GENETICS 1

1 EJC H2 Biology T4W1 Genetic Basis for Variation I Genetics & Inheritance – Genetic Basis for Variation I 1. Introduction Organisms inherit genetic information from their parents. To appreciate how characteristics or conditions are passed on in a family, it is important to understand the basic laws of inheritance. Gregor Mendel was the first person to describe the manner in which traits are passed on from one generation to the next. By experimenting with pea plant breeding, Mendel developed the principles of inheritance that described the transmission of genetic traits, before anyone knew genes exi sted. However, not all orga nisms pass their genes on the same way as the pea plant and therefore Mendel’s principles of inheritance only explain the most basic phenomena of inheritance. Other than Mendelian inheritance, you will also learn of non-Mendelian inheritance (e.g. autosoma l linkage, epistasis), as well as how the environment plays a role in determining the phenotype of an organism. Statistical tests, such as the chi -squared test, which allow us to test the significance of differences between observed an expected results of genetic crosses will also be covered. 2. Learning Outcomes u. Explain the terms: locus, allele, dominant, recessive, codominant, incomplete dominance, homozygous, heterozygous, phenotype, genotype and linkage. v. Explain how ge nes 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, autos omal 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 rations from dihybrid crosses. bb. Explain how the environment may affect the phenotype (including how the diet affects the differentiation of honey bees and how temperature affects fur colour of Himalayan rabbits). 3. References Campbell, N.A. and Reece, J.B. (2008). Biology, 9th edition. Pearson.

2 EJC H2 Biology T4W1 Genetic Basis for Variation I Contents 1. Introduction ............................................................................................................... 1 2. Learning Outcomes.................................................................................................... 1 3. References ................................................................................................................. 1 4. Common Terms to Understand ................................................................................. 3 5. Labelling Conventions for Alleles .............................................................................. 6 6. From Genotype To Phenotype .................................