HOME

TheInfoList



OR:

Particulate inheritance is a pattern of inheritance discovered by
Mendelian genetics Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later populari ...
theorists, such as
William Bateson William Bateson (8 August 1861 – 8 February 1926) was an English biologist who was the first person to use the term genetics to describe the study of heredity, and the chief populariser of the ideas of Gregor Mendel following their rediscove ...
,
Ronald Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who ...
or
Gregor Mendel Gregor Johann Mendel, OSA (; cs, Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) was a biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (''Brno''), Margraviate of Moravia. Mendel was ...
himself, showing that
phenotypic trait A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two.Lawrence, Eleano ...
s can be passed from generation to generation through "discrete particles" known as
genes In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
, which 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 diversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity'') ...
. They also did not understand how physical traits are inherited from one generation to the next.
Blending inheritance Blending may refer to: * The process of mixing in process engineering * Mixing paints to achieve a greater range of colors * Blending (alcohol production), a technique to produce alcoholic beverages by mixing different brews * Blending (linguisti ...
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 The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
plants (''Pisum sativum'') to explain how variation can be inherited and maintained over time.


Blending model versus 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 methods


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 Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized ...
, the
Law of Independent Assortment Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later populariz ...
, and the
Law of Dominance Mendelian inheritance (also known as Mendelism) is a type of biology, biological Heredity, inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, an ...
:


Law of segregation

Mendel's experiment with tall and short pea plants demonstrates how each individual plant has two particles called
alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
. When a pea plant produces
gametes A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...
(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 characters is independent to that of the other pair of characters.


Law of dominance

In the pea plants, Mendel observed that the "T" allele ( dominant) masked the effects of the "t" allele (
recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
). The terms "dominant" and "recessive" are used for the masking and the covered allele, respectively. All offspring from this cross are
heterozygotes Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
in terms of their
genotypes The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
. They also are tall (because the allele for tall masks the allele for short) in terms of their "
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
".


Fisher

In a 1918 publication titled "The Supposition of Mendelian Inheritance Among Close Relatives,"
R.A. Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who ...
showed that particulate inheritance was capable of generating the vast amount of variation we see among closely related individuals. This helped to reconcile the Biometric and Mendelian schools of thought at the time, and was an important step in the
modern synthesis Modern synthesis or modern evolutionary synthesis refers to several perspectives on evolutionary biology, namely: * Modern synthesis (20th century), the term coined by Julian Huxley in 1942 to denote the synthesis between Mendelian genetics and s ...
.


Notes


References

* Campbell, N. E. & Reece, J. B. (2002). ''Biology'' (6th ed.). San Francisco: Benjamin Cummings. * "Particulate inheritance." ''BioEd Online''. Retrieved 3-5-2009 fro
BioEd Online Slides
{{DEFAULTSORT:Particulate Inheritance Classical genetics History of evolutionary biology