Campbell Biology 9th Ed Ch 8 PDF

# The Cellular Basis of Reproduction and Inheritance ## Can cancer therapy be personalized? - DCIS, ductal carcinoma in situ, also called stage 0 breast cancer, is a type of breast cancer where cancerous cells have not spread beyond the milk ducts. - DCIS can be treated with lumpectomy, mastectomy...

# The Cellular Basis of Reproduction and Inheritance ## Can cancer therapy be personalized? - DCIS, ductal carcinoma in situ, also called stage 0 breast cancer, is a type of breast cancer where cancerous cells have not spread beyond the milk ducts. - DCIS can be treated with lumpectomy, mastectomy, and radiation therapy - Cancer cells lose the ability to regulate their division. - Mammograms detect roughly 60,000 cases of DCIS in the United States each year. ## BIG IDEAS - **Cell Division and Reproduction:** Cell division is a key step in many of life's important processes. - **The Eukaryotic Cell Cycle and Mitosis:** Cells produce genetic duplicates through an ordered, tightly controlled process. - **Meiosis and Crossing Over:** The process of meiosis produces genetically varied haploid gametes from diploid cells. - **Alterations of Chromosome Number and Structure:** Errors in cell division can produce organisms with abnormal numbers of chromosomes. ## 8.1 Cell Division Plays Many Important Roles in the Lives of Organisms - The ability to transmit information is essential for reproduction. - **Asexual Reproduction:** The creation of genetically identical offspring by a single parent, without the participation of sperm and egg. - Examples: single-celled organisms, yeast, sea stars, and house plants. - **Sexual Reproduction:** Requires the fusion of gametes, egg, and sperm. - Produces genetically varied offspring. - Cell division plays critical roles in multicellular organisms: - **Growth:** Enables organisms to develop from a single cell (fertilized egg) into an adult organism. - **Renewal and Repair:** Replaces cells that die from normal wear and tear or from injuries. ## 8.2 Prokaryotes Reproduce by Binary Fission - Prokaryotes (single-celled bacteria and archaea) reproduce by binary fission - Most genes in prokaryotes are carried on one circular DNA molecule, which constitutes the organism's single chromosome. - The steps of binary fission: 1. Duplication of the chromosome and separation of the copies 2. Continued elongation of the cell and movement of the copies 3. Division into two daughter cells ## 8.3 The Large, Complex Chromosomes of Eukaryotes Duplicate With Each Cell Division - Eukaryotic cells generally have more genes, larger size, and more complex chromosomes than prokaryotic cells. - Human cells carry just under 21,000 genes, versus about 3,000 for a typical bacterium. - **Chromosomes:** Eukaryotic genes are found within the cell nucleus in multiple chromosomes. - Each species has a characteristic number of chromosomes in each cell nucleus. - **Chromatin:** Consists of one long DNA molecule, thousands of genes, and protein molecules. - The proteins help maintain the chromosome's structure and control the activity of its genes. - **Sister Chromatids:** Two copies of the original chromosome, are joined together along their lengths by proteins, most closely at the centromere. - During cell division, the sister chromatids separate from each other and go to different daughter cells, resulting in two daughter cells with a complete and identical set of chromosomes. ## 8.4 The Cell Cycle Includes Growth and Division Phases - **Cell Cycle:** Includes two main stages: 1. **Interphase:** Growing stage where the cell approximately doubles everything in its cytoplasm and replicates its DNA. - Subphases: - G1 phase ("first gap") - S phase ("synthesis" of DNA-also known as DNA replication) - G2 phase ("second gap") 2. **Mitotic Phase (M Phase):** Where the nucleus and its contents divide. - Includes: - **Mitosis:** The nucleus and its contents divide. - **Cytokinesis:** The cytoplasm is divided. ## 8.5 Cell Division is a Continuum of Dynamic Changes - **Mitosis:** A continuous process, described in five main stages: 1. **Prophase:** Chromatin condenses into discrete chromosomes, and the mitotic spindle begins to form. 2. **Prometaphase:** The nuclear envelope breaks into fragments, and microtubules extend into the nuclear region, reaching the chromosomes. 