Introduction to Genetics

Genetics: The study of heredity (inheritance) and variation.

Some inheritable characteristics include

• Size
• Height/length
• Colour/type
• Shape
• Yield

Terminology

Heredity is the transmission of traits from parents to offspring

Trait is a character of the organism; e.g. height

Gene is a single pair of hereditary factors.

Alleles (gene pairs) are alternative forms of genes controlling a particular characteristic.

Chromosomes; threadlike structures found in nuclei of living organisms that carry genes, which are hereditary materials

Deoxyribonucleic Acid (DNA) is a nucleic acid molecule in the form of a twisted double helix strand that is the major component of chromosomes and carries genetic information.

Inherited characteristics are traits that are passed down to offspring during sexual reproduction

Acquired characteristics are traits that are as a result of adaptations due to the environment and are not inherited

Genotype is the genetic constitution of an organism.

Phenotype is the outward appearance or an organism.

Dominant gene is a character expressed in the phenotype when homozygous or heterozygous

Recessive gene is a character only expressed in homozygous state

Homozygous: when the allelic genes are identical e.g. TT, tt

Heterozygous: when the allelic genes are different at a particular locus e.g. Tt

F1: first filial generation i.e. the first generation produced when two varieties can be crossed

F2: second filial generation i.e. product of offspring or from F1 generation

Monohybrid inheritance involves the transmission of just one pair of contrasting characteristics (traits).

Complete dominance refers to where only one dominant character is expressed while the other character, which is recessive, is not expressed in the heterozygous state.

Incomplete dominance: no allele completely dominates the other i.e. all alleles express themselves equally.

Test cross is a cross between individual of unknown genotype with a homozygous recessive individual

Back cross is a test cross where an offspring is crossed with one of its parents.

Multiple alleles is a set of more than two alleles that may determine a character; e.g., ABO Blood group system.