General Biology 1 Past Paper PDF 2024/2025 (BOWEN UNIVERSITY)

BOWEN UNIVERSITY IWO, OSUN STATE, NIGERIA. COLLEGE: AGRICULTURE, ENGINEERING AND SCIENCE PROGRAMME: PURE AND APPLIED BIOLOGY SESSION: 2024/2025 SEMESTER: FIRST COURSE CODE: BIO 101 CREDIT UNIT: 2 COURSE TITLE: GE...

BOWEN UNIVERSITY IWO, OSUN STATE, NIGERIA. COLLEGE: AGRICULTURE, ENGINEERING AND SCIENCE PROGRAMME: PURE AND APPLIED BIOLOGY SESSION: 2024/2025 SEMESTER: FIRST COURSE CODE: BIO 101 CREDIT UNIT: 2 COURSE TITLE: GENERAL BIOLOGY 1 LECTURE DAYS: THURSDAY TIME: 8 am – 10 am 18th – 25th November 2024 – Two weeks Lecturer: Jacob O. Popoola Lecture Note/Guide Introduction Biology is the study of life. You have been introduced to the cellular basis of life, characteristics, and classification of organisms, general reproduction, and interrelationships of organisms amongst others. In this lecture module, you will be introduced to the basic knowledge of chromosomes, genes, and DNA as genetic materials. You will also be exposed to the basics of heredity and evolution. There are two modules in this section. Module I: Chromosomes, genes; their relationships and importance (One Week – 18th – 22nd November) Module II: Heredity and Evolution (25th – 29th November 2024) These modules will introduce you to a wide range of topics including: 1. Chromosomes, genes; their relationships, and importance 2. Heredity and evolution: Introduction to Darwinism and Lamarckism, Mendelian laws 3. Explanation of key genetic terms Module 1: Chromosomes, genes; their relationships, and importance What are Genes, DNA, and Chromosomes? Genetics is a complex field of study involving the study of inheritance or heredity in nature. Simply, it is the study of heredity which is the way and manner genetic ‘characteristics’ or ‘traits’ are inherited from parents to the offspring from generation to generation. These traits are controlled by coded information found in every cell of living organisms. Genetic code is written in DNA (Deoxyribonucleic acid), genes, and chromosomes. Together, these units make up the complete set of genetic instructions for every individual—referred to as a genome—including our sex, appearance, and medical conditions we may be at risk of. No two people have the same genome. And no two individuals are exactly alike! This lecture offers a basic explanation of genetics, including what genes, DNA, and chromosomes are, their relationships, and their importance. 1 What is a Genome? A genome is the complete set of genetic instructions that determine the traits (characteristics and conditions) of an organism. It is made up of DNA, genes, and chromosomes. I will break it down as follows: 1. Deoxyribonucleic Acid (DNA) is a molecule in cells that carries the genetic information. It is made up of building blocks. The genetic coding of our traits is based on how these building blocks are arranged. 2. Genes are segments/fragments of DNA that determine our traits. Every human has between 20,000 and 25,000 different genes, half of which are inherited from our biological mothers and the other half from our biological fathers. 3. Chromosomes are long, bundled strands of DNA, each of which contains many genes. In humans, there are two sets of 23 chromosomes in a cell. Each set is inherited from our biological parents making a total of 46. Your genome determines how your body will develop before birth. It directs how you will grow, look, and age. And it will determine how cells, tissues, and organs of the body work (including times when they may not work as they should). While the genome of each species is distinct, every organism within that species has its unique genome. This is why no two people are exactly alike, even twins. What Is a Chromosome? Genes are packaged into bundles known as chromosomes. Humans have 23 pairs of chromosomes for a total of 46 individual chromosomes. Chromosomes are contained within the control center (nucleus) of nearly every cell of the body. One pair of chromosomes called the sex chromosomes, determines whether you are born male or female. Females have a pair of XX chromosomes, while males have a pair of XY chromosomes. The other 22 pairs, called autosomal chromosomes, determine the rest of your body’s makeup. Certain genes within these chromosomes may either be dominant or recessive. Autosomal dominant means that you need only one copy of an allele from one parent for a trait to develop (such as brown eyes or Huntington's disease). Autosomal recessive means that you need two copies of the allele—one from each parent—for a trait to develop (such as blue eyes or cystic fibrosis). Important information on chromosome It is the nuclear unit of genetic information. It continuously divides and is distributed during cell division. The complex of DNA and proteins that make up a chromosome is called chromatin. Two copies of each type of chromosome in nuclei is diploid - 2n, one copy - haploid - n For example, humans have 23 pairs of chromosomes for a diploid number of 46 chromosomes, i.e., 2n = 46, n = 23 - haploid. During replication, each chromosome is duplicated into two exact copies called sister chromatids joined together by a centromere (Figure 1). Chromosomes based on centromere position are shown in Figure 2. Note: DNA, genes, and chromosomes work together to make what organisms are. 2  Figure 1: Chromosome structure Figure 2: Chromosomes on the basis of centromere position. A chromosome has 8 parts: Centromere or primary constriction or