Genetics PDF: Introduction, DNA, and Cell Structure

GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL pea-pod size, pea-pod color, and flower OUTLINE...

GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL pea-pod size, pea-pod color, and flower OUTLINE position). I. Genetics o​ He repeated this over two generations of plants and found that he could obtain A.​ Historical Context consistent ratios of traits. II. Cell o​ In turn, he deduced four important A.​ Structure and Basic Functions principles of inheritance: III. Difference Between DNA, Chromosomes, and 1.​ Hereditary determinants are Genes called genes. A.​ Chromosomes 2.​ Genes exist in pairs, called B.​ DNA alleles (variations) which may C.​ Genes be dominant or recessive. 3.​ Genes are segregated in the GENETICS gametes which are ​ Genetics is the study of heredity in general and of consequently carriers of only genes in particular. Genetics forms one of the one gene pair. central pillars of biology and overlaps with many 4.​ Fertilization, in which two other areas, such as agriculture, medicine, and gametes fuse, is random. (Even biotechnology (genetic engineering). if you control the parent, you can’t control the offspring) HISTORICAL CONTEXT ​ Greek philosophers explored the idea of human inheritance some 1600 years after 5000 BC. The notable Aristotle suggested that traits acquired throughout an organism’s lifetime could be transmitted to their offspring. o​ Aristotle supplemented this hypothesis with the theory of pangenesis which described how these traits could be passed on; particles called gemmules (sex cells) (each organ of the body sends it copy in the gametes; encapsulated these traits and allowed them to be transmitted to reproductive cells). ​ Swiss physician Friedrich Miescher discovered a ​ Aristotle’s theory was rejected by August substance he called nuclein in 1869. Weismann, a german evolutionary biologist, by o​ Later, he isolated a comparatively purer proposing the Germ Plasm Theory (1883) — germ sample of this same material from the plasm, which is independent from all other cells of sperm of salmon. the body (somatoplasm/somatic cells), is the o​ In 1889, his pupil, Richard Altmann, essential element of germ cells (eggs and renamed nuclein to nucleic acid. This sperm/sex cells/gametes) and is the hereditary substance was found to exist only in the material that is passed from generation to chromosomes. generation. o​ This discovery built on earlier work by ​ Gregor Mendel: The Father of Genetics Walter Flemming who described the o​ A monk who performed a meticulous appearance and behavior of series of experiments with pea plants in chromosomes in 1882. 1857. ​ In 1902, Theodor Boveri and Walter Sutton o​ Selected specific characteristics of pea independently postulated that chromosomes were plants to study (plant height, seed not only the carriers of hereditary units but were texture, seed color, flower color, organized so that different locations (gene loci) of the chromosomes corresponded to specific ​ ​ RPSY - 2026​ 1 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL hereditary traits. (Chromosomes not only carry but o​ From the x-ray diffraction images encodes different traits) Franklin obtained, she demonstrated o​ Boveri did this by examining that DNA contained a regularly chromosomal behavior during cell repeating helical structure. The division and gamete formation. images allowed precise calculations of o​ This formed the basis of cytogenetics the molecular spacing in DNA. which describes the structure, function, ​ Building on Franklin’s work two scientists, James and inheritance of chromosomes. Watson and Francis Crick, made a model of the ​ In 1929, Phoebus Levene at the Rockefeller DNA structure approximately 2 years later. Institute identified the components that make up a o​ Their model was that of a double helix DNA molecule. Those components are: that consisted of evenly spaced pairs of o​ The Four Bases (Adenine, Cytosine, bases connecting the two strands. It Guanine, Thymine) was possible to predict the o​ Sugar (Deoxyribose, Ribose) measurements between bases and the o​ Phosphate number of bases per turn; further, there ▪​ He showed that the components were strict base-pairing rules. of DNA were linked in the order o​ To account for their measurements, they phosphate-sugar-base. discovered that Thymine could only pair Crucially, he distinguished the with Adenine and Guanine with two ribose Cytosine. This concurred with Chargaff’s subtypes–deoxyribose and rule. ribose. Levene coined the o​ Chargaff’s rules state that DNA from any arrangement of the sugar, base, cell of all organisms should