Gregor Mendel is famous today for his ground-breaking investigations and discoveries in the field of genetics. His pea plant experiments in the 19th century explained concepts such as dominant alleles and recessive alleles. Mendel concluded his experiments with two laws: the law of segregation and the law of independent assortment.
Heredity: The passing of characteristics from parents to offspring.
Genetics: The science of heredity.
Hybrid: The resulting offspring from a cross between two different types of parents.
Gene: Segment of DNA that codes for a single protein or RNA. Controls what characteristics are expressed.
Alleles: Variants of a specific gene.
Dominant Allele: The allele that is expressed as long as a dominant allele is present.
Recessive Allele: The allele that is expressed as long as no dominant alleles are present.
Law of Segregation: Mendel’s first law of inheritance. The law states that there are two factors controlling a given characteristic in which one dominates the other. These factors separate during reproduction and go to different gametes, or a mature reproductive cell that eventually unites with another gamete to reproduce.
Law of Independent Assortment: Mendel’s second law of inheritance. The factors controlling the different characteristics are inherited separately and therefore are not related.
Before Gregor Mendel’s discoveries, the blending inheritance was a widely popular theory to explain heredity.
To understand his observations, Mendel experimented with pea plants. The pea plants were good experimental subjects because they grow quickly, are easy to raise, and have several visible characteristics that exit in two different forms. For example, the flower color may be either white or purple. The seven characteristics that Mendel studied are shown in the diagram below.
In Mendel’s pea plant experiments, Mendel needed to control pollination, the fertilization step in the sexual reproduction of plants.
In his first set of experiments, Mendel experimented with just one characteristic (such as flower color) at a time
1. Mendel allowed each variety of pea plants to self-pollinate for several generations. He wanted to ensure that the offspring of each variety would display the same characteristics.
2. Mendel cross-pollinated two P generation plants with different characteristics.
3. The plants of the F₁ generation were allowed to self-pollinate.
P generation stands for parental generation. F generation stands for filial generation (filial means ”of a son or daughter”).
In his second set of experiments, Mendel experimented with two characteristics at a time, such as a yellow round seeds with green wrinkled seeds. He wanted to know if different characteristics are inherited together. For example, were yellow seeds always round and green seeds always wrinkled? The experimental steps were the same as the ones in the first set of experiments.
See biology study guide Mendelian Inheritance to learn how to predict an offspring’s characteristic.
Mendel's conclusions form the basis of modern genetics:
The law of segregation: When reproductive cells form, the pair of alleles separates, or segregates. Each reproductive cell, or gamete, receives one allele. During fertilization, two gametes combine, giving the offspring two alleles. The inherited alleles can be the same or different.
The law of independent assortment: The genes con-trolling different characteristics are inherited separately and therefore are not related.