FIRST GENERATION FILIAL (F1): CHARACTERISTICS, EXAMPLES - BIOLOGY - 2024

The term first filial generation, abbreviated as F ₁, refers to the progeny resulting from a cross between two individuals called the parental generation - or generation P. In other words, they are the children of the first parents.

As the crosses progress, the term second generation filial, abbreviated F ₂, is used to refer to the progeny of the first generation. The second generation filial can also be obtained by self-fertilization.

This word is widely used in genetics when evaluating crosses between organisms and specifically when talking about the work of Gregor Mendel.

characteristics

Logically, there is no universal way to describe the first filial generation, since its genotypic and phenotypic characteristics depend on the parents that originated it and the type of dominance (complete, incomplete, codominance) of the study characteristic.

However, Mendel described certain observable patterns in the first filial generation, as will be seen in the following examples.

In a very general way, and only when dominance is complete, in the first filial generation the characteristic of one of the parents is observed.

Therefore, a dominant trait is defined as the characteristic expressed in the first filial generation and in the heterozygous condition. In contrast to a recessive trait that is not expressed in the first filial generation, but appears again in the second.

Examples

First generation subsidiary in

Gregor Mendel managed to enunciate his famous laws by evaluating different crosses in more than 28,000 pea plants belonging to the Pisum sativum species.

Mendel valued different observable characteristics in the plant, such as the shape of the seed, the color of the seed, the color of the flowers, the morphology of the pod, among others.

The first experiments consisted of monohybrid crosses, that is, only one character was taken into account.

When Mendel crossed pure lines of two organisms with contrasting characteristics - for example, a plant with green seeds and others with yellow seeds - he found that the entire first filial generation exhibited only the dominant character. In the case of seeds, the first filial generation only presented yellow seeds.

One of the most relevant conclusions of this experience is to understand that, although the first filial generation presents only the phenotype of one of the parents, it has inherited the “factors” from both parents. These so-called genetic factors, a term coined by Mendel, are genes.

By self-fertilizing this first filial generation, the recessive traits masked in the first generation appear again.

First filial generation in rabbits

In a certain species of rabbit, short hair (C) dominates over long coat (c). Note that if you want to know the phenotype of the cross between a long-haired and a short-haired rabbit, you also need to know their genotypes.

If they are pure lines, that is, a homozygous dominant rabbit (CC) with a homozygous recessive (cc), the first filial generation will be made up of heterozygous long-haired rabbits (Cc).

If the lines are not pure, a cross between a long-haired rabbit with a short-haired one (superficially identical to the previous one) may give different results. When the shorthair rabbit is heterozygous (Cc), cross half heterozygous offspring with short hair and the other half with long hair.

For the above crossing, it is not necessary to identify the genotype of the long-haired rabbit, since it is a recessive trait and the only way for it to be expressed is for it to be homozygous.

This same consideration can be applied to the example of peas. In the case of seeds, if the parents are not pure breeds, we will not obtain a totally homogeneous first filial generation.

First generation filial in aubergines

All the characteristics evaluated by Mendel exhibited a type of complete dominance, that is, the yellow color dominates the green, therefore in the first generation only the yellow phenotype is observed. However, there are other possibilities.

There are specific cases where the first filial generation does not exhibit the parental traits and "new" traits appear in the offspring that are intermediate between the parental phenotypes. In fact, some attributes can appear in the offspring although the parents do not have this characteristic.

This phenomenon is known as incomplete dominance and the fruit of the eggplant plant is an example of this. The homozygous of these fruits can be dark purple (the genotype is PP) or totally white (pp).

When two pure lines of plants with purple fruits are crossed with plants with white flowers, fruits of a purplish hue are obtained, intermediate between their parents. The genotype of this generation is Pp.

On the contrary, if the dominance of the fruit color were complete, we would expect to obtain a completely purple first generation filial.

The same phenomenon occurs in determining the color of the flowers of the Antirrhinum genus plant, popularly known as snapdragon.

Crosses of individuals with different blood groups

The phenotype does not refer only to the characteristics observable to the naked eye (such as the color of the eyes or hair), it can also occur at different levels, either anatomical, physiological or molecular.

It may be that in the first generation both alleles of the parents are expressed and this phenomenon is called codominance. MN blood groups follow this pattern.

The locus (physical position of the gene on the chromosome) MN codes for a certain type of antigens located on blood cells or erythrocytes.

If an individual with a genotype L ^M L ^M (they code for the M antigen) is crossed with another whose genotype is L ^N L ^N (they code for the N antigen), all individuals of the first filial generation will have the L ^M L genotype ^N and will express the two antigens equally.

Sex-linked inheritance

Certain genes that are located on the sex chromosomes must be taken into consideration. Therefore, the inheritance pattern of said characteristic deviates from those mentioned above.

The key to understanding what the outcome of the first filial generation will be is to remember that males receive the X chromosome from their mother and that the characteristic linked to that chromosome cannot be transmitted from the father to the male child.

References

1. Campbell, NA, & ​​Reece, JB (2007). Biology. Panamerican Medical Ed.
2. Cummings, MR, & Starr, C. (2003). Human heredity: principles and issues. Thomson / Brooks / Cole.
3. Griffiths, AJ, Wessler, SR, Lewontin, RC, Gelbart, WM, Suzuki, DT, & Miller, JH (2005). An introduction to genetic analysis. Macmillan.
4. Luker, HS, & Luker, AJ (2013). Laboratory exercises in Zoology. Elsevier.
5. Pierce, BA (2009). Genetics: A conceptual approach. Panamerican Medical Ed.