BIO207H5S Introductory Genetics Winter 2024 Lecture 1 PDF

BIO207H5S Introductory Genetics Winter 2024 Lecture 1 Preeti Karwal, Ph.D. BIO207H5S LEC0101 Introductory Genetics Course Outline - Winter 2024 Instructor: Preeti Karwal E-mail Address: [email protected] Class Time and Location Mon, 01:00 PM - 02:00 PM, IB 110 Tue, 11:00 AM - 01:00 PM, I...

BIO207H5S Introductory Genetics Winter 2024 Lecture 1 Preeti Karwal, Ph.D. BIO207H5S LEC0101 Introductory Genetics Course Outline - Winter 2024 Instructor: Preeti Karwal E-mail Address: [email protected] Class Time and Location Mon, 01:00 PM - 02:00 PM, IB 110 Tue, 11:00 AM - 01:00 PM, IB 110 Office Hours Schedule and Location Monday 11:00 AM - 12:00 PM, DV3093CD Tuesday 1:00 PM - 2:30 PM, DV3093CD Textbooks: 1. 2. Pierce, Benjamin A. Genetics: A Conceptual Approach 7th ed. - W.H. Freeman & company, New York. Daniel L. Hartl. Genetics: Analysis of Genes and Genomes 9th Edition - Jones & Bartlett Publishers. The content covered in the lecture slides, classroom discussion and tutorials is the main source of information. Points of Contact for your Tutorials and Grading of Assessments TUT0106 and TUT0108: Eniolaye Balogun (Admin TA) E-mail Address [email protected] TUT0110, TUT0113, TUT0115 and TUT0117: Asawari Albal E-mail Address [email protected] TUT0105 and TUT0107 : Neha Purakan E-mail Address [email protected] TUT0101 and TUT0103: Nicholas Boehler E-mail Address [email protected] TUT0109 and TUT0111 : Farhan Majumder E-mail Address [email protected] TUT0102 and TUT0104 : Timothy McLean E-mail Address [email protected] TUT0114 and TUT0116 : Yijie (Jacky) Zhu E-mail Address [email protected] TUT0112: Farheen Mohammed E-mail Address [email protected] Grading TA: Cameron Sinclair E-mail Address [email protected] Tutorial Quizzes - There will be weekly tutorial quizzes. The Lowest quiz mark will be dropped. Participation in all tutorial quizzes is highly recommended as NO makeup quizzes will be taken in any circumstances. Final Exam - The final Exam is CUMULATIVE, it covers all the content covered during lectures and tutorials. The Final exam, like the term tests, will likely include multiple choice, short answer and few long answer subjective type questions. (more details will be shared on Quercus before the final exam). Term Tests The Term Tests are NOT cumulative and will cover all material covered before or in between two term tests. There will be 3 term tests and the two highest-scored term tests will count toward your final grade. Participation in all three tests is highly recommended as NO retests or makeup tests will be taken in any circumstances. If you miss a term test, use the Absence Declaration tool on ACORN to declare an absence and contact your instructor. In case of two missed tests due to unforeseen circumstances, a weighted average based on the redistribution of grades for other similar assessments will be considered subject to evaluation of individual case based on the timely submission of appropriate documents for proof of your reason for absence. For this academic consideration, the student will be required to submit appropriate documentary proof of their reason for absence e.g., medical documentation to Eniolaye Balogun, the admin TA within two days of their absence in the term test. This redistribution of grades, if at all considered will apply to only one of the two essential term tests, not both. Genetics Genetics is the study of heredity, how inherited variation is encoded, replicated, and expressed, and how it evolves over time. This definition encompasses the three major subdivisions of genetics: transmission genetics, molecular genetics, and population genetics. 1.6 Genetics can be divided into three major subdisciplines 1.7 Model genetic organisms are species with features that make them useful for genetic analysis TABLE 1.1 Early concepts of heredity Concept Proposed Correct or Incorrect Pangenesis Genetic information travels from different parts of the body to reproductive organs. Incorrect Inheritance of acquired characteristics Acquired traits become incorporated into hereditary information. Incorrect Preformationism Miniature organism resides in sex cells, and all traits are Table 1.1 Early concepts of heredity inherited from one parent. Incorrect Blending inheritance Genes blend and mix. Incorrect Germ-plasm theory All cells contain a complete set of genetic information. Correct Cell theory All life is composed of cells, Correct and cells arise only from cells. Mendelian inheritance Traits are inherited in accord with defined principles. Correct Father of Genetics Gregor Johann Mendel 1822–1884 Why do you think Mendel was successful? Mendel’s Skills ▪ He adopted an experimental approach unlike many earlier investigators who simply described the results of crosses. He formulated hypotheses based on his initial observations and then conducted additional crosses to test his hypotheses. ▪ He always interpreted his results by using mathematics. He kept careful records of the numbers of progeny possessing each trait and computed ratios of the different traits. ▪ He was adept at seeing patterns in detail and was patient and thorough, conducting his experiments for 10 years before attempting to write up his results in 1866. Advantages from the Model Organism and the Experimental Setup ▪ Garden pea plants complete entire generation in a single growing season (annual plants) and produce many offspring. ▪ Garden pea plants are known to differ in detectably distinct characters. e.g., seed colour, seed shape, flower colour, pod colour, texture. ▪ Pea plants are self fertilizing plants – True breeding lines. Also artificial cross-pollination was possible. ▪ The loci for any two characters studied simultaneousy in a dihybrid cross were located far apart in most cases – Independent assortment. ▪ In Mendel’s peas, the genotype and not the environment, largely determined the characters. Some more facts about Mendel…… Mendel did these experiments about 20 years before microscopy advances allowed identification of chromosomes and their role in inheritance. He published his work in 1866 but his work went unappreciated for about 34 years. Hugo de Vries, Erich Tschermark and Carl Correns independently confirmed Mendel’s conclusions around year 1900. The theory that genes are located on chromosomes (the chromosomal theory of heredity) was developed in the early 1900s by Sutton and Boveri. 