Mendel’s 3 laws and peas: this is what they teach us

It has long been known that inside cells is DNA, which contains all the information necessary for the proper development and functioning of an organism. In addition, it is a hereditary material, which means that it is transferred from parents to sons and daughters. What can now be explained some time ago had no answer.

Throughout history, different theories have emerged, some more precise than others, trying to find logical answers to natural events. In that case, Why does the son have part of the features of the mother but also part of the father? Or why does a child have a characteristic of his grandparents? The mystery of inheritance has had its significance for ranchers and farmers seeking more productive offspring from animals and plants.

The surprising thing is that these doubts were resolved by a priest, Gregor Mendel, who stipulated Mendel’s laws and that he is currently recognized as the father of genetics. In this article, we will see what this theory consists of which, together with the contributions of Charles Darwin, laid the foundations of biology as we know it.

    Discover the basics of genetics

    This Austro-Hungarian priest during his life at the Brno convent, became interested in peas after seeing a possible pattern in his offspring. This is how he began to have different experiences, Which consisted of crossing different types of peas and observing the result in their offspring.

    In 1865 he presented his work to the Brno Natural History Society, but they quickly rejected his proposal, so his findings were not published. It took thirty years for these experiences to be recognized and for Mendel’s current laws to be established.

      Mendel’s 3 laws

      The father of genetics, through his work, came to the conclusion that they exist three laws to explain how genetic inheritance works. In some bibliographies, there are two, the first two being joined by a third. However, keep in mind that many of the terms I will be using here were unknown to Mendel, such as genes, variants of the same gene (allele), or genetic dominance.

      To try to make the explanation more pleasant, the genes and their alleles will be represented by letters (A / C). And remember, the offspring receive one allele from each parent.

      1. Principle of uniformity

      To explain this first law, Mendel made crosses between peas yellow (AA) with another rarer species of green peas (aa). The result is that in the offspring, the yellow color (Aa) dominates, without the presence of green peas.

      The explanation for what happened in this first Mendel’s law, according to this researcher, is that the yellow allele dominates the green alleleYou only need one of the two alleles in a life form to be yellow in order to express itself. It should be added that it is essential that the parents are purebred, that is to say that their genetics are homogeneous (AA or aa) for this to happen. Therefore, their offspring become 100% heterozygous (Aa).

      2. Principle of segregation

      Mendel continued to cross species of peas, this time the results of his previous experiment, namely heterozygous yellow peas (Aa). The result was surprising, since 25% of the offspring were green, even though their parents were yellow.

      In this second Mendel’s law, we explain that if the parents are heterozygous for a gene (Aa), its distribution in the offspring will be 50% homozygous (AA and aa) and the other half heterozygous (Aa). This principle explains how a child can have green eyes like his grandmother, if his parents have brown eyes.

      3. Principle of independent character separation

      This last law of Mendel is a little more complex. To arrive at this conclusion, Mendel crossed species of smooth yellow peas (AA BB) with other raw green peas (aa bb). When the above principles are met, the resulting offspring are heterozygous (Aa Bb), which crossed them.

      The result of two smooth yellow peas (Aa Bb) was 9 smooth yellow peas (A_ B_), 3 smooth green peas (aa B_), 3 rough yellow peas (A_ bb), and 1 rough green pea (aa bb).

      This third law of Mendel, what she tries to demonstrate is that features are distributed independently and do not interfere with each other.

      Mendelian heritage

      It is true that with these three laws, Mendel can explain a large part of the cases of genetic inheritance, but he manages to grasp all the complexity of the inheritance mechanisms. There are many types of inheritances that do not follow these guidelines, called non-Mendelian inheritances. For example, sex-related inheritance, which depends on the X and Y chromosomes; or multiple alleles, that the expression of one gene depends on other genes cannot be explained by Mendel’s laws.

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