Genetics Handout PDF

Genetics - Handout Genetics  The term Genetics was introduced by Bateson in 1906. It was derived from Greek word "Genno" which means 'to become' or 'to grow into'.  The branch of biology that deals with the study of heredity, or the passing of traits from parents to offspring.  The fund...

Genetics - Handout Genetics  The term Genetics was introduced by Bateson in 1906. It was derived from Greek word "Genno" which means 'to become' or 'to grow into'.  The branch of biology that deals with the study of heredity, or the passing of traits from parents to offspring.  The fundamental unit of heredity is a gene. Genetics Personalities  Gregor Mendel - Father of Genetics. He is an Austrian monk. Through his experiments on pea plants (Pisum sativum), he discovered the fundamental laws of inheritance  William Bateson - coined the term "Genetics". Bateson introduced the term "genetics" in 1905 to describe the study of heredity and variation. Bateson was instrumental in the revival of Mendelian genetics. He recognized the significance of Gregor Mendel's work on inheritance patterns and helped to promote and validate Mendel’s theories through his own research and publications ("Mendel's Principles of Heredity: A Defence" (1902) and "Problems of Genetics" (1907))  Imre Festetics (Count Imre Festetics of Tolna) - a Hungarian noble landowner, sheep breeder, and a pioneer geneticist, formulated several rules of heredity that he referred to as the “genetic laws of nature”. Festetics empirically deduced that organisms inherit their specific characteristics rather than acquiring them. Festetics also emphasize the reappearance of traits wherein traits of grandparents that differ from those of immediate progeny may reappear in later generations.  Wilhelm Johannsen - introduced the terms "gene," "genotype," and "phenotype" in his book "Elemente der exakten Erblichkeitslehre" ("Elements of the Exact Science of Heredity"). Gene: He used this term to describe the hereditary units that carry information from one generation to the next. Genotype: This term refers to the genetic constitution of an organism. Phenotype: This term refers to the observable characteristics or traits of an organism, which result from the interaction of the genotype with the environment. - Johannsen's experiments with beans led to the formulation of the pure line theory, which demonstrated that the observed variation in a population could be partitioned into genetic and environmental components. He showed that selection within pure lines (genetically uniform lines) does not lead to further genetic changes, emphasizing the stability of the genotype. Terminologies  Alleles - alternative forms or versions of a gene that occupy a specific position, called a locus, on a chromosome; may be identical (homozygous) or different (heterozygous), and they determine the traits or characteristics of an organism.  Autosomal Chromosome - non-sex chromosomes; Humans (22 pairs of autosomes); carry genes responsible for various bodily functions and traits, excluding those related to sex determination.  Biotechnology - use of biological systems, organisms, or derivatives to develop or create products and technologies for various applications  Chromatid - one of the two identical copies of a replicated chromosome, which are joined at the centromere.  Chromatin - It is a relaxed state of chromosome with protein Histone.  Chromosome - thread-like structure composed of DNA and proteins found in the nucleus of most living cells; carry genetic information in the form of genes and are essential for the transmission of hereditary traits during cell division  Dihybrid - refers to a genetic cross involving two traits  Dominant - one that is expressed when present in either the heterozygous (having two different alleles) or homozygous (having two identical alleles) state; mask the expression of recessive alleles in heterozygous individuals.  Gene - a segment of DNA that contains the instructions for building and maintaining an organism; serve as the basic units of heredity and areresponsible for transmitting traits from one generation to the next.  Genetics - It is the branch of biology that deals with heredity.  Genotype - It is the genetic make-up of an organism (represented by the letters).  Heterozygous - refers to an individual or organism that has two different alleles for a particular gene; one allele is dominant, and the other is recessive.  Homologous Chromosome - chromosome pairs, one from each parent, that carry the same genes at the same loci.  