RVHS 16. Inheritance 9477

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 1 River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance Name: ( ) Class: 25J___ Date: References Title Authors Biology (8th Edition) Campbell and Reece Biological Science 1 and 2 (3rd Edition) Green, Stout and Taylor Principles of Genetics Gardner, Simmons, Snustad An Introduction to Genetic Analysis (7th Edition) Griffiths, Miller, Suzuki, Lewontin and Gelbart Websites URL Description https://knowgenetics.org/mendelian-genetics/ Mendelian Genetics http://www.dnaftb.org/dnaftb/1/concept/ Animation on Mendel’s experiment H2 Biology Syllabus 9477 (2025) Candidates should be able to use the knowledge gained in the following section(s) in new situations or to solve related problems. Related Topics Content The Cell Cycle The Structure of Nucleic Acids and Gene Expression • Replication and division of nuclei and cells • Understanding of chromosome number and variation • Effect of meiosis on chromosome number and variation • Central Dogma - DNA to RNA, RNA to protein Learning Outcomes 2F. Inheritance a. Explain the terms: locus, allele, dominant, recessive, codominant, 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, multiple alleles, sex linkage, 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, using examples including the effect of diet on differentiation of honeybees. i. Explain the difference between genetic variation that is continuous (many, additive genes control a characteristic) and genetic variation that is discontinuous (one or a few genes control a characteristic).

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 2 j. Use the chi -squared test to test the significance of differences between observed and expected results. Lecture Outline I. Introduction A. Terminology B. Inheriting genes in sexual reproduction C. How genotype is linked to phenotype? D. Mendel’s experiment II. Monohybrid Crosses and Principle of Segregation A. Representing monohybrid cross in symbols B. Explanation of monohybrid cross in term of probability C. Testcross D. Monohybrid inheritance in humans III. Extending Mendelian genetics A. Co-dominance B. Multiple alleles C. Lethal genes IV. Sex Determination A. Sex linkage B. Reciprocal cross C. Human pedigree V. Dihybrid Crosses and Principle of Independent Assortment A. Representing dihybrid cross in symbols B. Explanation of dihybrid cross in term of probability C. Testcross VI. Linkage A. Morgan’s Drosophila experiment B. Types of linkage C. Gene mapping and crossover values VII. Gene Interaction A. Gene interaction producing new phenotype B. Epistasis B1. Dominant epistasis B2. Recessive epistasis B3. Duplicate recessive VIII. Variation A. Continuous variation B. Discontinuous variation C. Influence of environment D. Sources of variation IX. Statistical Tests

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 3 I. Introduction • Genetics is the study of inheritance of characteristics by offspring from their parents. • In the study of genetics, subtle but recognizable differences exist between individuals of the same species (even between parents and offspring) which geneticists term as variation. A. Terminology Gene • A basic hereditary unit located on a specific locus of a chromosome. • A segment of DNA with unique nucleotide (base) sequence coding for a particular RNA molecule / polypeptide chain. • An unit of inheritance determining a specific phenotype of an individual. Locus • position of a gene/allele on a chromosome or within a DNA molecule Allele • alternative form of the same gene and responsible for determining the contrasting characteristics of a gene. • For instance, there is a gene responsible for the stem height of pea plant; however, there are 2 forms of it:  allele for tall stem  allele for short stem • Each allele has a unique nucleotide sequence, which may result in different phenotypes.  Alleles are found to be identical in most of their sequences and differ only at one or a few nucleotides of the thousands of nucleotides that make up the gene.  The following diagram represents the DNA of two alleles of one gene and their difference in the nucleotide sequence. Allele 1 Allele 2 • Alleles occupy the same locus of a pair of homologous chromosomes. Fig. 1 Alleles, alternative versions of a gene. Source: Biology (8th Edition) pp. 265 Allele for tall stem Locus for height gene Homologous pair of chromosomes Allele for short stem ATTGG AACCG

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 4 Dominant allele • The allele which influences the appearance of the phenotype even in the presence of an alternative allele, i.e. in homozygous or heterozygous condition • encodes a functional protein • represented by a capital letter in a genetic cross. E.g TT or Tt Recessive allele • The allele which influences the appearance of the phenotype only in the presence of another identical recessive allele, i.e. in the homozygous condition • Encodes for a non-functional protein or lack of protein • represented by a lower-case letter in a genetic cross. E.g. Tt or tt Homozygous • When both alleles at a given locus are identical in diploid condition, may be either homozygous dominant (E.g. TT) or homozygous recessive (E.g. tt). • Homozygous organisms are referred to as homozygotes. • Homozygous individual breeds true (true breeding/pure breeding) i.e., consistently produce the same characteristic when the plants were self-fertilised because its entire offspring receive the same allele from this parent. Heterozygous • When different alleles are present in diploid condition. • Dominant form of the allele is expressed, masking the presence of the recessive allele. • Heterozygous organisms are referred to as heterozygotes. They do not breed true. Molecular nature of alleles  In the heterozygote, the protein produced by the functional allele is enough for the normal needs of the cell; so the functional allele acts as a dominant allele. Co- dominance • Both alleles are equally expressed in the phenotype of the heterozygote. Genotype • genetic makeup or genetic constituents. (Fig. 2) Phenotype • observable characteristics that are the expression of its genotype. (Fig. 2) * Character - a heritable feature, such as flower colour, that varies among individuals. * Trait - each variant for a character, such as purple or white colour for flowers

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 5 There are actually two categories of purple-flowered plants: PP (homozygous) and Pp (heterozygous). Fig. 2 Phenotype vs genotype Fig. 3 Summary of terms used in Genetics B. Inheriting genes in sexual reproduction

River Valley High School 2025 JC1 H2 Biology Lecture Topic 16: Inheritance 6 • In sexual reproduction, haploid gametes are formed, by meio