Genetics: Single-Gene Inheritance Patterns

Single-Gene Inheritance Patterns

• Single-gene inheritance refers to traits controlled by single genes.
• The "wild type" represents the most common form of a gene, organism, or cell, while "mutants" exhibit abnormal forms, differing from the wild type.
• Gene discovery begins by finding mutants with variations in a particular biological property.
• Crossing mutants with wild types and analyzing their offspring helps determine if the mutations follow single-gene inheritance patterns.
• If the offspring exhibit specific ratios of wild type to mutant characteristics, it suggests that the mutation is likely in a single gene and its function can be studied further.

The Chromosomal Basis of Single-Gene Inheritance Patterns

• Mendel's experiments with garden peas (Pisum sativum) laid the foundation for understanding single-gene inheritance.
• Mendel focused on seven phenotypic pairs, uncovering the rules of inheritance.
• He used pure lines, meaning offspring are identical due to inbreeding within the line.
• In crosses, he transferred pollen from one plant to another to control fertilization.
• Parental generation is denoted as "P," while subsequent generations are labeled "F," with F1 representing the first filial generation and F2 the second.
• Mendel's experiments led to the discovery of important ratios: 1:1, 3:1, 1:2:1.
• He established that inheritance is sex-independent, meaning it's not influenced by the organism's sex.

Mendel's First Genetic Cross

• Mendel crossed yellow-seeded plants with green-seeded plants, resulting in an F1 generation with 100% yellow seeds.
• This demonstrated that pea color is determined by a single gene with two forms: yellow and green.
• The dominance of the yellow phenotype over the green phenotype indicated that yellow is dominant and green is recessive.

Mendel's Second Genetic Cross

• Mendel self-pollinated the F1 generation, producing an F2 generation with a 3:1 ratio of yellow to green seeds.
• This further reinforced the concept of dominant and recessive alleles, illustrating how they segregate and recombine during inheritance.