have a 1:1 and phosphate group a ratio (base pair rule) of pyrimidine and nucleotide. purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. A DECADE LATER Notable Discoveries Beyond the Double Helix ​ Robert W. Holley, Har Gobind Khorana and Marshall W. Nirenberg won a Nobel Prize for their work deciphering how DNA is related to protein synthesis. o​ They established the central dogma of information transfer from DNA to RNA to protein. ​ In 1949, Andre Boivin and his students Colette and ​ In 1977, Frederick Sanger, Allan Maxam, and Roger Vendrely found that the nuclei of germ cells Walter Gilbert developed methods to sequence contained only half the amount of DNA than that DNA. of somatic cells. o​ This was supplemented in 1983 by Kary ​ In the 1940s, Erwin Chargaff found that the base Mullis, who invented the polymerase composition (ACTG) differed between species and chain reaction (PCR) to amplify DNA. that ratios between them were invariable; the o​ Together these methods paved the way quantity of adenine was equal to that of thymine. for sequencing of the human genome The same ratio of 1:1 was seen for cytosine and which began in 1990 and was guanine. This discovery later became known as completed 13 years later, in full. Chargaff’s Rule. ​ In 1952, British researcher Rosalind Franklin crystallized a molecule of DNA. ​ ​ RPSY - 2026​ 2 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL TODAY ​ The focus on DNA has exploded to include ways of “editing” the genome, using novel methods to change the information it encodes in highly specific ways. ​ Further, lesser known areas of the genome are under study; the field of epigenomics is rapidly expanding, allowing us to understand how and why genome behavior differs substantially between individuals. ​ Genetic engineering. 1.​ Cell Membrane – (cell/plasma membrane) the cell membrane surrounds the cell and is a CELL selective barrier between the interior and exterior. ​ Fundamental unit of life. o​ Its primary role lies in regulating the ​ The cell is the basic structure of the body. The passage of substances, including human body is built of billions and trillions of cells. nutrients and waste materials. Cells of various organs vary according to their o​ Within it, specialized proteins play a function. crucial role in facilitating molecular ​ Each cell contains the hereditary material and can transport and cellular communication. make copies of itself by reproducing and ▪​ Phospholipid bilayer; hydrophilic multiplying. After a specific life span, the old cells head (polar), hydrophobic tail die off. (nonpolar) ▪​ Semi-permeable TYPES OF CELLS 2.​ Cell nucleus – an organelle that houses DNA, located in the center of eukaryotic cells. PROKARYOTIC EUKARYOTIC o​ Its primary function is to store and Lack a defined nucleus Have a defined nucleus safeguard genetic information, controlling gene expression and DNA Prokaryotic – dispersed Plant – cellulose cell wall; replication. genetic material in the chloroplasts and cytoplasm. vacuoles. o​ It also contains the nucleolus, which is involved in ribosome synthesis. Animal – rigid cell wall; ▪​ Command center; largest may have flagella. ▪​ Nuclear membrane ▪​ Nucleolus produces ribosomes Protist – they can have a → protein synthesis cell wall, without ▪​ Nucleoplasm – gel-like fluid differentiated tissues. structure ▪​ Nuclear pores – instructions Fungal – chitin cell wall; from DNA pass through the they are heterotrophs. pores 3.​ Cytoplasm – the cytoplasm is a gel-like matrix STRUCTURE AND BASIC FUNCTIONS containing water, salts, proteins, and other ​ These components work together to maintain molecules. It occupies the intracellular space cellular homeostasis and perform essential life between the cell membrane and the nucleus. activities. o​ It plays a crucial role in biochemical ​ Composed of several fundamental components: reactions, energy production, and substance transport. Essential for cellular metabolism, it provides structural support to the cell. ▪​ Fluid like nucleoplasm ​ ​ RPSY - 2026​ 3 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL PROTEIN SYNTHESIS 7.​ Mitochondria – present in eukaryotic animal ​ Building and repairing cellular structures, and plant cells. Their primary function is energy regulating biological processes, and expressing generation through cellular respiration (ATP specific characteristics of each organism. production). o​ The double membrane of mitochondria 4.​ Ribosome – essential organelles for cellular allows for the organization of various functioning and survival. stages of the respiratory chain, making it o​ They synthesize proteins using the crucial for cellular function and survival. genetic information from messenger ▪​ Glucose → ATP/energy RNA (mRNA), which is crucial for 8.