Chapter 5

• Genetics: the study of heredity and its variation
• Gene: basic unit of heredity; each gene occupies a certain location on a chromosome
• Alleles: two or more alternate forms of a gene
• Dominant Alleles: alleles of this type determine the expression of the genetic trait in the offspring
• Recessive Alleles: alleles of this type are overruled by dominant alleles, which determine the genetic trait.
• Character: genetic term for a heritable feature (i.e eye colour)
• Trait: genetic term for each variant for a particular character (i.e blue or brown eye)
• Monohybrid cross: a cross that involves only one allele pair of contrasting traits
• True breeding: upon self-pollination all offspring are of the same variety
• Hybridization: mating (crossing) of different variety of plants
• F1 (generation): hybrids resulting from a cross between two true breeding parents
• F2 (generation): offspring resulting from self-pollination of F1 hybrids
• Blending Hypothesis (1800s): genetic material contributed by both parents
• If true, would result in uniformity of traits or in other words, the original characteristics of the parents would not appear in future generations
• Particulate Model (Genes): parents pass on discreet heritable units (genes) that retain their separate identities in offspring.
• Genes get passed from generation to generation in undiluted form.
• Phenotypic ratio of dihybrid cross is 9:3:3:1.
• For traits exhibiting dominant gene action, two affected individuals can have an unaffected child.
• The phenotype generally appears every generation for traits exhibiting dominant gene action.
• Two unaffected parents only have unaffected offspring for traits exhibiting dominant gene action.
• For traits exhibiting recessive gene action, two unaffected parents can have affected offspring.
• Two affected parents cannot have an unaffected offspring for traits exhibiting recessive gene action.