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 Principles OF Genetics part A By Prof.Dr/ Heba Taha Professor of Genetics Genetics Department Faculty of agriculture INTRODUCTION TO GENETICS  1. WHAT IS GENETICS  Genetics: The study of heredity.  Heredity is the relations between successive gener...

 Principles OF Genetics part A By Prof.Dr/ Heba Taha Professor of Genetics Genetics Department Faculty of agriculture INTRODUCTION TO GENETICS  1. WHAT IS GENETICS  Genetics: The study of heredity.  Heredity is the relations between successive generations.  Why do children look a little bit like their parents but also different?  What is responsible for these similarities and differences?  There are three main branches of modern genetics Molecular Biology or Molecular Genetics The study of heredity at the molecular level, and so is mainly concerned with the molecule DNA. It also includes genetic engineering and cloning Classical or Mendelian Genetics The study of heredity at the whole organisms level by looking at how characteristics are inherited. This method was pioneered by Gregor Mendel (1822-1884). Population Genetics which is the study of genetic differences within and between species, including how species evolve by natural selection. The word genotype refers to the alleles in an individual genotype may be indicated by letters ( DD; Dd ) or by short descriptive phrases (homozygous dominant , …..) The word Phenotype refers to the physical appearance of the individual 1- The principle of dominance In heterozygote , one allele may conceal the presence of another 2- The principle of segregation , In a heterozygote , two different alleles segregate from each other during the formation of gametes.  This principle is about genetic transmission , an allele is transmitted to the next generation even if it was present with a different allele in a heterozygote. (1:2:1) x (1:2:1) (3:1) x (3:1) Is Dominance Inclusive‫؟؟؟؟‬ Chemical Concept of Dominance ENZYME GENE effective enzyme Factor (A) non effective enzyme Factor (a)