​ Chloroplasts – exclusive to plant cells and cellular structure, function, and photosynthetic organisms, chloroplasts carry regulation. out photosynthesis, converting solar energy o​ Ribosomes are located in the into chemical energy. cytoplasm and the rough o​ During photosynthesis, they synthesize endoplasmic reticulum. glucose and other organic compounds 5.​ Endoplasmic Reticulum – a network of using carbon dioxide and water, interconnected membranes that extends from releasing oxygen as a byproduct. the nuclear membrane to the cell membrane. It o​ They are responsible for the crucial plays a fundamental role in the transport, production of oxygen that sustains the processing, and distribution of proteins and planet. lipids within the cell. There are two main types of ER: CELLULAR DIGESTION o​ The Rough Endoplasmic Reticulum ​ It involves breaking down molecules and unwanted (RER) is studded with ribosomes and materials, enabling the recycling of nutrients and is involved in the synthesis and cellular maintenance. modification of proteins. ▪​ Site for protein synthesis. 9.​ Lysosomes – they contain digestive enzymes o​ The Smooth Endoplasmic Reticulum (kaon sa basura) that break down molecules (SER) specialized in lipid synthesis, and unwanted cellular materials. carbohydrate metabolism, and o​ They facilitate cellular digestion, by detoxification. disposing of waste, recycling nutrients, 6.​ Golgi Apparatus – key in the processing and and defending against pathogenic packaging of proteins and lipids produced in the invasions. ER. ▪​ Suicide bag of the cell o​ It synthesizes carbohydrates and ▪​ Apoptosis – cell death if beyond lipoproteins and is essential for repair maintaining the cell’s internal balance 10.​ Peroxisomes – they contain enzymes that and facilitating communication with the degrade hydrogen peroxide and toxic outside. compounds, thereby protecting the cell from o​ Composed of a series of flattened sacs oxidative damage. called cisternae, it acts as the shipping o​ Additionally, they play a role in the center of the cell, sorting and packaging synthesis and degradation of lipids proteins into vesicles for transport and and bile acids, regulating lipid distribution. metabolism and overall homeostasis. ▪​ Collect → Package → Distribute ▪​ Vesicles → rider/delivers where SUPPORT AND MOVEMENT it is needed; looks like a basket ​ Maintaining cellular shape, enabling cellular movement and division, are essential for its ENERGY SUPPLY functioning and survival. ​ To carry out vital functions and necessary metabolic processes essential for the proper functioning of the cell and/or organism. ​ ​ RPSY - 2026​ 4 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL 11.​ Cytoskeleton – it is composed of protein DIFFERENCE BETWEEN DNA, CHROMOSOMES, filaments (microtubules, microfilaments, and AND GENES intermediate filaments) and provides support CHROMOSOMES and enables movement in eukaryotic cells. ​ Within the nucleus, the DNA strands are tightly o​ Its specific functions encompasses packed to form chromosomes. During the cell stability, intracellular transport, and division, the chromosomes are visible. contraction. Furthermore, it regulates ​ Each chromosome has a constriction point called cellular shape and plays a role in the centromere from where two arms are formed. division, migration, and communication. The short arm of the chromosome is labeled the “p ▪​ Maintain shape and structure arm.” The long arm of the chromosome is labeled ▪​ Made of structural proteins the “q arm.” 12.​ Flagella and Cilia – specialized structures for ​ Humans typically have 23 pairs of chromosomes, movement. They are elongated and enable for a total of 46. Twenty-two of these pairs, called locomotion in liquid environments, whereas cilia autosomes, look the same in both males and are shorter and create coordinated flow on females. the cell surface. ​ The 23rd pair is called the sex chromosomes and o​ Composed of microtubules in a ‘9+2’ differs between males and females. Females have pattern, they are essential for sperm two copies of the X chromosome or XX, while males motility. have one X and one Y chromosome. STORAGE AND TRANSPORTATION ​ They manage nutrients, eliminate waste, and regulate metabolic processes. 13.​ Vacuoles – membrane-bound organelles found in plant cells and some animal cells. They store nutrients, water, ions, and waste materials, regulating turgor pressure and osmotic balance. o​ Vacuoles can also be involved in the digestion of substances and serve as a defense mechanism against predators by containing toxins. ▪​ Stores water ▪​ Central vacuole biggest sa ​ 23 Chromosomes and their functions: with plants advancing research techniques, it has become 14.