3. **Metaphase:** Duplicated chromosomes line up at the metaphase plate—an imaginary plane equidistant between the two poles of the spindle. 4. **Anaphase:** The two centromeres of each chromosome come apart. 5. **Telophase:** The chromosomes arrive at the poles of the cell; nuclear envelope form, mitotic spindle disappears, and the cytoplasm starts to divide. - **Cytokinesis:** Usually occurs simultaneously with telophase in animal cells as a cleavage furrow pinches the parent cell in two daughter cells. ## 8.6 Cytokinesis Differs for Plant and Animal Cells - **Cleavage:** In animal cells, cytokinesis occurs by cleavage. A shallow groove, a cleavage furrow, is formed, and the cytoplasm has a ring of microfilaments made of actin, associated with molecules of myosin, that contracts and pinches the parent cell in two. - **Cell Plate Formation:** In plant cells, a cell plate forms at the middle of the parent cell, from membranous vesicles containing cell wall material. The cell plate grows outward, accumulating more material, and the membrane of the cell plate fuses with the plasma membrane to form two daughter cells, each bounded by its own plasma membrane and cell wall. ## 8.7 The Rate of Cell Division is Affected by Environmental Factors - **Anchorage Dependence:** Most animal cells must be in contact with a solid surface to divide. - **Density-Dependent Inhibition:** Crowded cells stop dividing. This is caused by physical contact between cells. - **Growth Factors:** Most types of mammalian cells will divide only if certain proteins, called growth factors, are present. - For example, vascular endothelial growth factor (VEGF) stimulates the growth of new blood vessels during fetal development and after injury. ## 8.8 Growth Factors Signal the Cell Cycle Control System - The cell cycle control system directs the sequential events of the cell cycle. - **Checkpoints:** Critical control points (G1, G2, and M) where stop and go-ahead signals regulate the cycle. - The default setting is for the cell cycle to halt at these checkpoints unless overridden by go-ahead signals in the form of growth factors. - **Go Phase:** Cells in the Go phase are in a permanently non-dividing state. - **Growth Factors:** Can affect the cell cycle control system. - **Signal Transduction Pathways:** When a growth factor binds to a receptor protein in the plasma membrane, this triggers a series of protein molecules that convey a message to the cell cycle control system. ## 8.9 Growing Out of Control, Cancer Cells Produce Malignant Tumors - **Cancer:** A disease of the cell cycle where cells ignore normal signals that regulate the cell cycle. - Divide excessively and invade other tissues of the body, and can spread to other parts of the body (metastasis). - **Tumor:** Cancer cells may multiply to form a tumor - **Benign Tumor:** A mass of abnormally growing cells that remain at their original site. - **Malignant Tumor:** A mass of abnormally reproducing cells that can spread into neighboring tissues to invade other parts of the body. - **Metastasis:** The spread of cancer cells beyond their original site. - Cancer cells: - Do not heed normal signals that regulate the cell cycle. - Divide continuously at random points in the cell cycle, and often synthesize their own gowth factors. - Are often “immortal”, meaning they can go on dividing indefinitely. ## 8.10 The Best Cancer Treatment May Vary by Individual - **Oncologists:** Doctors who treat cancer. - Cancer therapy is shifting from “one-size-fits-all” models to personalized treatments. - **Observational Studies:** A common type of study for cancer patients. - Examples: studying the 20-year survival of 108,000 American women with DCIS. Results indicate a lower risk of death than initially thought, with higher risks for women under 40 or black. - **Controlled Studies:** More definitive but more difficult to undertake than observational studies. ## Meiosis and Crossing Over ## 8.11 Chromosomes Are Matched in Homologous Pairs - **Somatic Cells:** Contain paired chromosomes, one from each parent. - Humans have 46 chromosomes, 23 sets of homologous pairs. - **Homologous Chromosomes:** Chromosomes in a matching pair with