These modified particles were thought to migrate via blood to the reproductive cells and subsequently could be inherited by the next generation. This was essentially a variation of Lamarck's incorrect idea of the "inheritance of acquired characteristics. Mendel picked common garden pea plants for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated. Pea plants have both male and female reproductive organs.
As a result, they can either self-pollinate themselves or cross-pollinate with another plant. In his experiments, Mendel was able to selectively cross-pollinate purebred plants with particular traits and observe the outcome over many generations. This was the basis for his conclusions about the nature of genetic inheritance. 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 ratio of yellow to green. This ratio occurs in later generations as well. Mendel realized that this underlying regularity was the key to understanding the basic mechanisms of inheritance.
He came to three important conclusions from these experimental results:. 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 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, these recessive traits re-appear in the next generation if these first-generation plants self-fertilise. Mendel hypothesised that parents contribute some particulate substance to the offspring which determine its heritable characteristics. We now know that these particles correspond to genes made of DNA.
Without any knowledge of the molecules involved, Mendel was able to infer that heritable particles are separated into gametes — eggs and sperm — and that offspring inherit one particle from each parent. Mendel was far ahead of his time, and his work was largely ignored for the next 35 years.
In he was appointed as an abbot and, overwhelmed with administrative duties, had little time left to continue his research. In , three scientists independently confirmed his work, but it was another 30 years before his conclusions were widely accepted. Learn more about Gregor Mendel's principles, alleles and inheritance on the Biology Online website.
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