​ Vesicles and Endosomes – membranous possible to locate and analyse the functions of all vesicles that transport specific materials the 23 chromosomes in humans. between organelles and the cell membrane. o​ Vesicles – they transport materials from the endoplasmic reticulum and the Golgi apparatus to other destinations. o​ Endosomes – they capture and distribute materials for degradation, recycling, or their incorporation into metabolic pathways. ​ ​ RPSY - 2026​ 5 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL ​ DNA Base Pairs o​ DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. o​ The Adenine – Thymine base pair is held together by 2 hydrogen bonds DNA while the Guanine – Cytosine base pair ​ Responsible for building and maintaining your is held together by 3 hydrogen bonds. human structure. o​ Adenine – Uracil → 2 hydrogen bonds (RNA). The Properties of DNA o​ The chemical structures of Thymine and ​ Where is DNA found? → DNA, or Cytosine are smaller, while those of deoxyribonucleic acid, is the hereditary material that Adenine and Guanine are larger. lies within the nucleus of all cells in humans and o​ Size and structure of the specific other living organisms. nucleotides cause Adenine and ​ What is the DNA made of? → DNA contains four Thymine to always pair together while chemical bases/nitrogenous bases: Cytosine and Guanine always pair o​ Adenine (A) – purine (double ring) together. o​ Guanine (G) – purine o​ DNA in humans contains around 3 o​ Cytosine (C) – pyrimidine (single ring) billion bases. These bases are o​ Thymine (T) – pyrimidine sequenced differently for various ▪​ Including Uracil of RNA information that needs to be transmitted. GENES ​ Genes are hereditary material that lies within the cell nucleus. Genes, which are made up of DNA, act as instructions to make molecules called proteins. ​ The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes. ​ Every person has two copies of each gene, one inherited from each parent. ​ ​ RPSY - 2026​ 6 GENETICS​ BIO 207P LEC | LECTURE | PRELIMS INTRODUCTION TO GENETICS AND CELL FUN FACT ​ The Human Genome Project has determined that humans have an estimated 30,000 genes. ​ What are karyotype and idiogram? o​ A karyotype is the entire set of chromosomes of a cell or individual, as seen during mitotic metaphase. It helps to determine the size, shape, number and type of chromosomes. o​ Idiogram is nothing but the diagrammatic representation of a karyotype. ​ What is cytological mapping? o​ Cytological maps or physical maps determine the physical locations of a gene in a chromosome with the help of genetic markers. o​ Cytological maps are more accurate in terms of genome representation than genetic maps. The genetic map provides insight into the nature of various regions of the chromosome and is comparatively less efficient. ​ ​ RPSY - 2026​ 7 GENETICS​ BIO 207P | LECTURE | PRELIMS CELL CYCLE: MITOSIS AND MEIOSIS o​ Mitosis involves the separation of OUTLINE copied chromosomes into separate I. Terms and Concepts to Understand cells. ​ Unregulated Cell Division Can Lead to Cancer A.​ Core Concepts o​ Cell-cycle checkpoints normally B.​ Basic Definitions ensure that DNA replication and mitosis II. Chromosome Structure occur only when conditions are III. The Cell Cycle favorable and the process is working A.​ Mitosis correctly. o​ Mutations in genes that encode cell-cycle proteins can lead to unregulated growth, resulting in tumor formation and ultimately invasion of cancerous cells to other organs. BASIC DEFINITIONS ​ In order to better understand the concept of cell division and genetics, some basic definitions are in order: o​ Gene – basic unit of heredity; codes for a specific trait o​ Locus – the specific location of a gene on a chromosome (locus - plural loci) o​ Genome – the total hereditary endowment of DNA of a cell or organism o​ Somatic cell – all body cells except TERMS AND CONCEPTS TO UNDERSTAND reproductive cells ​ Cell division involves the distribution of identical o​ Gamete – reproductive cells (i.e., sperm genetic material, DNA, to two daughter cells. & eggs) ​ What is most remarkable is the fidelity with which o​ Chromosome – elongate cellular the DNA is passed along, without dilution or error, structure composed of DNA and protein from one generation to the next. – they are the vehicles which carry DNA in cells CORE CONCEPTS o​ Diploid (2n) – cellular condition where ​ All Organisms Consist of Cells and Arise from each chromosome type is