kinetochore, chromatids, chromatin, secondary constriction, telomere, chromomere, chromonema, and matrix. Centromere or Kinetochore: It is the primary constriction at the center to which the chromatids or spindle fibers are attached. Its function is to enable movement of the chromosome during the anaphase stage of cell division. Chromatid: During cell division, a chromosome is divided into 2 identical half strands joined by a centromere. A chromatid is each half of the chromosome joined. Each chromatid contains DNA and separates at Anaphase to form a separate chromosome. Both chromatids are attached to each other by the centromere. Chromatin: It is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. Nuclear DNA is highly condensed and wrapped around nuclear proteins in order to fit inside the nucleus. In other words, it is not present as free linear strands. The chromatin consists of DNA, RNA, and protein. 3  Secondary Constriction: It is generally present for the nucleolar organization. Telomere: Telomere is the terminal region of each side of the chromosome. Chromonema: It is a threadlike coiled filamentous structure along which chromomeres are arranged. Chromonema controls the size of the chromosome, and it acts as a site of gene bearing. Chromomeres: These are the bead-like structures present on threads or chromonema. These are arranged in a row along the length of chromonema. The number of chromosomes is constant, and it is responsible for carrying the genes during cell division to the next generation. Matrix: Pellicle is the membrane surrounding each of the chromosomes. Matrix is the jelly-like substance present inside pellicle. It is formed of non-genetic materials. 4  Deoxyribonucleic Acid (DNA) Deoxyribonucleic acid (DNA) is the genetic material or the cell’s hereditary information, found in the chromosomes within the nucleus of eukaryotic cells (cells with a nucleus). DNA is the material that exists in every cell in your body that holds your genetic code. It makes up your body’s instruction manual. It is available in plants, animals, and microorganisms. Within DNA is a unique chemical code that guides your growth, development, and function. Chemical Components of DNA The chemical code is determined by the arrangement of four chemical compounds known as nucleotide bases which include: i. Adenine (A) ii. Cytosine (C) iii. Guanine (G) iv. Thymine (T) The bases pair up with each other—A with T and C with G—to form units known as base pairs. The pairs are then attached to form what ultimately looks like a spiralling ladder, known as a double helix (Figure 3). The specific order, or sequence, of bases, determines which instructions are given for building and maintaining an organism. Human DNA consists of around 3 billion of these bases, 99% of which are the same for all humans. The remaining 1% is what differentiates one human from the next. Nearly every cell in a person’s body has the same DNA. 5 Figure 3: DNA structure - Chromosomes are found carrying DNA in the nucleus of cells. DNA looks like a Ribonucleic Acid (RNA) The ribonucleic acid (RNA) is involved in the protein synthesis. Different types of RNA participate in cellular activities. Messenger RNA (mRNA) carries information from DNA to the ribosomes, where it serves as a template for protein synthesis. Thus, the flow of genetic information in nature is from DNA to RNA and then protein. Two other types of RNA (ribosomal RNA and transfer RNA) are involved in protein synthesis. Other kinds of RNAs are involved in the processing and transport of both RNAs and proteins. The two major processes involved in gene/protein expression/synthesis are transcription and translation. DNA and RNA are polymers of nucleotides, which consist of purine and pyrimidine bases linked to phosphorylated sugars. DNA contains two purines (adenine and guanine) and two pyrimidines (cytosine and thymine). Adenine, guanine, and cytosine are also present in RNA, but RNA contains uracil in place of thymine. The bases are linked to sugars (2′-deoxyribose in DNA, or ribose in RNA) to form nucleosides. Nucleotides additionally contain one or more phosphate groups linked to the 5′ carbon of nucleoside sugars (Figure 4, 6). The chemical structure of DNA/RNA are shown in Figures 3, 4, 5 and 6. 6 Figure 4: Comparison of RNA and DNA Figure 5: The chemical structure of DNA 7 Figure 6: DNA and RNA chemical components What Is a Gene? A gene is a unit of DNA that is encoded for a specific purpose. Some genes provide instructions to produce particular proteins. Proteins are molecules that not only makeup tissues like muscles and skin but also play many critical roles in the structure and function of the body. Genes are small sections of DNA within the genome that code for proteins. They contain the instructions for our individual characteristics – like eye and hair colour. A gene is a segment of DNA that codes for (contains the chemical information necessary for the creation of) a specific enzyme or protein or a polypeptide chain that functions in one or more types of cells in the body. Genes are encoded to produce RNA (ribonucleic acid), a molecule that converts the information stored in DNA to make the protein. How genes are encoded will ultimately determine how you look and how your body works. Every person has two copies of each gene, one inherited from each parent. Different versions of a gene are known as alleles. The alleles you inherit from your parents may determine, for example, if you have brown