What Is Mendel's First Law?

Mendel's First Law consists of The principle of dominance. This principle indicates that a hybrid generation (F1) of heterocygotic hybrids and homogenous physical characteristics must result from a cross between two individuals with pure genetic characteristics (parental generation P).

The result of the mixture of parents in generation P is explained by the dominance of certain genetic characteristics or alleles over others. Mendel managed to explain this principle by crossing plants of the generation P and resulting in plants of homogeneous appearance, equal to one of the individuals of the parental generation.

Mendel's First Law

The law of dominance indicates that the physical characteristics or alleles of the parents have equal probabilities of being transmitted to the children, however, among these alleles there are some that are dominant and another recessive. Dominators will be the ones most likely to appear in the next generations.

Gregor Mendel was an Austrian botanical monk who dedicated much of his life to the study of what would later become the modern laws of genetics. The results of their experiments were based on the observation of the results between crosses of pure and hybrid traits of peas.

During his time in the monastery, Mendel crossed more than 5,000 specimens of pea plants with the aim of developing individuals of pure characteristics, who would later act as a P.

In 1886 he established the three laws of genetics that would be retaken during the twentieth century by schoolchildren and geneticists (Starr, Evers, & Starr, 2011).

Once the laws of Mendel were retaken, instruments were developed such as the Punnett chart, a table where the alleles of diploid organisms can be mixed in order to determine the probabilities of an individual of the F1 or F2 generation inheriting the Characteristics of one of their parents.

Mendel Crosses and Experiments

Mendel crossed and experimented with approximately 5,000 pea plants until individuals with pure characteristics were obtained. These individuals were later used by him as the parental (P) generation to make crosses between pure individuals and to establish the first principles of generic inheritance, now known as Mendel's Laws (Mendel & Corcos, 1966).

Mendel's first law is the Law of Dominance, the second is the Law of Segregation and the third is the Law of Independent Association. These laws laid the groundwork for later genetic studies and were only taken into account during the 20th century (Hasan, 2005).

While Mendel performed the crosses of the pea plants, he began to notice certain interesting patterns.

When he crossed pure individuals with long stem, with pure individuals with short stem, he expected to obtain individuals with a medium stem length, however, all the resulting pea plants in the F1 generation had the long stem.

These results were also evident in crosses where the visible characteristics were the color or the roughness of the seeds of the plants. In this way, a population or first generation subsidiary (F1) of equal appearance to one of the parents was always obtained as a result.

Mendel noted that when parents or individuals of the P generation had opposing characteristics (high and low, smooth and rugged, green and pink), the phenotype or physical appearance of their offspring would resemble only one parent.

In this way, Mendel could identify that there was a factor that made the pea plants one of the characteristics opposite to the other and that when mixing these characteristics there was one that was dominant over the other. (Bortz, 2014)

Law of Dominance

In diploid organisms, that is, they have two sets of chromosomes, there are two characteristics that could be inherited by the children, known as alleles. During the fertilization process, maternal and paternal sexual cells or gametes unite, coupling alleles from both parents.

When parental alleles are different, they are said to be heterozygotes and one of them will determine the dominant physical characteristic of the next generation (Bailey, 2017).

What Is Mendel's First Law?

Set of human diploid chromosomes

The dominant allele will always be visible and will mask the other allele that will be called recessive. The dominant alleles are always represented by capital letters, while the recessive alleles are represented by lower case letters in the Punnett box.

Punnett picture

At the beginning of the 20th century, Mendel's laws began to be studied as the basis of modern genetic theory. It was then that the English geneticist Reginald Punnett was able to graph what Mendel had explained more than forty years ago in a table that is known today as Punnett Table.

The Punnett Chart allows you to understand the probabilities of inheriting certain genetic characteristics.

This chart serves for animal or plant breeders to develop individuals with certain desirable physical characteristics. It can also help people determine patterns of genetic inheritance within their families (Study.com, 2015).

As we said earlier, the law of dominance is determined by the presence of heterozygous alleles where one of them is dominant over the other. The dominant allele is represented with a capital letter, in this case T and the recessive with a lowercase letter, in this case t.

In the case where the parent generation or parent generation is pure, the alleles will be manifested as TT and tt. It should be noted that only the alleles of diploid organisms conform in this way.

When crossing the heterozygous alleles with each other, a first generation F1 branch will be obtained where all individuals will have the same genetic configuration"Tt".

For this reason, all individuals will have the same appearance with each other and with respect to one of their parents (Rechtman, 2004).

What Is Mendel's First Law?  1

The genetic relationship in the Punnett Table, according to Mendel's first Law, manifests itself as a relation of statistical probabilities.

In the case of mixing between pure individuals, the odds of the F1 generation having the same appearance as one parent is 100%.

References

  1. Bailey, R. (February 11, 2017). Co . Search results for Diploid Cells and Reproduction: thoughtco.com
  2. Bortz, F. (2014). Chapter Five: Mendel's Laws and Genes. In F. Bortz, The Laws of Genetics and Gregor Mendel (Pages 44-45). New York: The Rosen Publishing Group.
  3. Hasan, H. (2005). Mendel and the Laws of Genetics. New York: The Rosen Publishing Group.
  4. Mendel, G., & Corcos, A.F. (1966). Offspring of Hybrids. In G. Mendel, A. F. Corcos, & F. V., Gregor Mendel's Experiments on Plant Hybrids: A Guided Study (Pages 117-120). New Brunswick: Rutgers University Press.
  5. Rechtman, M. (2004). Chapter 11: Mendelian Genetics. In M. Rechtman, CliffsStudySolver: Biology (Page 224). Hoboken: Wiley Publishing, Inc.
  6. Starr, C., Evers, C., & Starr, L. (2011). Mendel Pea Plants and Inheritance Patterns. In C. Starr, C. Evers, & L. Starr, Biology: Concepts and Applications (Pp. 190-191). Belmont: Cengage Learning, Inc.
  7. com. (August 20, 2015). Study.com . Obtained from Punnett Square: Definition & Example: study.com


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