20 July 2011 Gregor Mendel's 189 Birthday

WHO WAS GREGOR MENDEL?

Gregor Johann MENDEL was an Austrian monk and biologist whose work on heredity became the basis of the modern theory of genetics.
Mendel was born on July 22, 1822 in Heizendorf, Austria, (now known as Hyncice in Czechoslovakia). He was born Johann Mendel into a poor farming family. At that time it was difficult for poor families to obtain a good education and the young Mendel saw the only way to escape a life of poverty was to enter the monastery at Brunn in Moravis, (now Brno in Czechoslovakia). Here he was given the name Gregor. This monastery was the Augustinian Order of St Thomas, a teaching order with a reputation as a centre of learning and scientific enquiry.



MENDEL THE FAILURE
To enable him to further his education, the abbot arranged for Mendel to attend the University of Vienna to get a teaching diploma. However, Mendel did not perform well. He was nervous and the University did not consider him a clever student. Mendel's examiner failed him with the comments, " he lacks insight and the requisite clarity of knowledge". This must have been devastating to the young Mendel. who in 1853 had to return to the monastery as a failure. As this was a teaching order, Mendel had to decide whether to stay on at the monastery as a failed teacher - or return to what?

WHAT TO DO NEXT?

While studying in Vienna, Mendel had been impressed by the work of a biologist called Frank Unger whose practical view of inheritance, free from spiritual influences, seemed to reflect his own farming background. This gave Mendel the idea to stay on at the monastery and use his time to carry out practical experiments in biology. He must have had to approach the abbot very carefully to ask to be allowed to do this, as the bishop refused to allow the monks to even teach biology.




After about two years Mendel began his investigation into variation, heredity and evolution in plants. He chose to study in detail the common garden pea, Pisum, which he grew in the monastery garden.


Between 1856 and 1863 Mendel patiently cultivated and tested at least 28 000 pea plants, carefully analysing seven pairs of seeds for comparison, such as shape of seed, colour of seed, tall stemmed and short stemmed and tall plants and short plants. Mendel worked on this for several years, carefully self-pollinating and wrapping each individual plant to prevent accidental pollination by insects. He collected the seeds produced by the plants and studied the offspring of these seeds observing that some plants bred true and others not. Mendel discovered that by crossing tall and short parent plants he got hybrid offspring that resembled the tall parent rather than being a medium height blend. He explained this conceived the concept of heredity units, now called genes. These often expressed dominant or recessive characteristics. He then worked out the pattern of inheritance of various traits and produced two generalisations that became known as the laws of heredity. Mendel's observations led him to coin two terms which are still used in present-day genetics:
* dominance for a trait that shows up in an offspring
* recessiveness for a trait masked by a dominant gene.


source : http://www.zephyrus.co.uk/gregormendel.html

Rise of Evolution

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Gregor Mendel

1865

Gregor Mendel uses peapods and discovers that traits are passed down through generations, genes. At the time of his discoveries no one pays him any attention. There are scientific studies of genes now.

(I don't understand a thing, but it looks cool, so I reprint samples of his stuff HERE:)

In cross-pollinating plants that either produce yellow or green pea seeds exclusively, Mendel found that the first offspring generation (f1) always has yellow seeds. However, the following generation (f2) consistently has a 3:1 ratio of yellow to green. This 3:1 ratio occurs in later generations as well. Mendel realized that this was the key to understanding the basic mechanisms of inheritance. Reproductive structures of flowers He came to three important conclusions from these experimental results: 1. that the inheritance of each trait is determined by "units" or "factors" that are passed on to descendents unchanged (these units are now called genes ) 2. that an individual inherits one such unit from each parent for each trait 3. that a trait may not show up in an individual but can still be passed on to the next generation. It is important to realize that, in this experiment, the starting parent plants were homozygous for pea seed color. That is to say, they each had two identical forms (or alleles ) of the gene for this trait--2 yellows or 2 greens. The plants in the f1 generation were all heterozygous . In other words, they each had inherited two different alleles--one from each parent plant. It becomes clearer when we look at the actual genetic makeup, or genotype , of the pea plants instead of only the phenotype , or observable physical characteristics. Note that each of the f1 generation plants (shown above) inherited a Y allele from one parent and a G allele from the other. When the f1 plants breed, each has an equal chance of passing on either Y or G alleles to each offspring. With all of the seven pea plant traits that Mendel examined, one form appeared dominant over the other, which is to say it masked the presence of the other allele. For example, when the genotype for pea seed color is YG (heterozygous), the phenotype is yellow. However, the dominant yellow allele does not alter the recessive green one in any way. Both alleles can be passed on to the next generation unchanged. Mendel's observations from these experiments can be summarized in two principles: 1. the principle of segregation 2. the principle of independent assortment According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance. We now know that this segregation of alleles occurs during the process of sex cell formation (i.e., meiosis ). Segregation of alleles in the production of sex cells VI.  The Rules of Probability Sometimes, it is easier to use the product rule than Punnett Squares to determine the results of a cross. This is especially true when more than two traits are being followed in the cross or when the relative frequency of a particular genotype or phenotype is being sought. The use of this rule is possible because of Mendel’s Law of Independent Assortment – that is, the segregation of the factors for each trait in a cross is an independent event from the segregation of the factors of all other traits in the cross. Consider the following example: A cross is made between the two plants with the genotypes (Aa, Yy, rr) and (Aa, Yy, Rr), where A = purple flowers, a = white flowers; Y = yellow seeds, y = green seeds; and R = round seeds and r = wrinkled seeds. What fraction of the offspring would you expect to have the genotype (Aa,yy,rr) ? To use the product rule to answer this question, you would first analyze each trait separately. Then you would simply multiply the individual probabilities together to arrive at a final answer. ½  x  ¼   x  ½   =  1/16            A/a  x  A/a                                       ½  A/a          Y/y  x  Y/y                                        ¼ y/y        r/r  x  R/r                                         ½ r/r The product rule can also be used to predict the phenotypes of the offspring of a genetic cross. For example, using the same cross as above, what fraction of the offspring would you expect to have purple flowers and yellow, wrinkled seeds? The easiest way to solve this type of problem is to express the phenotype as a genotype and then proceed as in part a. purple flowers  =  A__ yellow seeds =  Y__ wrinkled seeds = rr Aa  x  Aa                                 ¾ A__ ¾  x  ¾   x  ½   =  9/32              Yy  x  Yy                                  ¾ Y__        rr  x  Rr                                  ½ rr

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