eyes or blue eyes. Genes only make up between 1% and 5% of the human genome. The rest is made up of noncoded DNA that doesn't produce protein but helps regulate how genes function. A gene is a small section of DNA that contains the instructions for a specific molecule, usually a protein. The purpose of genes is to store information. Each gene contains the information required to build specific proteins needed in an organism. The human genome contains 20,687 protein-coding genes. Genes come in different forms, called alleles. In humans, alleles of particular genes come in pairs, one on each chromosome (we have 23 pairs of chromosomes). If the alleles of a particular gene are the same, the organism is 8  described as homozygous for that gene. If they are different the organism is described as heterozygous for that gene. An individual’s phenotype is determined by the combination of alleles they have. For example, for a gene that determines eye colour there may be several different alleles. One allele may result in blue eyes, while another might result in brown eyes. The final colour of the individual’s eyes will depend on which alleles they have and how they interact. The characteristic associated with a certain allele can sometimes be dominant or recessive. Module II: Heredity and Evolution Introduction The biological science of genetics deals with the mechanism of hereditary and the causes of variation in living organisms. The science of genetics attempts to explain the mechanism and the basis for both similarities and differences between related individuals. Heredity and variations have a significant role in the formation of new species (i.e., speciation) and in organic evolution. Evolution is a process that results in changes in the genetic material of a population over time. Evolution reflects the adaptations of organisms to their changing environments and can result in altered genes, novel traits, and new species. Key Points Heredity and evolution are two fundamental concepts in biology Heredity:- Refers to the passing of traits from parents to offspring through the transmission of genetic information Genetic information is encoded in DNA and is the basis for the development and growth of an organism Heredity determines the traits of an individual Heredity provides the raw material for evolution Evolution shapes the distribution of genetic variation in populations Heredity and evolution are intertwined, with heredity influencing evolution and evolution influencing heredity Relationship: Heredity provides the genetic variation that evolution acts upon Evolution, in turn, shapes the distribution of genetic variation in populations This interplay between heredity and evolution drives the evolution of species 9 Introduction to Darwinism and Larmakism What is evolution? The basic idea of biological evolution is that populations and species of organisms change over time. Today, when we think of evolution, we are likely to link this idea with one specific person: the British naturalist Charles Darwin. In the 1850s, Darwin wrote an influential and controversial book called On the Origin of Species. In it, he proposed that species evolve (or, as he put it, undergo "descent with modification"), and that all living things can trace their descent to a common ancestor. Charles Darwin and the Theory of Evolution: Charles Darwin, in the 19th century, is credited with developing the theory of evolution by natural selection. His groundbreaking work, "On the Origin of Species" (1859), laid the foundation for modern evolutionary biology. Darwin's theory proposes that species change over time through a process of descent with modification. This means that new species arise from existing ones, and the diversity of life on Earth is the result of gradual changes occurring over long periods. Evolutionary Biology (Key Concepts) 1) Descent with Modification: Organisms share common ancestors and have descended with modifications from those ancestors. This concept underscores the unity of life on Earth. 2) Variation: Within populations, there is genetic variation, meaning individuals within a species can have different traits due to genetic mutations. 3) Natural Selection: The environment exerts selective pressures, favoring individuals with traits that increase their chances of survival and reproduction. These traits are passed on to the next generation. 4) Adaptation: Over time, the accumulation of advantageous traits leads to the adaptation of populations to their specific environments. Evolutionary Biology (Mechanisms of Evolution) Genetic Variation: Genetic mutations, genetic recombination during reproduction, and migration of individuals between populations contribute to genetic variation within species. Selection Pressure: Environmental factors, such as predation, climate, and resource availability, impose selection pressures that influence which traits are advantageous. Speciation: Over time, genetic changes can accumulate to the point where populations become distinct species. This is known as speciation. Evolutionary Biology (Evidence for Evolution) I. Fossil Record: Fossils provide important evidence for evolution and the adaptation of plants and animals to their environments. Fossil evidence provides a record of how creatures evolved and how this process can be represented by a 'tree of life', showing that all species are related to each other. 