Particulate inheritance theory
Encyclopedia
Particulate inheritance is a pattern of inheritance discovered by Mendelian theorists (or by Gregor Mendel
himself) showing that characteristics can be passed from generation to generation through "discrete particles" (now known as genes
). These particles can keep their ability to be expressed while not always appearing in a descending generation.
. They also did not understand how physical traits
are inherited from one generation to the next. Blending inheritance
was the common ideal at the time, but was later discredited by the experiments of Gregor Mendel. Mendel proposed the theory of particulate inheritance by using pea
plants (Pisum sativum) to explain how variation can be inherited and maintained over time.
). The terms "dominant" and "recessive" are used for the masking and the covered allele, respectively. All offspring from this cross are heterozygotes in terms of their genotypes. They also are tall (because the allele for tall masks the allele for short) in terms of their "phenotype
".
Gregor Mendel
Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
himself) showing that characteristics can be passed from generation to generation through "discrete particles" (now known as genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
). These particles can keep their ability to be expressed while not always appearing in a descending generation.
Scientific developments leading up to the theory
Early in the 19th century, scientists had already recognized that Earth has been inhabited by living creatures for a very long time. On the other hand, they did not understand what mechanisms actually drove biological diversityBiodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
. They also did not understand how physical traits
Trait (biology)
A trait is a distinct variant of a phenotypic character of an organism that may be inherited, environmentally determined or be a combination of the two...
are inherited from one generation to the next. Blending inheritance
Blending inheritance
Many biologists and other academics held to the idea of blending inheritance during the 19th century, prior to the discovery of genetics. Blending inheritance was merely a widespread hypothetical model, rather than a formalized scientific theory , in...
was the common ideal at the time, but was later discredited by the experiments of Gregor Mendel. Mendel proposed the theory of particulate inheritance by using pea
Pea
A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...
plants (Pisum sativum) to explain how variation can be inherited and maintained over time.
Blending Model vs. Particulate Model
- Blending Model:
- Offspring are a blend of both parents (i.e. in modern terms, alleles would blend together to form a completely new allele)
- The characteristics of the blended offspring are passed on to the next generation
- Variation is washed out over time
- Particulate Model:
- Offspring are a combination of both parents
- The characteristics of both parents are passed on to the next generation as separate entities
- Variation is maintained over time
Mendel's Laws
Since Mendel used experimental methods to devise his particulate inheritance theory, he developed three basic laws of inheritance: the Law of Segregation, the Law of Independent Assortment, and the Law of Dominance:Law of Segregation
Mendel's experiment with tall and short pea plants demonstrates how each individual plant has two particles called alleles. When a pea plant produces gametes (reproductive cells), it segregates one allele to each one.Law of Independent Assortment
The law states that when the parents differ from each other in two or more pairs of contrasting characters, the inheritance of one pair of character is independent to that of the other pair of character.Law of Dominance
In the pea plants, Mendel observed that the "T" allele (dominant) masked the effects of the "t" allele (recessiveRecessive
In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...
). The terms "dominant" and "recessive" are used for the masking and the covered allele, respectively. All offspring from this cross are heterozygotes in terms of their genotypes. They also are tall (because the allele for tall masks the allele for short) in terms of their "phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
".