Homozygous - refers to an individual or organism that has two identical alleles for a particular gene; can be for either the dominant or recessive allele.  Karyotype - a visual arrangement of a complete set of chromosomes from an organism. It shows the number, size, and shape of chromosomes arranged in pairs according to their size and the position of the centromere. Often used for studying chromosomal abnormalities and genetic disorders.  Locus - refers to the specific physical location of a gene or other DNA sequence on a chromosome  Monohybrid - refers to a genetic cross involving one trait  Pedigree - It is a graphic organizer to map genetic traits between generations.  Phenotype - observable physical or biochemical characteristics of an organism, resulting from the expression of its genes as well as the influence of environmental factors  Polygenic Inheritance - refers to the inheritance of traits that are controlled by multiple genes. Polygenic traits often exhibit a continuous variation, meaning there is a spectrum of phenotypes (e.g., height, skin color, eye color).  Punnett Square - a graphical representation used in genetics to predict the possible outcomes of a genetic cross between two individuals  Recessive - one that is expressed only when present in a homozygous condition  Sex-linked Genes - genes located on the sex chromosomes (X or Y); Traits controlled by these genes often exhibit different inheritance patterns in males and females due to the difference in the number of X chromosomes.  Sister Chromatid - two identical copies of a replicated chromosome; held together by a centromere and are produced during the S phase of the cell cycle when DNA is replicated  Test Cross - genetic cross used to determine the genotype of an individual expressing a dominant phenotype Mendelian Laws of Genetics  Johann Gregor Mendel - Austrian monk, born in Czech Republic in 1822  He worked at monastery and taught high school.  He grew peas at the monastery garden and became interested in the traits that were expressed in different generations of peas. He formulated the principle of inheritance.  Reasons why Mendel used pea plants on his experiment: Distinct Traits: Pea plants have several easily observable traits, such as flower color, seed shape, and plant height. These traits come in clear-cut forms (like purple or white flowers), making it easier to track inheritance patterns.  Controlled Pollination: Pea plants can be self-pollinated (where pollen from the same plant fertilizes its own eggs) or cross-pollinated (where pollen from one plant fertilizes another plant's eggs). This flexibility allowed Mendel to control and manipulate his experiments more effectively. Short Generation Time: Pea plants grow and reproduce quickly, which allowed Mendel to observe multiple generations in a relatively short period.  Mendel focused on seven pairs of contrasting traits of the pea plant on his experiment: Flower color (purple or white) Flower position (axial or terminal) Seed color (yellow or green) Seed shape (round or wrinkled) Pod color (green or yellow) Pod shape (inflated or constricted) Plant height (tall or short)  Mendel’s Experiment on Pea plants (Monohybrid Cross) P Generation (Parental Generation): Mendel started with true-breeding plants for each trait. For example, he crossed a true-breeding tall plant (TT) with a true-breeding short plant (tt). True-breeding plants (homozygous) for each trait were used (e.g., TT for tall and tt for short). F1 Generation (First Filial Generation): All offspring (F1 generation) from this cross were heterozygous (Tt) and exhibited the dominant trait (tall). There were no short plants in the F1 generation. F2 Generation (Second Filial Generation): Mendel allowed the F1 generation plants to self- pollinate. The resulting F2 generation displayed both tall and short plants in a 3:1 ratio (three tall plants for every one short plant). Results and Conclusion  Mendel concluded that traits are inherited as discrete units (now called genes).  Each individual has two alleles for each trait, one inherited from each parent.  The alleles segregate during the formation of gametes (Law of Segregation).  The dominant allele masks the expression of the recessive allele in the heterozygous condition.  