Fundamental Genetics Terms and Definitions

Fundamental Genetics Terms and Definitions

Genetics

Genetics: The science that studies heredity and the transmission of characters resulting from the segregation of chromosomes.

Phenotype

Phenotype: All observable traits or characteristics of an individual. The phenotype has a close relationship with the environment in which the individual develops.

Genotype

Genotype: Represents the genetic information an individual has inherited from their parents.

Homozygote

Homozygote: An individual with a pair of identical alleles for a character (for example, AA or aa).

Heterozygote

Heterozygote: An individual with a pair of different alleles for a character (symbolized Aa). The heterozygote often manifests the dominant trait.

Zygote

Zygote: The fertilized egg formed by the fusion of a female and a male gamete.

Gene

Gene: A stretch of DNA that, when expressed, confers a particular feature or trait to a living organism.

Gametes

Gametes: Sex cells that merge during fertilization to form a new individual.

Codominance and Intermediate Forms

Codominance: Occurs when neither allele completely dominates the other. In codominance both alleles are expressed. Related concepts include complete dominance and incomplete (intermediate) dominance, where the heterozygote shows an intermediate phenotype.

Crossing

Crossing: The mixing of genes between different varieties, strains, breeds, or, in some contexts, species.

Dihybrid Cross

Dihybrid cross: A cross that considers the inheritance and behavior of two different pairs of genes.

Subsidiary Generations

Subsidiary generations:

• F1 (First filial generation): The set of descendants resulting directly from a cross (for example, of seeds or animals).
• F2 (Second filial generation): The descendants produced from crosses among individuals of the first generation.

Mendel's Laws

Mendel's First Law (Uniformity): When two pure strains differing in a character are crossed, all descendants of the first filial generation are hybrids and are uniform for that character.

Mendel's Second Law (Segregation/Independent Factors): Each character is controlled by two factors (now called alleles) that segregate independently during the formation of gametes.

Chromosome

Chromosome: One of the small, typically rod-shaped bodies in the cell nucleus that organize chromatin; chromosomes are visible during mitosis and meiosis.

Inheritance

Inheritance: The transmission of genetic material and traits (anatomical, physiological, etc.) through the cell nucleus from parents to offspring.

Allele

Allele: Each alternative form of a gene that differs in sequence and can produce specific modifications in the gene's function.

Dominant Trait

Dominant trait: A feature that appears in the first generation when a dominant allele is present.

Recessive Trait

Recessive trait: A characteristic that typically appears in later generations (for example the second generation) when two recessive alleles are combined.

Monohybrid Cross

Monohybrid cross: A cross that analyzes the inheritance of a single gene. Example: hair color.

Disjunction of Gametes

Disjunction of gametes: The separation of chromosomes during gamete formation, which results in a reduction of chromosome number in the gametes.

Complete Dominance

Complete dominance: The case when one allele in the heterozygote expresses its effect fully, producing the same phenotype as in the homozygote. The dominant allele determines the protein structure that defines the character whether it is present in one (heterozygous) or two copies (homozygous).