The First generation subsidiary Is a concept developed by genetics, defined as the offspring that results from the crossing of two homozygous organisms, one being dominant and the other recessive. It is identified with the letter F and the number 1, thus: F 1.
A homoc Igoto is that organism that possesses identical alleles (forms that can take a gene). Genetics is the part of Biology in charge of studying everything related to heredity.
The precursor of this discipline is Gregor Mendel , Who performed the crosses with pea and flower plants, where results were obtained on offspring, which depended on the characteristics of the parents.
Other scientists did post-Mendel experiments and concluded that genes determined the characteristics of phenotype (physical traits) and genotype (gene pool).
Mixed results were obtained by combining pure and combined species, reaching conclusions about the role of dominant alleles and recessive alleles.
In male and female gametes are inheritable characteristics, that the first filial generation (F 1 ) receives. It is necessary to understand the crossing of pure and hybrid species, as detailed:
Exercise N ° 1
They have a red rose (RR, dominant character) and a white rose (rr, recessive character). It is required to know what would be the result of crossing both.
They are denoted with 2 capital letters, the color of each type of rose:
Progenitors
F 1
The result comprises the 4 roses are red because of their dominant character, but it has a white color in its recessive character, in 100% of the offspring. They are hybrids.
The recessive character will appear in the second filial generation, when they cross with another progenitor of similar phenotypic characteristics.
This Exercise represents the second law of Mendel, since the recessive character is hidden in F 1, But when crossed with a similar flower there is the possibility that it appears.
Further phenotype characteristics (color and texture) can be added, as shown below:
Exercise # 2
They have two grains of beans, one of green and smooth (VVLL, dominant), the other yellow and rough (vvrr, recessive).
Progenitors
As each grain has color and texture, the possible combinations are made:
- Male: VL, VL, vL, vL.
- Female: VL, VL, vL, vL.
F 1
The results obtained are detailed, expressed in absolute frequency and relative frequency, for the 16 crossing possibilities:
- 9 green and smooth grains accounted for 56.25% of offspring.
- 3 green and rough grains were equivalent to 18.75% of the offspring.
- 3 yellow and smooth beads made up 18.75% of the result.
- 1 yellow and rough grain represented 6.25% of F 1 .
As in Exercise No. 1, it can be seen that the recessive characters, hidden in F 1 , Are more likely to emerge in second-generation subsidiary.
The possibilities of human offspring can be estimated, taking into account possible phenotype and genotype characteristics.
For this, an exercise will be performed on the union of progenitors who are carriers of the gene of color blindness:
Exercise N ° 3
A man with normal vision (D), bearer of the recessive gene of Daltonismo (X D Y D ) And a woman with normal vision (D), carrier of the recessive gene of Daltonismo (X D X D ).
It is necessary to know what are the chances of having offspring with the recessive gene of active color blindness.
Progenitors: X D Y D X D X D
The results of the offspring possibilities of the parent's union are:
F 1 : X D X D , X D X D , X D Y D , X D Y D
It is observed in F 1 That 1 man of the 4 descendants could have active the recessive gene of color blindness, equivalent to 25% of the possibilities. 1 woman leaves with normal vision without being a carrier of color blindness, equivalent to 25% of the results. There will be 1 man and 1 woman with normal vision but carriers of color blindness.
The man with color blindness, if he obtained offspring with a woman with normal vision and carrier of said gene, the second filial generation would have 50% chances of having offspring with the recessive gene of active color blindness.
We look for ways to estimate the possibilities of offspring, as detailed:
Exercise # 4
Between a man with the color of blue eyes (X N Y N ), Which is a recessive character and a woman with black eyes (X N X N ), As dominant but carrying the blue color, it is necessary to know the first subsidiary generation (F 1 ), The number of descendants with the active recessive character.
Progenitors: X N Y N X N X N
From the union of the parents, the results of the possibilities of descent can be obtained:
F 1 : X N X N , X N X N , X N Y N , X N Y N
It can be concluded that 2 descendants, 1 woman and 1 man, would have blue eyes while the other 2 would have black but bearers of the recessive character.
In the case of cattle, we have that horns are a recessive feature. The following statement is presented:
Exercise N ° 5
The male has as dominant character not having horns and possesses the recessive gene of the horns (X C Y C ) And the female has active the recessive character of the horns (X C X C ). It requires knowing how many hornless males in F1.
Progenitors: X C Y C X C X C
From the union of male and female gametes, you can obtain the results of the possibilities of descent, you have:
F 1 : X C X C , X C X C , X C Y C , X C Y C
The results show that half of the offspring are carriers of the recessive gene of the horns, whereas the other half has active the recessive character of the horns.
In f 1 They combine all the characteristics, dominant and recessive, of their parents. In this way we can establish the different possibilities in which the genotype and phenotype combined in living beings could result.
Likewise, it can be deduced how the result of the second subsidiary generation could be if they have the same dominant and recessive characteristics.
Genetics has allowed progress in agriculture to obtain better products in livestock to specify the options of obtaining cattle in the best conditions for production and breeding and in medicine to study hereditary diseases that could affect the human being.
Genetic studies in people who decide to procreate in a planned way, allows them to evaluate the possibilities that could affect positively (eye color, skin, hair) and negatively to their first filial generation (F 1 ).
Such is the case of diseases such as hemophilia, recessive character, which is suffered only by men and women are carriers.
References
- Genotype, Phenotype, Homozygous, Heterozygous, Dominant, Recessive, Allele and Locus. Recovered from: Sites.google.com.
- Lecture 1: Mendel's Laws. Recovered from: kmb.prf.jcu.cz.
- Mendel's Laws of Inheritance and Exceptions to the Laws. Retrieved from: eagri.tnau.ac.in.
- Serrano, L. et al. Genetic Basis of Evolution . Mexico City, Colegio Nacional de Bachilleres.
- Valega, O. (2014). The Laws of Mendel . Argentina, Beekeeping Don Guillermo.