Mendel’s Experiment on Pea plants (Dihybrid Cross) P Generation (Parental Generation): Mendel crossed true-breeding plants with two different traits. For example, he crossed a plant with yellow round seeds (YYRR) with a plant with green wrinkled seeds (yyrr). F1 Generation (First Filial Generation): All F1 offspring were heterozygous for both traits (YyRr) and exhibited the dominant traits (yellow and round). F2 Generation (Second Filial Generation): Mendel allowed the F1 generation plants to self-pollinate. The resulting F2 generation displayed four different combinations of traits: yellow round, green round, yellow wrinkled, and green wrinkled. The observed phenotypic ratio was 9:3:3:1.  Results and Conclusion  Mendel concluded that different traits are inherited independently of one another (Law of Independent Assortment).  This law applies to genes located on different chromosomes or far apart on the same chromosome, allowing them to assort independently during gamete formation.  Law of Dominance - This law states that the dominant allele will prevent the recessive allele from being expressed in men. If an individual has a genotype (Aa), and allele A is dominant while allele a is recessive, the dominant allele A will determine the observable trait in the phenotype.  Law of Independent Assortment - states that alleles of different genes segregate independently of each other during gamete formation. In other words, the inheritance of one gene does not influence the inheritance of another gene.  Law of Segregation - states that anindividual has two alleles for each gene, one inherited from each parent. Non-Mendelian Laws of Genetics  While Mendel's laws provide a foundational understanding of genetic inheritance, some genetic phenomena do not strictly follow these classical principles.  Incomplete Dominance - Neither allele is completely dominant over the other, resulting in a blend of the two traits. The traits blend together producing an intermediate phenotype. In flowers, a cross between red-flowered (RR) and white-flowered (rr) plants results in pink- flowered (Rr) offspring.  Codominance - Both alleles are expressed equally in the phenotype. In roan cattle,a cross between red cattle and white cattle results in cattle with coat consists of a mix of red and white hairs.  Multiple Alleles - A gene is controlled by multiple alleles. For example, the ABO blood group system in humans involves three alleles (IA, 1B, i), determining the A, B, and o blood types. Universal blood donor: Blood type O- Universal blood recipient: Blood type AB+  Pleiotropy - One gene affects multiple characteristics. A single gene has multiple effects on an organism’s phenotype. Mutation  It is a change in genetic code  Changes in the DNA sequence of an organism maybe due to UV radiation, exposure to certain chemicals, errors during DNA replication, etc.  It is transmitted to offspring if occurs in sex cells  Types of Mutations and Their Heritability Germline Mutations: Mutations that occur in the reproductive cells (sperm or eggs). These mutations can be passed on to offspring because they are present in the DNA of the gametes that combine during fertilization. Somatic Mutations: Mutations that occur in non-reproductive cells (somatic cells) during an individual’s life. These mutations are not passed to offspring because they are not present in the gametes. They can, however, affect the individual’s health and may lead to diseases like cancer.  Causes of Mutation Internal Mutation: this is the mutation type that can be observed most of the time. Internal mutations originate from processes or errors within the organism, such as DNA replication mistakes.  External Mutation - this is a very rare type of mutation process. In this process, there is no role in the DNA replication process. Rather than, some chemicals or agents inserted into the human body from the outside. And they started reacting on the DNA sequences.  Types of Mutation Gene Mutation - change in a single gene  Substitution - During replication, one base is inserted erroneously, replacing the pair in that location on, the complementary strand.  Ex. Sickle cell anemia  Sickle cell anemia is a genetic disorder characterized by the production of abnormal hemoglobin, which leads to the distortion of red blood cells into a sickle shape.  Insertion - In replicating DNA, one or more extra nucleotides are added, frequently causing a frameshift.  Ex. A form of beta-thalassemia  Beta-thalassemia is a genetic blood disorder characterized by the production of abnormal hemoglobin due to mutations in the beta- globin gene. This leads to reduced or absent production of beta-globin chains, which are crucial components of hemoglobin.  