10  II. Comparative Anatomy: Similarities in the anatomical structures of different species, such as homologous structures (e.g., the limbs of humans, cats, whales, and bats), vestigial organs (e.g., in humans, include the appendix, the coccyx (tail bone), and the tonsils. Body hair, wisdom teeth, nipples on males, nictitating membrane of eye, tonsils are also the vestigial organs of humans), and embryonic development (a complicated process by which a fertilized egg develops into an embryo), reveal common ancestry. III. Molecular Biology: Genetic and molecular comparisons between species confirm their evolutionary relationships. DNA sequencing has been particularly valuable in this regard. IV. Biogeography: The distribution of species across the planet reflects historical patterns of migration and speciation. V. Experimental Evolution: Laboratory experiments with organisms like bacteria and fruit flies have demonstrated evolutionary processes in action. Figure 1: Evolution of humans Brief Summary Natural selection leads to slow and gradual change of organisms over successive generation Change in the heritable characteristics of biological populations over successive generations Poor adapted organisms perish while the well-adapted ones survive and hands on their beneficial traits to their offspring Nature selecting the fit and rejecting the unfit 11 Figure Lamarckism Jean-Baptiste Lamarck's theory of evolution, proposed in his book "Philosophie Zoologique" (1809), is based on the following key concepts: 1. Use and Disuse: The idea that traits are developed or lost based on their use or lack of use. 2. Inheritance of Acquired Characteristics: The notion that traits acquired during an individual's lifetime can be passed on to their offspring. 3. Progressive Evolution: The idea that evolution is a progressive, goal-oriented process, leading to increased complexity and perfection. While Darwinism is widely accepted as the foundation of modern evolutionary theory, Lamarckism has largely been discredited due to a lack of empirical evidence supporting its key concepts. However, both theories have contributed significantly to our understanding of evolution and the diversity of life on Earth. Introduction to Mendelian genetics and Laws of inheritance The foundation of modern genetics began by Gregor Johann Mendel (1822-1884) a German Czech Augustinian monk and scientist who studied the nature of inheritance in plants. Even though Mendel's work went largely unnoticed in his lifetime, he introduced the idea that traits are determined by paired units that he called "factors," now called "genes." He performed hybridization experiments with garden pea pisum sativm and formulated two fundamental laws of inheritance. Mendel tested all 34 varieties of peas available to him through seed dealers. The garden peas were planted and studied for eight years. Each character studied had two distinct forms, such as tall or short plant height, or smooth or wrinkled seeds. Mendel's experiments used some 28,000 pea plants 12 Some of Mendel's traits as expressed in garden peas. Laws of Inheritance Mendel proposed three laws: 1. Law of Dominance 2. The Law of Segregation 3. Law of independent assortment Law of Dominance: This law states that in a heterozygous condition, the allele whose characters are expressed over the other allele is called the dominant allele and the characters of this dominant allele are called dominant characters. The characters that appear in the F1 generation are called as dominant characters. The recessive characters appear in the F2 generation. The law of dominance is the first law of heredity proposed from the works of Mendel. The law explains that all characters in an individual are controlled by distinct units called factors that occur in pairs. The pair can be homozygous or heterozygous, and in the case of heterozygous pairs, one of the factors dominates the other. The character that dominates is called the dominant character, and the one that remains unexpressed is the recessive character. The recessive character, even though latent, is transmitted to the offspring in the same way as the dominant character. The recessive character is only expressed when the offspring has two copies of the same allele resulting in a homozygous individual. The two alleles responsible for a character are brought together during fertilization, where one of the alleles comes from the maternal gamete and the other from the parental gamete. 13  The concept of dominance is strictly only used for genotypic characters and does not represent the phenotype of the individual. With new experiments on genetics, many researchers believe that the law of dominance doesn’t always hold true and that other patterns of inheritance also exist. Characteristics of Mendel’s Law of Dominance The concept of dominance or the law of dominance originated from the concept of factors that transmit characters from the parents to the offsprings. Genes are the unit of inheritance that is transmitted via gametes that controls the expressions of different characters as a result of interaction with other genes. The genes occur within chromosomes which in the case of diploid cells occur in pairs. Each chromosome in the pair comes from a parent. Each of the contrasting characters is represented by an allele, resulting in two alleles for a pair of characters. Homozygous individuals have two identical alleles like the alleles TT in the case of the homozygous tall pea plant and tt in the case of the homozygous dwarf pea plant. The homozygous chromosomes are separated during gametogenesis so that the chromosome with T or t gene is passed to the gamete. During fertilization, the two gametes combine and produce a new individual with both the characters. The offspring is now called a heterozygote or hybrid as it contains two different genes for a pair of contrasting characters. The resulting hybrids all have tall stems, which indicate that the character of tallness is the dominant character and the dwarfness is recessive. 