represented Preexisting Cells by two homologous chromosomes o​ Mitosis is the process by which new o​ Haploid (n) – cellular condition where cells are generated. each chromosome type is represented o​ Meiosis is the process by which by only one chromosome gametes are generated for reproduction. o​ Homologous chromosome – ​ The Cell Cycle Represents All Phases in the Life chromosome of the same size and of a Cell shape which carry the same type of o​ DNA replication (S phase) must genes precede mitosis, so that all daughter o​ Chromatid – one of two duplicated cells receive the same complement of chromosomes connected at the chromosomes as the parent cell. centromere o​ The gap phases separate mitosis from o​ Centromere – region of chromosome S phase. This is the time when where microtubules attach during molecular signals mediate the switch in mitosis and meiosis cellular activity. ​ ​ RPSY - 2026​ 1 GENETICS​ BIO 207P | LECTURE | PRELIMS CELL CYCLE: MITOSIS AND MEIOSIS CHROMOSOME STRUCTURE THE CELL CYCLE ​ Composed of DNA and protein (histones) all tightly wrapped up in one package. ​ Duplicated chromosomes are connected by a centromere. ​ Actively dividing eukaryote cells pass through a series of stages known collectively as the cell cycle. ​ Two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides. o​ G1 phase. Metabolic changes prepare the cell for division. At a certain point—the restriction point—the cell is committed to division and moves into the S phase. o​ S phase. DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids. o​ G2 phase. Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. o​ M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis). o​ The period between mitotic divisions – that is, G1, S, and G2 – is known as ​ Chromosomes 1 & 2 are homologous interphase. chromosomes. ​ Chromosomes 3 & 4 are homologous MITOSIS chromosomes. ​ Mitosis is a form of eukaryotic cell division that ​ Chromosomes 1 & 3 came from the mother. produces two daughter cells with the same ​ Chromosomes 2 & 4 came from the father. genetic component as the parent cell. ​ Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. ​ In actively dividing animal cells, the whole process takes about one hour. ​ ​ RPSY - 2026​ 2 GENETICS​ BIO 207P | LECTURE | PRELIMS CELL CYCLE: MITOSIS AND MEIOSIS METAPHASE ​ The chromosomes align themselves along the metaphase plate of the spindle apparatus. ANAPHASE ​ The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each chromosome are pulled apart – or “disjoin” – and move to the opposite ends of the cell, pulled by spindle fibers attached to the kinetochore regions. ​ The separated sister chromatids are now referred to as daughter chromosomes. ​ It is the alignment and separation in metaphase and anaphase that is important in ensuring that each daughter cell receives a copy of every chromosome. TELOPHASE PROPHASE ​ The final stage of mitosis, and a reversal of many ​ Prophase occupies over half of mitosis. The of the processes observed during prophase. nuclear membrane breaks down to form a ​ The nuclear membrane reforms around the number of small vesicles and the nucleolus chromosomes grouped at either pole of the cell, the disintegrates. chromosomes uncoil and become diffuse, and the ​ A structure known as the centrosome (centrioles) spindle fibers disappear. duplicates itself to form two daughter centrosomes (centrioles) that migrate to opposite ends of the cell. CYTOKINESIS ​ The centrosomes organize the production of ​ The final cellular division to form two new cells. microtubules that form the spindle fibres that ​ In plants a cell plate forms along the line of the constitute the mitotic spindle. metaphase plate; in animals there is a constriction ​ The chromosomes condense into compact of the cytoplasm. structures. Each replicated chromosome can now ​ The cell then enters interphase – the interval be seen to consist of two identical chromatids (or between mitotic divisions. sister chromatids) held together by a structure known as the centromere. PROMETAPHASE ​ The chromosomes, led by their centrosomes (centrioles), migrate to the equatorial plane in the midline of the cell–at right-angles to the axis formed by the centrosomes. ​ This region of the mitotic spindle is known as the metaphase plate. ​ The spindle fibers bind to a structure associated with the centromere of each chromosome called a kinetochore. ​ Individual spindle fibers bind to a kinetochore structure on each side of the centromere. The chromosomes continue to condense. ​ ​ RPSY - 2026​ 3 GENETICS​ BIO 207P | LECTURE | PRELIMS ADDITIONAL INFORMATION FOR PRELIMS 1. How does mitosis contribute to both genetic 