromosome duplication) 2 n 4 Homologous chromosomes come together in pairs. Site of crossing over between homologous (nonsister) chromatids Metaphase I Metaphase Homologous pairs align at the middle of the cell. Chromosomes align at the middle of the cell. Anaphase I Telophase I Anaphase Telophase 2 n Sister chromatids separate during anaphase. Daughter cells of mitosis 2 n Homologous chromosomes separate during anaphase I; sister chromatids remain together. Chromosome with two sister chromatids Haploid n 2 Daughter cells of meiosis I MEIOSIS II Sister chromatids separate during anaphase II. n n n Daughter cells of meiosis II n Figure 8. 15

MITOSIS MEIOSIS Prophase I Prophase Chromosome duplication Duplicated chromosome (two sister chromatids) Chromosome duplication

MITOSIS MEIOSIS Prophase I Prophase Chromosome duplication Duplicated chromosome (two sister chromatids) Chromosome duplication Parent cell (before chromosome duplication) 2 n 4 Homologous chromosomes come together in pairs. Metaphase MEIOSIS I Site of crossing over between homologous (nonsister) chromatids Metaphase I Chromosomes align at the middle of the cell. Homologous pairs align at the middle of the cell. Figure 8. 15 a

Anaphase I Telophase I Anaphase Telophase 2 n Sister chromatids separate during anaphase. Daughter

Anaphase I Telophase I Anaphase Telophase 2 n Sister chromatids separate during anaphase. Daughter cells of mitosis 2 n Homologous chromosomes separate during anaphase I; sister chromatids remain together. Chromosome with two sister chromatids Haploid n 2 Daughter cells of meiosis I MEIOSIS II Sister chromatids separate during anaphase II. n n n Daughter cells of meiosis II n Figure 8. 15 b

The Origins of Genetic Variation • Offspring of sexual reproduction are genetically different from

The Origins of Genetic Variation • Offspring of sexual reproduction are genetically different from their parents and one another. © 2010 Pearson Education, Inc.

Independent Assortment of Chromosomes • When aligned during metaphase I of meiosis, the side-by-side

Independent Assortment of Chromosomes • When aligned during metaphase I of meiosis, the side-by-side orientation of each homologous pair of chromosomes is a matter of chance. • Every chromosome pair orients independently of the others during meiosis. © 2010 Pearson Education, Inc.

 • For any species the total number of chromosome combinations that can appear

• For any species the total number of chromosome combinations that can appear in the gametes due to independent assortment is: – 2 n where n is the haploid number. • For a human: – n = 23 – 223 = 8, 388, 608 different chromosome combinations possible in a gamete Animation: Genetic Variation Blast Animation: Genetic Variation: Independent Assortment © 2010 Pearson Education, Inc.

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis I Figure 8. 16 -1

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis I Figure 8. 16 -1

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis II Figure 8. 16 -2

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis II Figure 8. 16 -2

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis II Gametes Combination a Combination b Combination

POSSIBILITY 2 POSSIBILITY 1 Metaphase of meiosis II Gametes Combination a Combination b Combination c Combination d Figure 8. 16 -3

Random Fertilization • A human egg cell is fertilized randomly by one sperm, leading

Random Fertilization • A human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote. • If each gamete represents one of 8, 388, 608 different chromosome combinations, at fertilization, humans would have 8, 388, 608 × 8, 388, 608, or more than 70 trillion, different possible chromosome combinations. © 2010 Pearson Education, Inc.

Figure 8. 17

Figure 8. 17

Crossing Over • In crossing over: – Homologous chromosomes exchange genetic information – Genetic

Crossing Over • In crossing over: – Homologous chromosomes exchange genetic information – Genetic recombination, the production of gene combinations different from those carried by parental chromosomes, occurs © 2010 Pearson Education, Inc.

Prophase I of meiosis Duplicated pair of homologous chromosomes Figure 8. 18 -1

Prophase I of meiosis Duplicated pair of homologous chromosomes Figure 8. 18 -1

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes Chiasma, site of crossing over Figure 8. 18 -2

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes Chiasma, site of crossing over Metaphase I Sister chromatids remain joined at their centromeres. Spindle microtubule Figure 8. 18 -3

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes Chiasma, site of crossing over Metaphase I Sister chromatids remain joined at their centromeres. Spindle microtubule Metaphase II Figure 8. 18 -4

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes

Prophase I of meiosis Homologous chromatids exchange corresponding segments. Duplicated pair of homologous chromosomes Chiasma, site of crossing over Metaphase I Sister chromatids remain joined at their centromeres. Spindle microtubule Metaphase II Gametes Recombinant chromosomes combine genetic information from different parents. Recombinant chromosomes Figure 8. 18 -5

When Meiosis Goes Awry • What happens when errors occur in meiosis? • Such

When Meiosis Goes Awry • What happens when errors occur in meiosis? • Such mistakes can result in genetic abnormalities that range from mild to fatal. © 2010 Pearson Education, Inc.

How Accidents during Meiosis Can Alter Chromosome Number • In nondisjunction, the members of

How Accidents during Meiosis Can Alter Chromosome Number • In nondisjunction, the members of a chromosome pair fail to separate during anaphase, producing gametes with an incorrect number of chromosomes. • Nondisjunction can occur during meiosis I or II. © 2010 Pearson Education, Inc.