14 Limitations of Mendel’s Law of Dominance Mendel’s law of dominance has a number of limitations which are mentioned below: 1. The law is not applicable for all living organisms as it is only valid in the case of diploid organisms and the organisms that undergo sexual reproduction. 2. Even though dominance was considered the only mode of inheritance, a number of different modes like blending inheritance have since been discovered and studied. 3. Dominance also doesn’t occur in the case of all contrasting characters. 4. In some cases, conditions of co-dominance or incomplete dominance might take place. 15 Mendel’s Law of Segregation Mendel’s Law of Segregation states that ‘The hybrids or heterozygotes of F1 generation have two contrasting characters of dominant and recessive nature where the alleles though remain together for a long time do not contaminate or mix with each other and separate or segregate at the time of gametogenesis so that each gamete receives only one allele of a character either dominant or recessive.’ In simple words, the law states that only a single gene copy from a parent is distributed in a gamete, and the allocation of the gene copies is entirely random. Mendel’s law of segregation is based on a number of concepts; a gene exists in more than one form of an allele. during the formation of gametes, the allelic pair of a gene separate so that each gamete has a single allele. all organisms inherit two alleles for a genetic trait. the two alleles obtained for a trait are different as one is dominant and the other is recessive. The law of segregation enables the use of Punnett square for the estimation of resulting genotypes from a cross as it is based on the equal segregation of alleles. The law of segregation is significant as it introduced the concept of hereditary factors that remain as separate entities even when present together with other similar entities. The law was used to disprove a blending theory by the generation of traits encoded by recessive alleles in the F1 generation. 16 Law of Independent Assortment Mendel’s Law of Independent Assortment states that ‘when the parents differ from each other in two or more pairs of contrasting characters, the inheritance of one pair of characters is independent of the other.’ In simple words, the law states that all transfer of a particular character from parents to the offsprings remains unaffected by other characters. The law indicates that the alleles of different genes are assorted into the gametes independently of one another. Mendel’s work on dihybrid cross between different pea plants led to the discovery of this law as he observed that the combination of characters in the offspring did not always match that formed by the combination of the parental traits. The law explains the occurrence of a large number of combinations of genes from the same set of genes which couldn’t be explained previously. 17 18 Definitions of Key Genetic Terms. 1. Gene: A gene is an inherited factor which determines a biological characteristic of an organism. In diploid organisms, genes always occur in pairs. This pair is called alleles. 2. Alleles: These are the several alternative forms of a particular gene which occupy the same chromosomal locus. 3. Locus: This is the physical location of a particular gene along a chromosome. 4. Homozygous: This is used to describe an organism with two identical alleles for the same gene or at a given locus. 5. Heterozygous: This is used to describe an organism with two different alleles for the same gene or at a given locus. 6. Genotype: This is the genetic make-up of an organism with respect to one or more genes i.e. the genes the organism is carrying or the allelic composition of an organism. 7. Phenotype: This refers to the particular expression of a gene or to the sum of the traits which characterise an organism i.e., the appearance of the organism as a result of the genes it is carrying or the physical expression of the allelic composition for the trait under study 8. Trait: This is a particular feature shown as an expression of a gene. 9. Dominant: This is used to describe the gene or allele which can express itself under a homozygous or heterozygous condition a term applied to the trait (allele) that is expressed regardless of the second allele. 10. Recessive: This is used to describe the gene or allele which can express itself only under a homozygous condition or a term applied to a trait that is only expressed when the second allele is the same (e.g., short plants are homozygous for the recessive allele). 19 SELF ASSESSMENT EXERCISE 1. What are the three major components of the DNA? 2. List the FOUR (4) nitrogenous bases of the DNA. 3. List THREE types of RNA involved in protein synthesis. References 1. Elston R, Satagopan J, Sun S. Genetic terminology. Methods Mol Biol. 2012;850:1-9. doi:10.1007/978-1-61779-555-8_1 2. https://microbenotes.com/mendels-law-of-dominance/ 3. PowerPoint Presentations – Popoola on Genetics/BIO 101 – General Biology 1 2023. 20