Mendel's principles of genetics
From Conservapedia
Gregor Mendel was an Augustinian Monk who taught natural history. In an effort to test Lamarck's theory that the environment and physical experience produce the traits an offspring inherits, he crossbred and observed successive generations of sweetpeas and mice, and his conclusions are his principles of genetics.
He transferred pollen from one variety of pea to another which was the same in all but one characteristic. For example, he crossed tall pea plants with white flowers and a wrinkled pea with short pea plants with white flowers and a wrinkled pea. The first generation of offspring were called F1 hybrids. He used their own pollen to self-pollinate the F1 hybrids to produce the F2 generation, and self-pollinated F2s to produce the F3 generation and so on.
In this experiment, the F1 plants were all tall. Mendel called this the dominant form. He called the short form recessive, because it seemed to disappear. But in the F2 generation, short peas reappeared. When Mendel counted them, he found there were always three tall peas to every short pea. When he pollinated the F2 generation he found that the short peas produced short peas, and one of the tall peas produced tall peas, but the other two tall peas repeated the pattern of three tall and one short. [1] Thus producing the ratio of 3 dominant phenotypes to 1 recessive phenotypes (in hybrid crosses).
Later scientists showed this law of three dominants to one recessive applied to other species. For example, in humans brown eyes are dominant over blue. If a brown eyed boy married a blue-eyed girl, the children would probably all have brown eyes. But if one of those brown-eyed children married a blue-eyed partner and had four children, one of those children would probably have blue eyes.
Scientists of the time largely ignored Mendel's work in spite of the fact that he reported on the results of his observations at the meetings of the Association for Natural Research in Brünn on the evenings of February 8th and March 8th, 1865. The Association published the written accounts of these observations in 1866, under the title Versuche über Pflanzen-Hybride. He discontinued his scientific studies of inheritance when he was elected Abbot of the Augustinian monastery in Brünn, Cyrill Franz Napp in 1868.[2]
Updated terminology:
- The traits of an organism are determined by its genes
- Each organism has two alleles that make up the genotype of a given trait
- In sexual reproduction, each parent contributes ONLY ONE of its alleles to the offspring
The way a genotype is expressed in an organism is called its phenotype. For many traits the phenotype results from the interaction between the genotype and the organism's environment.
For specific traits, an allele can be dominant or recessive. A dominant allele is expressed in the phenotype regardless of the other allele. A recessive allele is only expressed when both alleles are recessive. If one allele is not completely dominant, the phenotype can show a combination of the phenotype of each allele. Some traits are determined by a combination of several genes, and therefore the phenotype is determined by a combination of all the relevant alleles.[3]
Exceptions
Some types of genes do not have the assumed one gene, two allele system in Mendelian genetics. Examples can include human skin color or human color blindness (which is a sex-linked gene). Also Mendelian genetics assumes that none of the genes cross over to form different genotypes.
