Mendel's pea experiments revolutionized our understanding of genetic inheritance. By carefully selecting plants and controlling pollination, he uncovered patterns in trait inheritance. His work laid the foundation for modern genetics, revealing how dominant and recessive alleles shape offspring characteristics.

Mendel's findings explain why some traits skip generations or appear unexpectedly. His discoveries about monohybrid crosses and trait variation continue to influence our understanding of genetics today, from predicting eye color to understanding complex genetic disorders.

Mendel's Experiments and Genetic Inheritance

Effectiveness of Mendel's pea experiments

• Mendel selected pea plants for his experiments because they possess several easily observable and distinct characteristics (flower color, seed shape) and reproduce quickly, allowing for multiple generations to be studied in a short time
• Controlled pollination by removing the male parts of the flower (anthers) and manually transferring pollen from another plant, ensuring that the offspring resulted from the desired cross
• Carefully observed and recorded the numbers of each trait (inheritance) in the offspring, enabling him to identify patterns of inheritance
• Tracked the inheritance of single traits (monohybrid crosses) through multiple generations, revealing the behavior of dominant and recessive alleles
• Used large sample sizes in his experiments, which allowed him to observe clear ratios in the offspring and draw reliable conclusions
• Applied mathematical principles to analyze the results and derive general principles of inheritance, such as the Law of Segregation and the Law of Independent Assortment

Outcomes of monohybrid crosses

• Alleles are alternative versions of a gene that control a specific trait (purple or white flower color)
• Dominant alleles ($A$) mask the expression of recessive alleles when present, while recessive alleles ($a$) are only expressed when no dominant allele is present
• In a monohybrid cross, organisms that are true-breeding for contrasting traits (AA x aa) are crossed to study the inheritance of a single characteristic
• Punnett squares, a graphical tool, can be used to predict the genotypic and phenotypic ratios of the offspring based on the parental genotypes
• The genotypic ratio for a monohybrid cross between two heterozygous individuals (Aa x Aa) is 1:2:1 (1 AA : 2 Aa : 1 aa)
• The phenotypic ratio for a monohybrid cross between two heterozygous individuals is 3:1 (3 dominant : 1 recessive), as the dominant trait is expressed in both homozygous dominant (AA) and heterozygous (Aa) individuals

Continuous vs discontinuous variation

• Variation refers to the differences in characteristics among individuals within a population, which can be either discontinuous or continuous
• Discontinuous variation involves traits that have distinct categories with no intermediate forms
  • Flower color (purple or white) and seed shape (round or wrinkled) in Mendel's pea plants exhibit discontinuous variation
  • Often controlled by a single gene with dominant and recessive alleles, resulting in clear-cut differences between phenotypes
• Continuous variation involves traits that have a range of values with intermediate forms, often following a normal distribution
  • Height, weight, and skin color in humans are examples of traits that display continuous variation
  • Typically controlled by multiple genes (polygenic traits), each with a small effect on the trait, leading to a gradual range of phenotypes
  • Environmental factors (diet, climate) can also influence the expression of continuous traits, contributing to the observed variation within a population

Fundamentals of Genetics

• Heredity is the passing of traits from parents to offspring
• Genetics is the scientific study of heredity and how traits are passed down through generations
• A trait is a specific characteristic of an organism, such as flower color or seed shape
• Genes are segments of DNA that code for specific traits and are located on chromosomes
• Chromosomes are structures in the cell nucleus that carry genetic information
• Meiosis is the process of cell division that produces gametes with half the number of chromosomes, crucial for sexual reproduction and genetic diversity