Chapter 8 Cellular Reproduction Cells from Cells Power

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 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 division: – Replaces damaged or lost cells – Permits growth – Allows for reproduction © 2010 Pearson Education, Inc.

• 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 special type of cell division called meiosis. • Thus, sexually reproducing organisms use: – Meiosis for reproduction – Mitosis for growth and maintenance • 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 • 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 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 molecules – Are not visible in a cell until cell division occurs © 2010 Pearson Education, Inc.

• 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. • 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. © 2010 Pearson Education, Inc.

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 b

• 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 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 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 • 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 © 2010 Pearson Education, Inc.

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

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, 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. © 2010 Pearson Education, Inc.

Cell Cycle, Mitosis and Meiosis §http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animation __control_of_the_cell_cycle. html §http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animation __how_the_cell_cycle_works. html §http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animation __mitosis_and_cytokinesis. html §http: //highered. mcgrawhill. com/sites/0072495855/student_view 0/chapter 2/animation __comparison_of_meiosis_and_mitosis__quiz_1_. html © 2010 Pearson Education, Inc.

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

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

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 “go-ahead” signals at certain key points during the cell cycle. • Cancer is a disease of the cell cycle. • Cancer cells do not respond normally to the cell cycle control system. • 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. • 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.

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 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.

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.

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

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. 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 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.

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

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 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 their parents and one another. • 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. • 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 © 2010 Pearson Education, Inc.

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 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.

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 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 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 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 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 mistakes can result in genetic abnormalities that range from mild to fatal. • 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. • 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.

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 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 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

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 21 – Is a condition in which an individual has an extra chromosome 21 – Affects about one out of every 700 children © 2010 Pearson Education, Inc.

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

• Nondisjunction can also affect the sex chromosomes. Table 8. 1

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

These are two mammograms—the on the left is normal and the on the right indicates a tumor. Genetic tests are now available to screen for women with a high genetic risk for developing breast cancer. Some women in this situation have opted for a radical mastectomy before the appearance of a tumor. As a doctor, would you consider advising your patient in this manner? Strongly Agree A. © 2010 Pearson Education, Inc. B. C. D. E. Strongly Disagree

One of the first human cell lines to survive indefinitely was derived from a cancer patient who died in 1951. Known as the He. La line for Henrietta Lacks, the cell line continues today in laboratories throughout the world and is even available for high school classrooms to study karyotyping. In 1951 people didn’t fully realize the potential applications of unique cells or DNA. Do you think that a patient should retain all rights to his or her cells or DNA during medical procedures? Strongly Agree A. © 2010 Pearson Education, Inc. B. C. D. E. Strongly Disagree