NONDISJUNCTION IN MEIOSIS II Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate.

NONDISJUNCTION IN MEIOSIS II Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate. Figure 8. 20 -1

NONDISJUNCTION IN MEIOSIS II NONDISJUNCTION IN MEIOSIS I Meiosis I Nondisjunction: Pair of homologous

NONDISJUNCTION IN MEIOSIS II NONDISJUNCTION IN MEIOSIS I Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate. Meiosis II Nondisjunction: Pair of sister chromatids fails to separate. Figure 8. 20 -2

NONDISJUNCTION IN MEIOSIS II NONDISJUNCTION IN MEIOSIS I Meiosis I Nondisjunction: Pair of homologous

NONDISJUNCTION IN MEIOSIS II NONDISJUNCTION IN MEIOSIS I Meiosis I Nondisjunction: Pair of homologous chromosomes fails to separate. Meiosis II Nondisjunction: Pair of sister chromatids fails to separate. Gametes n 1 n– 1 Abnormal gametes Number of n – 1 chromosomes n 1 n– 1 Abnormal gametes n n Normal gametes Figure 8. 20 -3

 • If nondisjunction occurs, and a normal sperm fertilizes an egg with an

• If nondisjunction occurs, and a normal sperm fertilizes an egg with an extra chromosome, the result is a zygote with a total of 2 n + 1 chromosomes. • If the organism survives, it will have an abnormal number of genes. © 2010 Pearson Education, Inc.

Abnormal egg cell with extra chromosome n 1 Normal sperm cell n (normal) Abnormal

Abnormal egg cell with extra chromosome n 1 Normal sperm cell n (normal) Abnormal zygote with extra chromosome 2 n 1 Figure 8. 21

Down Syndrome: An Extra Chromosome 21 • Down Syndrome: – Is also called trisomy

Down Syndrome: An Extra Chromosome 21 • Down Syndrome: – Is also called trisomy 21 – Is a condition in which an individual has an extra chromosome 21 – Affects about one out of every 700 children • The incidence of Down Syndrome increases with the age of the mother. © 2010 Pearson Education, Inc.

LM Chromosome 21 Figure 8. 22

LM Chromosome 21 Figure 8. 22

Infants with Down syndrome (per 1, 000 births) 90 80 70 60 50 40

Infants with Down syndrome (per 1, 000 births) 90 80 70 60 50 40 30 20 10 0 20 25 30 35 40 45 50 Age of mother Figure 8. 23

Abnormal Numbers of Sex Chromosomes • Nondisjunction can also affect the sex chromosomes. ©

Abnormal Numbers of Sex Chromosomes • Nondisjunction can also affect the sex chromosomes. © 2010 Pearson Education, Inc.

Table 8. 1

Table 8. 1

Evolution Connection: The Advantages of Sex • Asexual reproduction conveys an evolutionary advantage when

Evolution Connection: The Advantages of Sex • Asexual reproduction conveys an evolutionary advantage when plants are: – Sparsely distributed – Superbly suited to a stable environment © 2010 Pearson Education, Inc.

Figure 8. 24

Figure 8. 24

 • Sexual reproduction may convey an evolutionary advantage by: – Speeding adaptation to

• Sexual reproduction may convey an evolutionary advantage by: – Speeding adaptation to a changing environment – Allowing a population to more easily rid itself of harmful genes © 2010 Pearson Education, Inc.

Duplication of all chromosomes Distribution via mitosis Genetically identical daughter cells Figure 8. UN

Duplication of all chromosomes Distribution via mitosis Genetically identical daughter cells Figure 8. UN 1

Chromosome (one long piece of DNA) Centromere Sister chromatids Duplicated chromosome Figure 8. UN

Chromosome (one long piece of DNA) Centromere Sister chromatids Duplicated chromosome Figure 8. UN 2

S phase DNA synthesis; chromosome duplication Interphase Cell growth and chromosome duplication G 2

S phase DNA synthesis; chromosome duplication Interphase Cell growth and chromosome duplication G 2 G 1 Mitotic (M) phase Genetically identical “daughter” cells Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) Figure 8. UN 3

Human Life Cycle Haploid gametes (n 23) Key Haploid (n) n Egg cell Diploid

Human Life Cycle Haploid gametes (n 23) Key Haploid (n) n Egg cell Diploid (2 n) n Sperm cell MEIOSIS FERTILIZATION Male and female diploid adults (2 n 46) Diploid zygote (2 n 46) MITOSIS and development 2 n Figure 8. UN 4

MEIOSIS MITOSIS Parent cell (2 n) Chromosome duplication MEIOSIS I Pairing of homologous chromosome

MEIOSIS MITOSIS Parent cell (2 n) Chromosome duplication MEIOSIS I Pairing of homologous chromosome Crossing over 2 n Daughter cells 2 n MEIOSIS II n n Daughter cells Figure 8. UN 5

LM (b) (a) (c) (d) Figure 8. UN 6

LM (b) (a) (c) (d) Figure 8. UN 6