The Subsidiary generation Is the offspring resulting from controlled pairing of parental generation. It is usually given between different parents with Genotypes Relatively pure (Genetics, 2017). It is part of the laws of genetic inheritance of Mendel.
The filial generation is preceded by the parental generation (P) and is marked with the symbol F. In this way, the filial generations are organized in a mating sequence.
In such a way that each one is attributed the symbol F followed by the number of its generation. That is, the first subsidiary generation would be F1, the second F2, and so on (BiologyOnline, 2008).
The concept of filial generation was first proposed in the 19th century by Gregor Mendel . This was an Austro-Hungarian monk, naturalist and catholic who, within his monastery, carried out different experiments with peas to determine the principles of genetic inheritance.
During the nineteenth century it was believed that the offspring of the parental generation inherited a mixture of the genetic characteristics of the parents. This hypothesis posed genetic inheritance as two mixing liquids.
However, Mendel's experiments, carried out over 8 years, showed that this hypothesis was a mistake and explained how genetic inheritance actually takes place.
For Mendel it was possible to explain the principle of filial generation when cultivating common pea species, with markedly visible physical characteristics such as color, height, pod surface and seed texture.
In this way, only individuals that had the same characteristics were paired with the objective of purifying their genes and then initiating the experimentation that would give rise to the theory of filial generation.
The principle of filial generation was only accepted by the scientific community during the twentieth century, after the death of Mendel. For this reason, Mendel himself maintained that someday his time would come, if it were not in life (Dostál, 2014).
The Mendel Experiments
Mendel studied different types of pea plants. He noticed that some plants had purple flowers and other white flowers. He also observed that pea plants self fertilize, although they can also be inseminated through a process of cross fertilization called hybridization . (Laird & Lange, 2011)
To begin his experiments, Mendel needed to have individuals of the same species that could be matched in a controlled manner and give way to fertile offspring.
These individuals had to have marked genetic characteristics, so that they could be observed in their offspring. For this reason, Mendel needed plants that were purebred, that is, that his offspring had exactly the same physical characteristics as his parents.
Mendel dedicated more than 8 years to the process of fertilization of pea plants until obtaining pure individuals. In this way, after many generations, the purple plants only gave birth to purple plants and the white plants only gave white offspring.
Mendel's experiments began by crossing a purple plant with a white plant, both purebred. According to the hypothesis of the genetic inheritance contemplated during the nineteenth century, the offspring of this crossing should give rise to lilac flowers.
Mendel, however, observed that all of the resulting plants were deep purple. This first filial generation was denominated by Mendel with the F1 symbol. (Morvillo & Schmidt, 2016)
Crossing members of the F1 generation with each other, Mendel observed that his offspring were intense purple and white in a ratio of 3: 1, with a greater predominance of purple. This second subsidiary generation was marked with the symbol F2.
The results of the experiments of Mendel were later explained according to the Law of Segregation.
Law of Segregation
This law indicates that each gene has different Alleles . For example, a gene determines the color in the flowers of the pea plants. Different versions of the same gene are known as alleles.
Pea plants have two different types of alleles to determine the color of their flowers, one allele that gives them purple and one that gives them the color white.
There are alleles Dominant And recessive. In this way, it is explained that in the first generation (F1) all plants gave purple flowers, because the purple color allele is dominant over the white color.
However, all individuals belonging to the F1 group have the white recessive allele, which allows, when paired with each other, to give rise to both purple and white plants in a 3: 1 ratio, where the purple color is dominant On white.
The law of segregation is explained in the Punnett table, where there is a parental generation of two individuals, one with dominant alleles (PP) and one with recessive alleles (pp). Being paired in a controlled manner should result in a first generation filial or F1 where all individuals have both dominant and recessive alleles (Pp).
When the individuals of the F1 generation are mixed together, four types of alleles (PP, Pp, pP and pp) are given, where only one in four individuals will manifest the characteristics of the recessive alleles (Kahl, 2009).
Individuals whose alleles are mixed (Pp) are known as Heterozygotes And those with equal alleles (PP or pp) are known as Homozygotes . These allele codes are known as the genotype while the visible physical characteristics resulting from that genotype are known as phenotype.
The Mendel Segregation Law states that the genetic distribution of a subsidiary generation is dictated by the law of probability.
In this way, the first generation or F1 will be 100% heterozygotes and the second generation or F2 will be 25% dominant homozygotes, 25% recessive homozygotes and 50% heterozygotes with both dominant and recessive alleles. (Russell & Cohn, 2012)
In general, the physical characteristics or phenotype of individuals of any species are explained by Mendel's genetic inheritance theories, where the genotype will always be determined by the combination of recessive and dominant genes from parental generation.
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- Kahl, G. (2009). The Dictionary of Genomics, Transcriptomics and Proteomics. Frankfurt: Wiley-VCH. Retrieved from Mendel's Laws.
- Laird, N.M., & Lange, C. (2011). Principles of Inheritance: Mendel's Laws and Genetic Models. In N. Laird, & C. Lange, The Fundamentals of Modern Statistical Genetics (pp. 15-28). New York: Springer Science + Business Media,. Retrieved from Mendel's Laws.
- Morvillo, N., & Schmidt, M. (2016). Chapter 19 - Genetics. In N. Morvillo, & M. Schmidt, The MCAT Biology Book (pp. 227-228). Hollywood: New Press.
- Russell, J., & Cohn, R. (2012). Punnett Square. Book on Demand.