the same genes at corresponding loci (locations). ## 8.12 Gametes Have a Single Set of Chromosomes - **Gametes:** Haploid cells contain only one set of chromosomes. - Humans: Gametes contain 23 chromosomes. - **Diploid Cells:** Contain two sets of homologous chromosomes. - Humans: Somatic cells contain 46 chromosomes. - **Sexual Life Cycle:** Alternates between haploid and diploid stages and includes: - Meiosis: Produces haploid gametes from diploid cells. - Fertilization: Fuses haploid gametes into a diploid zygote. ## 8.13 Meiosis Reduces The Chromosome Number From Diploid To Haploid - **Meiosis:** A process of two consecutive cell divisions that produce haploid gametes from diploid cells. - **Meiosis I:** - **Interphase:** Duplication of chromosomes. - **Prophase I:** Homologous chromosomes pair up, and crossing over occurs. - **Metaphase I:** Homologous chromosomes line up at the metaphase plate. - **Anaphase I:** Homologous chromosomes separate, migrating toward opposite poles of the cell. - **Telophase I:** Chromosomes arrive at the poles of the cell. Cytokinesis occurs, and two haploid daughter cells are produced. - **Meiosis II:** - **Prophase II:** Similar to mitosis. Spindle forms. - **Metaphase II:** Chromosomes line up at the metaphase plate. - **Anaphase II:** Sister chromatids, now individual chromosomes, separate, migrating toward opposite poles of the cell. - **Telophase II:** Nuclei form at the poles, and cytokinesis occurs, resulting in four haploid daughter cells. ## 8.14 Mitosis and Meiosis Have Important Similarities and Differences - **Similarities:** Both processes are preceded by chromosome duplication and involve the formation of spindle microtubules for chromosome movement. - **Differences:** - **Mitosis:** Produces two genetically identical diploid cells, used for growth, tissue repair, and asexual reproduction. - **Meiosis:** Produces four genetically unique haploid cells, used for sexual reproduction. ## 8.15 Independent Orientation of Chromosomes in Meiosis and Random Fertilization Lead To Varied Offspring - **Independent Assortment:** The orientation of homologous chromosomes at metaphase I is random, creating a diverse set of combinations in the resulting gametes. - **Random Fertilization:** The fusion of a sperm cell with an egg cell is a random event, further increasing the variability of offspring. ## 8.16 Homologous Chromosomes May Carry Different Versions of Genes - **Genes:** Units of information that specify inherited traits. - **Alleles:** Different versions of a gene. - For example, the gene for coat color may have alleles for brown fur (C) and white fur (c), or for black eyes (E) and pink eyes (e). - **Crossing Over:** The exchange of corresponding segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis. - Results in new combinations of genes, called recombinant chromosomes. ## 8.17 Crossing Over Further Increases Genetic Variability - **Recombinant Chromosomes:** Result from crossing over; they have new combinations of genes from the two parents. - **Importance:** Crossing over is essential for genetic diversity in sexually reproducing organisms and is the main driver of evolutionary change. ## Alterations of Chromosome Number and Structure ## 8.18 Accidents During Meiosis Can Alter Chromosome Number - **Nondisjunction:** Results from the failure of homologous chromosomes to separate during meiosis I or sister chromatids to separate during meiosis II. - **Consequences:** Some gametes have an extra chromosome, some lack a chromosome, and some have a normal complement. - Resulting zygote will have an abnormal number of chromosomes in all cells. ## 8.19 A Karyotype is a Photographic Inventory of An Individual's Chromosomes - **Karyotype:** An ordered display of magnified images of an individual's chromosomes arranged in pairs. - **Creating a Karyotype:** 1. Treat lymphocytes (white blood cells) with a chemical that stimulates mitosis. 2. Arrest mitosis at metaphase. 3. Stain the chromosomes. 