Deletion - One or more nucleotides is skipped during replication or otherwise excised, often resulting to a frameshift.  Ex. Cystic fibrosis  Cystic Fibrosis (CF) is a genetic disorder caused by deletions in the CFTR gene (Cystic Fibrosis Transmembrane Conductance Regulator), which leads to the production of a defective CFTR protein. Chromosome Mutation - change in many genes. Can be spontaneous or caused by environmental mutagens (radiation, chemicals, etc.)  Inversion - A chromosome's one section is turned around and reinserted. Chromosome inversion is a type of structural chromosomal mutation where a segment of a chromosome breaks off, flips around, and reattaches in the reverse orientation. This change can affect the genes within the inverted segment, potentially leading to various genetic effects.  Deletion - When a chromosome segment is lost, all the genes in that segment are also gone  Ex. Cri du chat (5p- deletion)  Cri du Chat Syndrome (also known as "Cry of the Cat Syndrome") is a genetic disorder caused by a deletion of a portion of chromosome 5. The name comes from the distinctive cry of affected infants, which sounds like a cat meowing.   Duplication - Repeating a section of a chromosome increases the dosage of the genes in that section  Ex. Charcot- Marie-Tooth disease  Charcot-Marie-Tooth Disease Type 1A (CMT1A) is caused by a duplication of the PMP-22 gene on chromosome 17, leading to progressive weakness, sensory loss, and gait issues due to damage to peripheral nerves.  Translocation - A section of one chromosome is abnormally joined to another  Ex. Cancer (lymphoma and leukemia) Missense - Nucleotide change leads to amino acid change (most common C to T). A missense mutation is a type of mutation in DNA where a single nucleotide change results in the substitution of one amino acid for another in a protein. Nonsense - Change leads to stop codon. A nonsense mutation is a type of mutation in DNA that introduces a premature stop codon into the mRNA sequence. This mutation causes the protein to be truncated, meaning it ends earlier than it should. Splice site - Changes RNA splicing. A splice site mutation is a type of genetic mutation that affects the normal splicing process of pre-mRNA (precursor mRNA) during the conversion to mature mRNA. This type of mutation can disrupt the normal removal of introns (non-coding regions) and the joining of exons (coding regions), potentially leading to the production of abnormal proteins. Genetic Disorders  Hemophilia - It is a genetic disorder that causes your blood to cloth less. This condition can lead to excessive bleeding, even from minor injuries, and can cause spontaneous bleeding into joints and muscles.  Phenylketonuria - It is an inherited disorder that can lead to excessive production of amino acid phenylalanine in the blood which is toxic to the nervous system that can cause intellectual disorder.  Sickle Cell Anemia - It is a disease caused by inheriting 2 faulty hemoglobin genes known as hemoglobin S. People who suffer this disease die due to constant shortage of red blood cells.  Down Syndrome - It is known as Trisomy 21, an additional one copy of chromosome in chromosome no. 21. A total of 47 chromosomes.  Edward’s Syndrome (Trisomy 18) - a genetic disorder caused by the presence of an extra chromosome 18 in some or all of the body's cells.  Patau Syndrome (Trisomy 13) - a genetic disorder caused by the presence of an extra chromosome 13 in some or all of the body's cells.  Klinefelter Syndrome - It is a genetic disorder where a male has an extra copy of X chromosome in chromosome 23; XXY.  Turner Syndrome - It only affects females. In chromosome 23 of female, one X chromosome is missing or partially missing; XO.  Cri-Du-Chat Syndrome ( 5p- syndrome) - a rare genetic disorder caused by a deletion of a portion of chromosome 5. The name "cri-du-chat" is French for "cry of the cat," referring to the distinctive high-pitched cry that affected infants make, which resembles the mewing of a cat.  Prader-Willi Syndrome - a complex genetic disorder that typically results from the absence of expression of paternal genes in a specific region of chromosome 15.  Wolf-Hirschhorn Syndrome - a rare genetic disorder caused by a deletion on the short arm of chromosome 4  Fragile X Syndrome - a genetic condition caused by a mutation in the FMR1 gene, located on the X chromosome. This mutation leads to a deficiency or absence of the FMRP (Fragile X Mental Retardation Protein), which is necessary for normal brain development.  