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MENDEL, THE FATHER OF THE MODERN GENETICS
Transcript of MENDEL, THE FATHER OF THE MODERN GENETICS
-First law or principle of uniformity: "When you cross two pure-bred individuals, the resulting hybrids are all equal." The crossing of two individuals homozygous dominant one (AA) and the other recessive (aa), originates only heterozygous individuals, ie individuals of the first filial generation are uniform among them (Aa).
Who was Mendel!?
Gregor Johann Mendel (July 20, 1822 – January 6, 1884)Austriar Empire, was a German-speaking Silesian, scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics.
His work was not appreciated when published in 1866. Hugo de Vries, Dutch botanist, Carl Correns and Erich von Tschermak separately rediscovered Mendel's laws in 1900.
Mendel was head of the Prelature of the Imperial and Royal Order Austrian Emperor Franz Joseph I, director emeritus of the Moravia Mortgage Bank, founder of the Austrian Meteorological Association, a member of the Royal and Imperial Moravian and Silesian Society for the Improvement of Agriculture , Science and knowledge of the country and gardener (learned from his father how to graft and grow fruit trees).
The error that the most of the people and Mendel committed is thinking that the uniformity of hybrids which Mendel observed in his experiments is to be a transmission law, because the domination doesn´t have anything in common with the transmission; it is joined with the genotype´s expression. That is why these Mendel´s observation doesn´t counts like a law. So transmission laws are only two: The segregation of independent characters (1st law) and the heritage of the independent characters (2nd law).
-Second law or the principle of segregation: "Certain individuals are able to transmit a character even if they don´t manifest it." The crossing of two individuals of the F1 (Aa) will origin a second filial generation in which reappears the phenotype "a", even all individuals from the F1 their phenotypes were "A". This makes it likely to Mendel that the character "a" had not disappeared, but it had only been overshadowed by the character "A" but at reproducing an individual, each character is secreted separately.
Third law or principle of independent combining: It refers to the polihybrid crossing (monohybrid: when considering only one character; polihybrid: when considering two or more characters). Mendel worked this crossing in peas, in which he observed characteristics (seed color and surface roughness) were on separate chromosomes. In this manner, noted that the characters are transmitted independently of each other. This law, however, stops being met when there is a link (two genes are very close and do not separate in meiosis).
Some scientists thinks that Mendel's first law is the beginning of segregation, the second the principle of uniformity and also they think that the third law isn´t considered a law.
Mendel's work was rejected at first in the scientific community, and was not widely accepted until after he died. During his own lifetime, most biologists held the idea that all characteristics were passed to the next generation through blending inheritance, in which the traits from each parent are averaged together. Instances of this phenomenon are now explained by the action of multiple genes with quantitative effects. Charles Darwin tried unsuccessfully to explain inheritance through a theory of pangenesis. It was not until the early 20th century that the importance of Mendel's ideas was realized.
Mendel's experimental results have later been the object of considerable dispute. Fisher analyzed the results of the F2 (second filial) ratio and found them to be implausibly close to the exact ratio of 3 to 1. Reproduction of his experiments has demonstrated the validity of his hypothesis, but the results have continued to be a mystery for many, though it is often cited as an example of confirmation bias. This might arise if he detected an approximate 3 to 1 ratio early in his experiments with a small sample size, and continued collecting more data until the results conformed more nearly to an exact ratio. It is sometimes suggested that he may have censored his results, and that his seven traits each occur on a separate chromosome pair, an extremely unlikely occurrence if they were chosen at random. In fact, the genes Mendel studied occurred in only four linkage groups, and only one gene pair (out of 21 possible) is close enough to show deviation from independent assortment; this is not a pair that Mendel studied. Some recent researchers have suggested that Fisher's criticisms of Mendel's work may have been exaggerated.