4. Photograph and arrange the chromosomes into pairs according to size and shape. - **Sex Chromosomes:** Those that determine an individuals sex. - Humans: X and Y chromosomes. - **Autosome:** Any other chromosome other than a sex chromosome. ## 8.20 An Extra Copy of Chromosome 21 Causes Down Syndrome - **Trisomy 21:** A condition characterized by the presence of three copies of chromosome 21 in each cell. - **Down Syndrome:** A syndrome caused by trisomy 21. - Characterized by a variety of symptoms, including short stature, a flattened nose bridge, and mental delays. Individuals typically have a shorter-than-normal life span. - **Incidence of Down Syndrome:** - Affects about one in 850 children. - The risk of having a child with Down syndrome increases with the mother's age. ## 8.21 Abnormal Numbers of Sex Chromosomes Do Not Usually Affect Survival - **Abnormal Number of Sex Chromosomes:** Can occur due to nondisjunction. - **Klinefelter Syndrome:** Individuals with an extra X chromosome (XXY) are male. Often have abnormally small testes, are usually sterile, may have subnormal intelligence, and may have female body characteristics. - **Turner Syndrome:** Individuals with only one X chromosome (XO) are female. Often have short stature, a web of skin extending between the neck and shoulders, and sterile sex organs. - **XXY Syndrome:** Individuals with two Y chromosomes (XYY) are male. Often have normal intelligence, are fertile but are typically taller than average. - **XXX Syndrome:** Individuals with three X chromosomes (XXX) are female. Often have normal intelligence, are fertile and are typically taller than average. ## 8.22 New Species Can Arise From Errors In Cell Division - **Polyploidy:** A condition in which an organism has more than two sets of homologous chromosomes. - Common in plants (e.g., wheat, potatoes) and less common in animals (e.g., some fish, amphibians). - **Polyploid Species:** Can arise from a single error in cell division, such as a failure of chromosomes to separate properly, with one set of chromosomes being duplicated in the offspring. ## 8.23 Alterations of Chromosome Structure Can Cause Birth Defects and Cancer - **Chromosome Structure Alterations:** Can occur due to errors in meiosis or damaging agents (e.g., radiation), and can lead to: - **Deletion:** A chromosomal fragment is removed, leading to the loss of genes. - **Duplication:** A chromosomal segment is copied and inserted into the homologous chromosome. - **Inversion:** A chromosome segment is removed and then reinserted opposite to its original orientation. - **Translocation:** A chromosome segment is moved to a nonhomologous chromosome. - **Consequences of Chromosome Structure Alterations:** Some can result in the loss of essential genes, leading to birth defects, while others can contribute to cancer. - For example, translocation in chromosome 22, associated with chronic myelogenous leukemia (CML). ## 8.14 Mitosis and Meiosis Have Important Similarities and Differences - **Mitosis:** Produces two genetically identical diploid cells; used for Growth, tissue repair, asexual reproduction. - **Meiosis:** Produces four genetically unique haploid cells; used for Sexual reproduction. ## 8.15 Independent Orientation of Chromosomes in Meiosis and Random Fertilization Lead to Varied Offspring - **Independent Assortment:** Chromosomes pairs are randomly distributed at metaphase I of meiosis resulting in many different chromosome combinations in gametes. - **Random Fertilization:** the fusion of sperm and egg cells is random. ## 8.16 Homologous Chromosomes May Carry Different Versions of Genes - **Genes:** Encode for the same characteristic but have different versions, called alleles. - **Crossing Over:** The exchange of corresponding segments between non-sister chromatids during prophase I of meiosis. - Creates recombinant chromosomes, which have new gene combinations. ## 8.17 Crossing Over Further Increases Genetic Variability - **Recombinant Chromosomes:** Result from crossing over. They contain combinations of genes different than those of the parent chromosomes. ## 8.18 Accidents During Meiosis Can Alter Chromosome Number - **Nondisjunction (failure to separate during meiosis):** - Can cause a diploid gamete, instead of a haploid. - Leads to an individual with an abnormal number of chromosomes—which can cause a syndrome or possibly be fatal. ## 8.19 A Karyotype Is a Photographic Inventory of An Individual's Chromosomes - **Karyotype:** An ordered display of chromosomes arranged in pairs. - **Creating a Karyotype:** 1. Obtain a blood sample. 