Trisomy X - a genetic condition in which females have an extra X chromosome, resulting in a total of three X chromosomes instead of the typical two.  XYY Syndrome (Jacob's syndrome) - a genetic condition that occurs when a male has an extra Y chromosome in each of their cells, resulting in a total of 47 chromosomes instead of the typical 46. Genetic Engineering  It is the process of using DNA (rDNA) technology to alter the genetic makeup of an organism.  It is sometimes called biotechnology.  Example is insulin produced by bacteria  Oil-eating bacteria is used for bioremediation.  It has applications in medicine, environment, industry, agriculture, and selective breeding.  Process involved in Genetic Engineering Identify the section of DNA that contains required gene from the source chromosome. Extract the required gene. Bacterial plasmid is removed from the bacterial cell and cut open using enzymes. Insert plasmid into host cell and sealed using enzyme. Grow transformed cells to produce a genetically modified organism (GMO)  Applications of Genetic Engineering Distant Hybridization  The invention of genetic engineering has made it possible to transfer genes between species that are only distantly related. Higher creatures can receive desired genes from smaller organisms.  involves crossing closely related but sexually incompatible species to introduce desirable traits from one species into the genetic background of another.  Example: Dianthus caryophyllus barbatus also known as Fairchild's Mule - A crossbred of a carnation pink (Dianthus caryophyllus) and Sweet William (Dianthus barbatus) Development of Transgenic Plants  Transgenic plants are genetically modified organisms (GMOs) that have had genes from other organisms (often unrelated species) introduced into their genome.  Includes traits like resistance to pests or diseases, tolerance to herbicides, improved nutritional content, and enhanced shelf life.  Example: Bt Corn (Bacillus thuringiensis corn) - A type of genetically modified (GM) corn that has been engineered to produce a protein derived from the soil bacterium Bacillus thuringiensis (Bt)   Example: Bt Cotton - A type of genetically modified (GM) cotton that has been genetically engineered to produce proteins from the bacterium Bacillus thuringiensis (Bt).  Example: Golden Rice - A genetically modified (GM) rice variety that has been developed to address vitamin A deficiency. Golden rice was engineered to produce beta-carotene, a precursor of vitamin A.  Example: Flavr Savr Tomato - First recognized genetically modified organism (GMO) created through genetic engineering. First GMO approved for commercial production and consumption. Genetically modified to reduce the production of the enzyme polygalacturonase, which softens the fruit as it ripens Development of Root Nodules in Cereal Crops  Leguminous plants' root- nodules contain Rhizobium, a type of bacteria that fixes nitrogen. Rhizobium transforms free atmospheric nitrogen into nitrates in the root nodules.  Genetic engineering aims to extend the nitrogen-fixing capability to non-leguminous plants, such as cereals like rice, which are typically poor at fixing nitrogen.  Example: Biological Nitrogen Fixation (BNF) Rice - Biological Nitrogen Fixation (BNF) in rice refers to efforts to introduce or enhance the ability of rice plants to fix nitrogen from the atmosphere with the help of symbiotic bacteria, similar to how legumes like soybeans form root nodules with rhizobia bacteria. Development of C4 Plants  C4 plants are characterized by a modified carbon fixation pathway that enhances photosynthetic efficiency, particularly in high- temperature and arid conditions.  Genetic engineering is employed to introduce C4 photosynthetic pathways into C3 plants (conventional plants with the standard photosynthetic pathway).  Examples: Sorghum, sugarcane, maize, and some grasses which are grown in tropical and subtropical zones. Production of Antibiotics  Genetic engineering is employed to enhance the production of antibiotics by microorganisms such as bacteria and fungi  Through genetic modification, strains of bacteria or fungi can be engineered to produce higher yields of antibiotics.  Example: Tetracycline which is a broad- spectrum naphthacene antibiotic produced semi synthetically from chlortetracycline, an isolated antibiotic from bacterium Streptomyces aureofaciens. Production of Hormone Insulin  Genetic engineering allows for the production of human insulin using recombinant DNA technology.  