The filial generation is the offspring resulting from the controlled mating of the parental generation. It usually occurs between different parents with relatively pure genotypes (Genetics, 2017). It is part of Mendel's laws of genetic inheritance.
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 filial 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 19th century it was believed that the offspring of the parental generation inherited a mixture of the genetic characteristics of the parents. This hypothesis posited genetic inheritance as two liquids that mix.
However, Mendel's experiments, carried out over 8 years, showed that this hypothesis was wrong and explained how genetic inheritance actually takes place.
For Mendel, it was possible to explain the principle of filial generation by growing common pea species, with markedly visible physical characteristics, such as color, height, pod surface, and seed texture.
In this way, he mated only individuals that had the same characteristics in order to purify their genes to later start 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 20th century, after Mendel's death. For this reason, Mendel himself maintained that one day his time would come, even if it were not in life (Dostál, 2014).
Mendel's experiments
Mendel studied different types of pea plants. He observed that some plants had purple flowers and other white flowers. She also observed that pea plants are self-fertilizing, although they can also be inseminated through a process of cross-fertilization called hybridization. (Laird & Lange, 2011)
To start his experiments, Mendel needed to have individuals of the same species that could be mated in a controlled way and give way to fertile offspring.
These individuals had to have marked genetic characteristics, in such a way that they could be observed in their offspring. For this reason, Mendel needed plants that were purebred, that is, their offspring had exactly the same physical characteristics as their parents.
Mendel dedicated more than 8 years to the process of fertilizing pea plants until obtaining pure individuals. In this way, after many generations, the purple plants only gave birth to purple plants and the white ones only gave white offspring.
Mendel's experiments began by crossing a purple plant with a white plant, both purebred. According to the hypothesis of genetic inheritance contemplated during the 19th century, the offspring of this cross should give rise to lilac flowers.
However, Mendel observed that all the resulting plants were deep purple in color. This first generation subsidiary was named by Mendel with the symbol F1. (Morvillo & Schmidt, 2016)
When crossing the members of the F1 generation with each other, Mendel observed that their offspring had an intense purple and white color, in a ratio of 3: 1, with the purple color being more predominant. This second generation subsidiary was marked with the symbol F2.
The results of Mendel's experiments were later explained according to the Law of Segregation.
Segregation law
This law indicates that each gene has different alleles. For example, one gene determines the color in the flowers of 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 the color purple and another that gives them the color white.
There are dominant and recessive alleles. In this way it is explained that in the first filial generation (F1) all the plants gave purple flowers, since the allele of the purple color is dominant over the white color.
However, all individuals belonging to the F1 group have the recessive allele of the white color, which allows that, when paired with each other, they give rise to both purple and white plants in a 3: 1 ratio, where the purple color is dominant. on the white.
The law of segregation is explained in the Punnett square, where there is a parental generation of two individuals, one with dominant alleles (PP) and the other with recessive alleles (pp). When paired in a controlled way, they must give rise to a first filial or F1 generation where all individuals have both dominant and recessive alleles (Pp).
When mixing the individuals of the F1 generation with each other, there are four types of alleles (PP, Pp, pP and pp), where only one in four individuals will manifest the characteristics of recessive alleles (Kahl, 2009).
Punnett square
Individuals whose alleles are mixed (Pp) are known as heterozygous and those with the same alleles (PP or pp) are known as homozygous. These allele codes are known as the genotype while the visible physical characteristics resulting from that genotype are known as the phenotype.
Mendel's Law of Segregation holds that the genetic distribution of a filial generation is dictated by the law of probabilities.
In this way, the first generation or F1 will be 100% heterozygous and the second generation or F2 will be 25% homozygous dominant, 25% homozygous recessive and 50% heterozygous 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 theories of genetic inheritance, where the genotype will always be determined by the combination of recessive and dominant genes from the parental generation.
References
- (2008, 10 9). Biology Online. Retrieved from Parental generation: biology-online.org.
- Dostál, O. (2014). Gregor J. Mendel - Genetics Founding Father. Plant Breed, 43-51.
- Genetics, G. (2017, 02 11). Glossaries Retrieved from Generación Filial: glosarios.servidor-alicante.com.
- Kahl, G. (2009). The Dictionary of Genomics, Transcriptomics and Proteomics. Frankfurt: Wiley-VCH. Retrieved from Mendel's Laws.
- Laird, NM, & 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: Nova Press.
- Russell, J., & Cohn, R. (2012). Punnett Square. Book on Demand.