TMJC Inheritance Notes

Page 1 of 75 Tampines Meridian Junior College JC2 H2/9744 Biology 2024 11. Genetics & Inheritance (VIII) – Inheritance SYLLABUS OVERVIEW No. Overarching Idea Topics 1 Core Idea 1 The Cell and Biomolecules of Life Cell – The Basic Unit of Life 2 Biomolecules of Life and Cellular Transport 3 Core Idea 3 Energy and Equilibrium Transformation of Energy – Photosynthesis and Cellular Respiration 4 Core Idea 2 Genetics and Inheritance Genetics and Inheritance (I) – The Cell Cycle 5 Genetics and Inheritance (II) – DNA Replication and Gene Expression 6 Genetics and Inheritance (III) – DNA Mutations and their Consequences 7 Genetics and Inheritance (IV) – Molecular Techniques in DNA Analysis 8 Genetics and Inheritance (V) – Organization of Genome & Control of Gene Expression in Eukaryotes [Includes Core Idea 1D: Stem Cells] 9 Genetics and Inheritance (VI) – Organization and Inheritance of Viral Genomes 10 Genetics and Inheritance (VII) – Organization of Genome & Control of Gene Expression in Prokaryotes 11 Genetics and Inheritance (VIII) - Inheritance 12 Core Idea 3 Energy and Equilibrium Communication and Equilibrium in Multicellular Organisms 13 Core Idea 4 Biological Evolution Biological Evolution 14 Extension Topic A Infectious Diseases Immunity and Infectious Diseases 15 Extension Topic B Impact of Climate Change on Animals & Plants Climate Change – Causes and Impacts on Animals and Plants

Biology Unit, Tampines Meridian JC Page 2 of 75 TOPIC SYNOPSIS An understanding of Genetics and Inheritance that would help make sense of the transition from molecular to organismal level. Genetics and Inheritance provides the molecular basis to the understanding of how variations in populations arise and this is important in the study of biological evolution. At the cellular level, expression of genes involves cellular structures such as the nucleus, endoplasmic reticulum and ribosome. Many essential products of gene expression are enzymes involved in biochemical pathways which control physiological functions. As such, mutation of genes may give rise to dysfunctional proteins which in turn could result in diseases. Sickle cell anemia and cancer are raised as examples of a monogenic and a mul ti- genic disease respectively. The following questions should help students frame their learning: • How does the genetic make -up of an organism and the environment influence the organism’s appearance, behavior and survival? • How does the inheritance of genetic information ensure the continuity of human as a species? Mutation arises from imperfect replication of genetic information; together with other biological processes, such mutations increase genetic variation Mutation, meiosis and sexual reproduction give rise to genetic variation within a population. Besides these, environmental factors are known to influence the phenotype of organisms. There are two kinds of genetic variations: continuous variation involves many genes, which have an addictive effect in controlling a characteristic; discontinuous variation involves one or just a few genes in controlling a characteristic. Besides these, environmental factors are known to influence the phenotype of organisms. Expression of genes gives rise to functional products that affect biochemical reactions and physiological functions of organisms. This demonstrates how the genotype and phenotype of an organism are related. Besides its genotype, the environment also plays a role in determining the phenotype of an organism and this is related to the field of epigenetics. Some environmental factors include availability of nutrients and changes in temperature. The chromosomal basis of inheritance sheds light on the pattern of transmitting genes from parents to offspring When Gregor Mendel first started his investigations into inheritance, the concept of genes had not been used. He used the term ‘traits’ in place of genes. By using genetic diagrams, the phenotypic and genotypic ratios of filial generations can be predicted for crosses involving monohybrid or dihybrid inheritance. In line with Mendelian genetics, pedigree diagrams can be used to predict the probability of inheriting genetic diseases, such as haemophilia and Huntington’s disease. Non-Mendelian inheritance involves more complex traits. For example, alleles of some genes exhibit co - dominance or incomplete dominance and some genes have multiple alleles or are found on the sex chromosomes. Furthermore, phenotypes may depend on interactions between two or more genes, e.g. epistasis. In addition, inheritance of linked genes does not follow Mendelian laws; in predicting the phenotypic and genotypic ratios of filial generations for linked genes, the occurrence and frequency of crossing over has to be considered.

Biology Unit, Tampines Meridian JC Page 3 of 75 LEARNING OUTCOMES Core Idea 2F: Inheritance This concept includes both Mendelian and non-Mendelian inheritance. Besides genetics, the environment also plays a role in determining the phenotype of an organism. Statistical tests, such as the chi -squared test, allow scientists to test the significance of differences between observed and expected results of genetic crosses. Candidates should be able to: a) Explain the terms: locus, allele, dominant, recessive, codominant, incomplete dominance, homozygous, heterozygous, phenotype, genotype and linkage. b) Explain how genes are inherited from one generation to the next via the germ cells or gametes. c) Explain how genotype is linked to phenotype. d) Use genetic diagrams to solve problems in dihybrid crosses, including those involving codominance, incomplete dominance, multiple alleles, sex linkages, autosomal linkage and epistasis. e) Use genetic diagrams to solve problems involving test crosses. f) Explain the meaning of the terms linkage and crossing -over and explain the effect of linkage and crossing over on the phenotypic ratios from dihybrid crosses. g) Describe the interaction between loci (epistasis) and predict phenotypic ratios in problems involving epistasis. (Knowledge of the expected ratio for various types of epistasis is not required; focus of this section is on problem solving). h) Explain how the environment may affect the phenotype (including how diet affects the diffe rentiation of honey bees and how temperature affects fur color of Himalayan rabbits). i) Explain the difference between genetic variation that is continuous (many, additive, genes control a characteristic) and discontinuous (one or few genes control a characteristic). j) Use the chi-squared test to test the significance of differences between observed and expected results.

Biology Unit, Tampines Meridian JC Page 4 of 75 LECTURE OUTLINE 1. Introduction 1.1 Definition of terms 1.2 Historical background 2. Mendelian Genetics 2.1 Monohybrid Inheritance and Mendel’s First Law – Law of Segregation 2.2 Dihybrid Inheritance and Mendel’s Second law – Law of Independent Assortment 2.3 Summary of Mendel’s Hypothesis 3. Interaction between Alleles of a Gene 3.1 Codominance 3.2 Incomplete dominance 3.3 Multiple alleles 4. Linkage 4.1 Autosomal linkage 4.1.1 Crossing Over 4.1.2 Genetic diagrams involving linked genes 4.2 Sex determination in humans and other organisms 4.3 Sex Linkage 4.3.1 Haemophilia 4.3.2 Red-green Colourblindness 4.3.3 Eye colour of Drosophila and Reciprocal Cross 5. Pedigree Chart 5.1 Background and Symbols used 5.2 Identifying Inheritance Patterns 6. Gene Interactions 6.1 Two-gene interaction can produce a 9:3:3:1 ratio 6.2 Epistasis produces modified 9:3:3:1 ratios 6.2.1 Coat colour in mice – 9:3:4 ratio 6.2.2 Plumage colour in chicken – 13:3 ratio 6.2.3 Colour of summer squash – 12:3:1 ratio 6.2.4 Flower colour in sweet peas – 9:7 ratio 6.2.5 Fruit shape of summer squash – 9:6