By inserting the human insulin gene into bacteria or yeast, these microorganisms can be engineered to produce insulin that is identical to the one naturally produced by humans.  Example: The first human insulin produced using recombinant DNA technology is known as Humulin. It was developed by Genentech and Eli Lilly and Company and was the first synthetic "human" insulin approved for therapeutic use. Production of Vaccines  Genetic engineering facilitates the development and production of vaccines by manipulating the genetic material of organisms.  A vaccine can be created by transferring antigen-coding genes to disease-causing microorganisms. The hosts are shielded from infection by the same bacterium or virus by the antibodies.   Example: Inactive polio vaccine (IPV) is an example of a vaccine for polio. IPV contains poliovirus that has been inactivated (killed) so it cannot cause disease. It is designed to stimulate an immune response without causing the disease itself.  Four ways to make vaccines:  Inactivated or Killed Vaccines: These vaccines use viruses or bacteria that have been killed or inactivated so they cannot cause disease.  Live Attenuated Vaccines: These vaccines contain live viruses or bacteria that have been weakened so they cannot cause illness in healthy people.  Subunit, Recombinant, or Conjugate Vaccines: These vaccines include only parts of the virus or bacteria, such as proteins or sugars, rather than the whole organism.  mRNA Vaccines: These vaccines use messenger RNA (mRNA) to instruct cells to produce a protein that triggers an immune response. The mRNA is not infectious but teaches the body to recognize and fight the actual virus if it is encountered. Diagnosis of Disease  Genetic engineering plays a role in the development of diagnostic tools for detecting genetic disorders and diseases.  Recombinant DNA allowed doctors to diagnose several disorders.  Examples: Nucleic Test, Acid Antigen/Antibody Test and Antibody Test are types of tests conducted detect HIV.  Nucleic Acid Tests (NATs): Detects the actual virus (HIV RNA or DNA) in the blood.  Antigen/Antibody Tests: Detects both HIV antibodies and antigens (specifically the HIV p24 antigen).  Antibody Tests: Detects antibodies produced by the immune system in response to HIV. Production of Enzymes  Genetic engineering is employed to produce enzymes for various industrial and medical applications.  The production of useful enzymes using recombinant DNA technology is possible. One such enzyme is urokinase, which is used to break up blood clots. It was created by microbes that were genetically modified. Production of Transgenic Animals  Genetic engineering allows for the introduction of foreign genes into the genome of animals.  Preferred genes are inserted into an animal in order to create transgenic animals. This technique contributes to the diversification of animal selective breeding Additionally, it guarantees the production of better farm animals for commercially viable advantages.  Example: Dolly the sheep was the first transgenic animal. She was the first mammal to be cloned from an adult somatic cell. Born on July 5, 1996, at the Roslin Institute in Scotland, Dolly was a Finn-Dorset sheep.  Other Applications of Biotechnology Stem Cell - It is applied to fix damaged or defective tissue. Gene Therapy - It is intended to inject genetic material into cells in order to replace dysfunctional genes, fix mutations, or produce a useful protein. In Vitro Fertilization - This biotechnology describes the extema fertilization of an egg cell by a sperm cell. The consequence of fertilization is what are referred to as "test tube babies." Cloning - This biotechnology tries to duplicate DNA or any other necessary biological material without requiring a person to surrender their priceless biological being for the benefit of another person.  Human Genome Sequence - Finding the order of nucleotide base pairs that make up the entire human DNA is the goal of a worldwide scientific research initiative. Human Genome Project  first recognize the successful sequencing of all genes in human body  Launched in October 1990 and completed in April 2003  an international research effort that aimed to identify and map all the genes in the human genome, the complete set of DNA in the human organism  Objectives of the Human Genome Project To determine the complete sequence of the human DNA (genome). To identify all the genes in the human genome To understand the function of genes and their roles in health and disease. To develop new technologies and methods for genomic research.