2. Treat lymphocytes with a chemical to stimulate cell division. 3. Treat lymphocytes with a chemical to arrest cell division at metaphase. 4. Capture images of chromosomes. 5. Arrange chromosomes in a set of pairs. - **Sex Chromosomes:** Those that determine an individual's sex. - Humans: X and Y chromosomes. - **Autosome:** Any other chromosome other than a sex chromosome. ## 8.20 An Extra Copy of Chromosome 21 Causes Down Syndrome - **Trisomy 21:** A condition where there are three copies of chromosome 21 in each cell—causing **Down Syndrome.** - **Down Syndrome:** A syndrome characterized by: - **Physical Characteristics:** Short stature, a flattened nose bridge, a skin fold at the inner corner of the eye, and small, irregular teeth. - **Health Issues:** Heart defects, susceptibility to respiratory infections, and intellectual delays. - **Incidence of Down Syndrome:** - Affects about one in 850 children. - The risk increases with the mother's age. ## 8.21 Abnormal Numbers of Sex Chromosomes Do Not Usually Affect Survival - **Sex Chromosome Number Disruption:** Often causes milder health issues compared to an abnormal number of autosomes. - **Klinefelter Syndrome (XXY):** Men with an extra X chromosome. - Often have abnormally small testes, are usually sterile, may have subnormal intelligence, and may have female body characteristics. - **Turner Syndrome (XO):** Women only have one X chromosome. - Often have short stature, a web of skin extending between the neck and shoulders, and sterile sex organs. - **XYY Syndrome:** Males with an extra Y chromosome. - Typically have normal intelligence, are fertile, and are typically taller than average. - **XXX Syndrome:** Females with an extra X chromosome. - Often have normal intelligence, are fertile, and are typically taller than average. ## 8.22 New Species Can Arise From Errors In Cell Division - **Polyploidy:** Condition where an organism has more than two sets of homologous chromosomes. - **Polyploid Species:** Can arise from a single error in cell division, such as a failure of chromosomes to separate properly, with one set of chromosomes being duplicated. - Common in plants; less common in animals. ## 8.23 Alterations of Chromosome Structure Can Cause Birth Defects and Cancer - **Chromosome Structure Alterations:** Occur due to errors in meiosis or damaging agents (e.g., radiation). - **Deletions:** A fragment of a chromosome is lost, resulting in the loss of genes. - **Duplications:** A segment of a chromosome is copied and inserted into the homologous chromosome. - **Inversions:** A chromosome segment is removed and then reinserted opposite to its original orientation. - **Translocations:** A chromosome segment is moved to a different nonhomologous chromosome. - **Consequences of Chromosome Structure Alterations:** - Some can result in the loss of essential genes, leading to birth defects. - Others can contribute to cancer; for example, translocation in chromosome 22, which is associated with chronic myelogenous leukemia (CML). ## 8.24 How Does the Rate of Cell Division Affect the Lives of Organisms - **Regulating Cell Division:** Important for growth and development of organisms. - **Anchorage Dependence:** Cells must be in contact with a solid surface to divide. - **Density-Dependent Inhibition:** Cells stop dividing when they touch each other. - **Growth Factors:** Act as signals to regulate cell division. ## 8.25 How Do Cells Divide and What Regulates the Processes - **Cell Cycle Control System:** A set of molecules within the cell that trigger and coordinates key events in the cell cycle, such as mitosis. - **Checkpoints:** Critical control points— G1, G2, and M — where the cell cycle control system directs the cell to either proceed or stop until the proper signals are received. - **Go Phase:** A non-dividing state. - **Growth Factors:** Are necessary for growth and reproduction in most animal cells. - **Signal Transduction Pathways:** How growth factors initiate a series of reactions leading to the activation of the cell cycle control system. ## 8.26 How Can We Learn More About The Underlying Biology of Cancer - **Cancer:** Cells fail to heed the normal signals that regulate the cell cycle. - **Cancer Cells:** - Divide