YIJC [H2] CI2.12_Inheritance (N)(S)(vetted)

2025 JC2 BIOLOGY LECTURE NOTES CORE IDEA 2: GENETICS & INHERITANCE TOPIC 2.12: INHERITANCE Learning Outcomes (u) Explain the terms, locus, allele, dominant, recessive, codominant, incomplete dominance, homozygous, heterozygous, phenotype and genotype and linkage. (v) Explain how genes are inherited from one generation to the next via the germ cells or gametes. (w) Explain how genotype is linked to phenotype. (x) Use genetic diagrams to solve problems in dihybrid crosses , including those involving codominance, incomplete dominance, multiple alleles, sex linkage, autosomal linkage and epistasis. (y) Use genetic diagrams to solve problems involving test crosses. (z) 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. (aa) 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). (bb) Explain how the environment may affect the phenotype (including how diet affects the differentiation of honeybees and how temperature affects fur colour of Himalayan rabbits). (cc) Explain the difference between genetic variation that is continuous (many, additive genes control a characteristics) and genetic variation that is discontinuous (one or a few genes control a characteristics). (dd) Use the chi-squared test to test the significance between observed and expected results. Use the knowledge gained in this section in new situations or to solve related problems. Textbooks and References Campbell, Urry, Cain, Wasserman, Minorsky, Reece (2018) Biology – A Global Approach (11 th Edition)(Global Edition) Chapter 14: Mendelian Genetics pg. 319 – 340, Chapter 15: Linkage & Chromosomes pg. 344 - 361 (Pearson Publication) ISBN-10 1-292-17043-3 Note: This textbook is available in our library. You may wish to borrow them to supplement your reading when necessary. H2

2 Contents No. Sub-Topics 1 Introduction 2 Glossary of Terms 3 Genotype Influence on Phenotype 4 Inheritance of Gene from Parents 5 Mendel’s Experiment 6 Monohybrid inheritance 6.1 Mendel’s First Law: Law of Segregation 7 Dihybrid inheritance 7.1 Mendel’s Second Law: Law of Independent Assortment 8 Test Cross 9 Non-Mendelian Inheritance 9.1 Incomplete Dominance 9.2 Codominance 9.3 Multiple Alleles 9.4 Sex Linkage (includes Pedigree Analysis) 9.5 Autosomal Linkage 9.6 Epistasis 10 Environmental Influence on Phenotype 11 Variation 12 Chi-Squared (2) Statistical Test Summary Annex

3 1. Introduction • Different cells in a multicellular organism contains different number of sets of chromosomes inside the nucleus. Cells are either: o haploid - containing 1 set of chromosomes - e.g. gametes like sperm and o