[BIO] Chapter 18 - Inheritance

© Hee Xin Wei (Copyrighted) Topic 18: Inheritance

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 9.5% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested twice in section B in the past 5 years •may be an abstract topic •application questions

Inheritance Inheritance is the process by which genetic information is passed on from parent to child Hereditary traits that can be passed down to you by your parents: ability to roll tongue dimples right or left handed attached or free earlobe ability to taste PTC (bitter compound) allergy

variation Variations are differences in traits between individuals of the same species. Discontinuous variation Continuous variation Phenotype Few clear-cut phenotypes with no intermediate Range of phenotypes. Environment influence Rarely affected by environmental conditions Greatly affected by environmental conditions. Genes Controlled by one or few genes Controlled by many genes Additive effect Not present The effect of many genes add together and contribute the phenotype Graph Discrete groups Normal distribution Examples Blood groups, eyelid, flower colour in pea plant Height, skin colour, weight, intelligence © Hee Xin Wei (Copyrighted)

monohybrid hesitance codominance sex determination Key Concept © Hee Xin Wei (Copyrighted)

terms definitions Gene Gene is sequence of DNA nucleotides that stores information used to make a polypeptide, therefore gene is a unit of inheritance passed from parents to offspring Chromosome •Chromosome is a compact structure visible in the nucleus during cell division and it is made up of DNA •The place on the chromosome where the gene is located is called the gene locus. Allele •Alleles are different forms of a gene. •Alleles of a gene occupy the same locus on a pair of homologous chromosomes. •For example, eye colour gene has brown allele and blue allele Dominant A dominant allele is the allele that is always expressed in the phenotype, no matter under homozygous or heterozygous condition. Recessive A recessive allele is the allele that is only expressed under homozygous recessive condition. Codominant •When both alleles have an equal effect on the phenotype of the offspring. •Both alleles are expressed in the phenotype. Homozygous Organisms having two identical alleles of a particular gene. Allele can be either both dominant or both recessive. HeterozygousOrganisms having two different alleles of a particular gene. Phenotype •Phenotype refers to the expressed trait in an organism. •The phenotype of an organism is the result of its genes and the effects of its environment. Genotype •A genotype is the genetic makeup of an organism. •An organism’s genotype is homozygous for a trait if the two alleles controlling the trait are identical, heterozygous for a trait if the alleles controlling the trait are different. © Hee Xin Wei (Copyrighted)

Monohybrid Inheritance •The gene for flower colour of pea p