excessively. - Often synthesize their own growth factors. - May be immortal. - Can invade other tissues and spread (metastasis). - **Tumors:** Masses of cancer cells. - **Benign Tumors:** Do not spread. - **Malignant Tumors (Cancers):** Can invade other body tissues. - **Treatmetn for Cancer:** - **Surgery:** Removing the tumor. - **Radiation Therapy:** Damages cancer cells by disrupting their DNA. - **Chemotherapy:** Uses drugs to disrupt cell cycle and kill cells. ## 8.27 What are the Key Differences Between Mitosis and Meiosis - **Mitosis:** Produces two identical diploid cells, used for growth, tissue repair, and asexual reproduction. - **Meiosis:** Produces four genetically unique haploid cells used for sexual reproduction. ## 8.28 How Does Meiosis Contribute to Genetic Diverisity - **Independent Assortment:** Chromosomes pair up randomly during meiosis I. - **Crossing Over:** Exchange of genetic material between chromosomes during prophase I. - **Random Fertilization:** The union of gametes is random. ## 8.29 What is the Relationship Between Genome Alterations and Cancer - **Genome Alterations (Changes in Chromosome Number and Structure):** Result from errors in meiosis or from damaging agents, such as radiation. - **Deletion:** Loss of chromosome segments. - **Duplication:** Copying of chromosome segments. - **Inversion:** Reversal of chromosome segments. - **Translocations:** Movement of chromosome segments. - **Nondisjunction:** Failure of chromosomes to separate properly. - **Genome Alterations:** Can result in: - **Birth Defects:** Loss of essential genes. - **Cancer:** Changes to genes regulating cell division, leading to uncontrolled growth (e.g. chronic myelogenous leukemia). ## 8.30 How Does Polyploidy Affect Organisms - **Polyploidy:** Condition where an organism has more than two sets of homologous chromosomes. - Often arises from nondisjunction events. - **Polyploid Organisms:** Can be new, distinct species, or have altered traits from their diploid ancestors. - More common in plants. - Can cause problems during sexual reproduction. ## 8.31 How Do We Study Chromosomes - **Karyotype:** A photographic inventory of the chromosomes of a cell. - **Creating a Karyotype:** 1. Collect (usually blood) cells. 2. Culture cells to promote cell division. 3. Stop mitosis at metaphase when chromosomes are most condensed. 4. Stain and photograph chromosomes, and arrange them in order of size. - **Karyotype Analysis:** - Identifies abnormal chromosome number. - Reveals structural changes in chromosomes. ## 8.32 How Does the Cell Cycle Control System Work - **Cell Cycle Control System:** A set of molecules that monitor and manage specific events in the cell cycle. - **Checkpoints:** G1, G2 and M: Specific points where the cell cycle can be stopped or allowed to proceed. - **Growth Factors:** Proteins that stimulate cell division. - **Signal Transduction Pathways:** How growth factors trigger a sequence of events leading to the activation of the cell cycle control system. ## 8.33 How Does Cancer Affect Our Health - **Cancer:** A disease of the cell cycle—where cells fail to heed the normal signals that regulate the cell cycle. - **Cancer Cells:** Divide uncontrollably, invade other tissues, and often metastasize. - **Causes:** - Genome Alterations: Changes in chromosome number, changes in gene expression, mutations in genes. - Environmental Factors: Exposure to carcinogens. - **Treatment:** - **Surgery:** To remove tumors. - **Radiation Therapy:** Destroys cancer cells with radiation. - **Chemotherapy:** Uses drugs to kill cancer cells. ## Connecting the Concepts | | Mitosis | Meiosis | | ------------------------ | ---------------------------------------- | ------------------------------------- | | Number of chromosomal duplications | One | One | | Number of cell divisions | One | Two | | Number of daughter cells produced | Two | Four | | Number of chromosomes in daughter cells | Same number as parent | Half the number as the parent | | How the chromosomes line up during metaphase | Single file | Pairs | | Genetic relationship of daughter cells to parent cell | Genetically identical | Genetically unique | | Functions performed in human body | Growth, repair, asexual reproduction | Production of gametes |