5. Compare and contrast the role of mitosis in stability and genetic variation in organisms? unicellular and multicellular organisms. Answer: Mitosis ensures genetic stability by producing Answer: In unicellular organisms (e.g., bacteria, daughter cells that are genetically identical to the parent protists), mitosis is a form of asexual reproduction, cell, maintaining the same DNA sequence. However, allowing the organism to increase in population. In occasional errors such as mutations during DNA multicellular organisms, mitosis is used primarily for replication in interphase can introduce genetic variation. growth, development, repair, and maintenance of If these mutations occur in somatic cells, they may affect tissues, rather than reproduction. While both rely on cell function but are not inherited. mitosis for cell division, the purpose differs significantly between the two groups. 2. What would be the consequences if spindle fibers failed to attach to one or more chromosomes during 6. What would happen if a mutation disrupted the metaphase? regulation of the G2/M checkpoint in the cell cycle? Answer: If spindle fibers fail to attach to some Answer: If the G2/M checkpoint is disrupted, cells may chromosomes, those chromosomes may not align enter mitosis with damaged or unreplicated DNA, properly at the metaphase plate and could be unequally leading to genomic instability. This increases the risk distributed during anaphase. This could result in of mutations accumulating, which can contribute to aneuploidy, where one daughter cell receives extra diseases such as cancer, where abnormal cells chromosomes while another is missing some, potentially continue dividing uncontrollably. leading to diseases like cancer or Down syndrome (if occurring in meiosis instead). 7. How does mitotic failure lead to polyploidy in some cells, and what are the consequences of 3. How does mitosis ensure the maintenance of polyploidy? chromosome number across cell generations? What mechanisms are in place to prevent errors? Answer: If a cell fails to complete cytokinesis after mitosis, it may retain multiple sets of chromosomes, Answer: Mitosis maintains chromosome number by leading to polyploidy (more than two sets of duplicating DNA during interphase (S phase) and chromosomes). In plants, polyploidy can be beneficial equally distributing the sister chromatids during (e.g., larger fruit, increased stress tolerance), but in anaphase. Checkpoints in the cell cycle (G1, G2, and animals, it often results in lethal developmental M phase checkpoints) help detect DNA damage, defects. incomplete replication, or improper spindle attachment, preventing faulty cell division and ensuring accurate 8. Why is apoptosis (programmed cell death) chromosome segregation. necessary in tissues where mitosis is highly active? 4. Why do cancer cells often exhibit uncontrolled Answer: Apoptosis helps remove damaged, old, or mitosis, and how does this impact the body? excessive cells produced by mitosis, preventing tumor formation and ensuring tissue homeostasis. Without Answer: Cancer cells bypass normal cell cycle apoptosis, unchecked cell growth can lead to cancer or regulation due to mutations in genes controlling cell hyperplasia (excess tissue growth), disrupting normal division, such as proto-oncogenes (which become function. oncogenes) or tumor suppressor genes (e.g., p53). This leads to uncontrolled mitosis, excessive cell growth, 9. If mitosis produces identical daughter cells, how and the formation of tumors, which can disrupt normal do specialized cells (e.g., neurons, muscle cells) tissue function, consume vital nutrients, and metastasize arise from mitotic divisions? to other parts of the body. Answer: Specialized cells arise through differentiation, which is controlled by gene expression rather than changes in DNA sequence. Even though mitotic ​ ​ RPSY - 2026​ 1 GENETICS​ BIO 207P | LECTURE | PRELIMS ADDITIONAL INFORMATION FOR PRELIMS daughter cells have identical DNA, external signals (hormones, growth factors) and internal regulators determine which genes are active, leading to different cell functions. 10. Why do some cells, such as nerve cells and cardiac muscle cells, enter G0 phase and rarely undergo mitosis? Answer: Cells in G0 phase are in a quiescent (non-dividing) state because they have completed their function and do not need constant renewal. Neurons and cardiac muscle cells are highly specialized and need to maintain long-term stability and function. If these cells were to divide uncontrollably, it could disrupt the nervous or circulatory system. However, limited regeneration can occur in certain cases. ​ ​ RPSY - 2026​ 2