3.5 (1) Mendel conducted monohybrid crosses Monohybrid cross Mendel began by conducting monohybrid crosses, the crosses between parents that differed in a single characteristic. Principle of Segregation Mendel drew several conclusions from the results of his monohybrid crosses 1. He reasoned that although the F1 plants display the phenotype of only one parent, they inherit genetic factors from both parents as both parental phenotypes are seen in F2 generation. Each plant must therefore possess two genetic factors encoding a characteristic. 2. The two alleles in each plant separate when gametes are formed, and one allele goes into each gamete. 3. The traits that appeared unchanged in the F1 heterozygous offspring Mendel termed as dominant, and those that disappeared in the F1 heterozygous offspring were named as recessive. The Concept or Law of Dominance states that when two different alleles are present in a genotype, only the trait encoded by one of them—the dominant allele—is observed in the F1 phenotype. 4. The two alleles of an individual plant separate with equal probability into the gametes. All these four conclusions formed the basis of Principle of segregation (Mendel’s first law). “This principle states that each individual possesses two alleles (diploid organism) for any particular trait, one inherited from the maternal parent and one from the paternal parent. These alleles segregate from each other at the time of gamete formation.” Mendel further confirmed the Principle of Segregation by allowing the F2 plants to self-fertilize and produce an F3 generation. TABLE 3.1 Summary of important genetic terms Term Definition Gene An inherited factor (encoded in the DNA) that helps determine a characteristic Allele One of two or more alternative forms of a gene Locus Specific place on a chromosome occupied by an allele Genotype Set of alleles possessed by an individual organism Table 3.1 Homozygote An individual organism possessing two of the same alleles at a locus Heterozygote An individual organism possessing two different alleles at a locus Characteristic or character An attribute or feature possessed by an organism Phenotype or trait The appearance or manifestation of a characteristic Molecular basis of Mendelian law of Segregation 3.7 Segregation results from the separation of homologous chromosomes in meiosis TABLE 3.2 Comparison of the principles of segregation and independent assortment Principle Observation State of Meiosis* Segregation (Mendel’s first law) 1. Each individual organism possesses two alleles encoding a trait. Before meiosis 2. Alleles separate when gametes are formed. Anaphase I Table 3.2 3. Alleles separate in equal proportions. Anaphase I Alleles at different loci separate independently. Anaphase I Independent assortment (Mendel’s second law) *Assumes that no crossing over occurs. If crossing over takes place, then segregation and independent assortment may also occur in anaphase II of meiosis. Punnet Square can be used to calculate the results of genetic crosses The Punnett square is a shorthand method of predicting the genotypic and phenotypic ratios of progeny from a genetic cross. This method was developed by the English geneticist Reginald C. Punnett in 1917. A Punnett square is constructed by drawing a grid, listing the gametes produced by one parent along the upper edge, and listing the gametes produced by the other parent down the left side. By crossing two varieties of pea plants that differed in height, Mendel established that tall (T) was dominant to short (t). He tested his theory concerning the inheritance of dominant traits by crossing an F1 tall plant that was heterozygous (Tt) with the short homozygous parental variety (tt). Backcross The type of cross, between an F1 genotype and either of the parental genotypes, is called a backcross. A type of backcross is testcross. Testcross The cross in which one individual of unknown genotype is crossed with another individual with a homozygous recessive genotype for the trait in question. Application: A testcross helps to test or reveal the genotype of the first individual. A Phenotypic ratio of 1:1 in F1 generation resulting from a test cross is characteristic of a heterozygous genotype of the individual tested. Another method for determining the outcome of a genetic cross is to use the rules of probability, as Mendel did with his crosses. Probability refers to the likelihood of the occurrence of a particular event. It is the number of times that a particular event takes place, divided by the number of all possible outcomes. Probability values range from 0 to 1. Two rules of probability are useful for predicting the ratios of offspring from genetic crosses: 1. Addition or Sum rule P (A or B) = P (A) + P (B) 1. Multiplication or Product rule P (A and B) = P (A) X P (B) Genotype TT or Tt or tT Possible gametes Probability Phenotype ¼+¼+¼=¾ tall Dihybrid cross In addition to his work on monohybrid crosses, Mendel performed crosses in which the varieties of peas differed in two characteristics, called dihybrid crosses. 3.11c Mendel’s dihybrid crosses revealed the principle of independent assortment Principle of Independent Assortment Mendel carried out a number of dihybrid crosses for pairs of characteristics and always obtained a 9 : 3 : 3 : 1 ratio in the F2. 9 : 3 : 3 : 1 ratio makes perfect sense in regard to the principle of segregation and the concept of dominance. Mendel recognized in the results of dihybrid crosses, the principle of independent assortment (Mendel’s second law). “This principle states that alleles at different loci separate independently of one another.” The principle of independent assortment is an extension of the principle of segregation as it states that when the two alleles separate at a locus, their separation is independent of the separation of alleles at other loci. Molecular basis of Mendelian law of Independent Assortment 3.12 The principle of independent assortment results from the independent separation of chromosomes in anaphase I of meiosis