Introduction to Genetics

Definition of Genetics

• The study of genes and how they are transmitted from parents to offspring (Heredity)
• Explains one's origin or ancestry, answering "How one becomes what he is like?"

Variations in Living Organisms

• Individuals of the same species may have common characteristics (Species characteristics) and individual differences (Individual characteristics)
• Variations provide the raw materials for adaptation

Types of Variations

Phenotype

• Various observable features by which we recognize the organism

Genotype

• Type of genes or hereditary material in the organism

Phenocopies

• Environmental alterations of phenotype, e.g. straightening of curly hair

Categories of Variations

Morphological or Structural

• Physical traits or gross anatomical features, e.g. shape of face, ears, eyes, hair color

Cellular, Subcellular, and Molecular

• Traits related to cell structure and function, e.g. kind of hemoglobin in RBC, glycoproteins on cell membrane

Physiological or Functional

• Biochemical and biophysical processes, e.g. ability to absorb glucose, distinguish colors, perform photosynthesis

Behavioral

• Combined structural and physiological traits, pattern of reactions to environment, e.g. IQ, mental retardation, tolerance level

Sexual

• Capacity for reproduction and associated features, e.g. primary sexual traits (differences in external genitalia and gonads), secondary sexual traits (non-sexual but related to mating and rearing of young)

Continuous and Discontinuous Variation

Continuous Variation

• Characteristic varies in small amounts between individuals, e.g. height, weight

Discontinuous Variation

• No intermediate forms, e.g. tongue-rolling, sex

Causes of Variation

• Genes (Inherited), e.g. sex determination, mental retardation, infant deformities
• [Other causes not mentioned in the text]