The 5 differences between genotype and phenotype

A summary of the differences between genotype and phenotype, basic concepts in Biology and Medicine.

Genetics explains all physiological phenomena of living beings, from the origin of life to evolutionary radiation in specific parts of history, to diseases, genetic conditions, facial features and much more. Each of our cells has DNA within it, and without it, cellular metabolism and existence itself would be impossible.

Although it may seem difficult to understand, the transformation of the genome's instructions into proteins encodes our external features. DNA, packaged as chromosomes within the cell, contains a series of nucleotides of great interest, namely in genes. These DNA sequences are "copied" (transcribed) into messenger RNA, which travels to the cytoplasm.

The messenger RNA is "read" (translated) by ribosomes, which assemble amino acids according to the order established by the genes, to give rise to the necessary proteins. Thus, the genome is transformed into living tissues.

With this express class on protein synthesis, we are ready to show you the differences between genotype and genotype. the differences between the genotype and the phenotypeThe differences between genotype and phenotype, what separates the genetic code from the individual characteristics.

The basics of genetics

All human cells are derived from the division of a zygote, a cell resulting from the union of a female gamete (egg) and a male gamete (sperm). Each gamete is haploid, which means that it has half of the expected genetic information (n=23). (n=23) to, when joined with its partner, give rise to a functional diploid organism (2n=46).

Our species is diploid and has 46 total chromosomes in the nucleus of each somatic cell, 23 from the mother and 23 from the father. Diploidy is a clear evolutionary adaptation, since by presenting "double" genetic information, we also have two copies of each gene. Each of the forms that a gene can acquire is known as an "allele", differentiated from the rest by its sequence. Thus, we inherit two alleles for each gene, we inherit two alleles for each gene, one from the father and the other from the mother..

What are the differences between genotype and phenotype?

This introduction was necessary, because from here on we are going to move into the realms of alleles, genes, traits and much more complex terms. Here are the differences between genotype and phenotype.

1. The genotype cannot be seen externally, but the phenotype can.

The genotype is the set of genetic information that a particular organism possesses in the form of DNA.. This includes genes, extragenic regions and sequences related to genes that do not encode proteins as such. In other words, the genotype is the set of nucleotides arranged in the form of the DNA double helix that differentiates us from the rest of the species and from other individuals of the same species.

On the other hand, the phenotype refers to the set of physical and behavioral traits that an individual exhibits based on its genotype (it is not an ethereal concept, but a visible one). However, in later sections we will see that the phenotype is not only the manifestation of the genotype, despite what is argued in generalist sources.

2. The phenotype is not only a product of the genotype.

Mendel's laws and Mendelian genetics have been very useful in paving the way for modern geneticists, but in many areas they fall short of the mark. Let's take an example: a pea can have an allele (a) that encodes a rough skin, while allele (A) encodes a smooth skin. The pea (aa) will be rough and the pea (AA) smooth, right?

So, what happens if we put the pea (AA) under water for 3 hours a day and its surface ends up becoming rough due to water stress? With this case, we want to exemplify that the genotype alone does not explain the phenotypeThe environment, nutrition and epigenetic mechanisms promote the appearance of variability beyond the alleles. A pea (AA) may have wrinkled skin because of environmental stressors, not because its genome dictates it.

The same premise holds when analyzing genetically identical individuals, such as twins (except for sporadic mutations). Although many hereditary disorders occur in both twins at the same time (such as personality disorders), sometimes one twin may have a psychiatric disorder and the other may not. The same is true for weight, skin tone, muscularity and many other things. If one leads a different lifestyle than the other and lives in a different region, he or she will naturally show a different genotype than his or her twin brother or sister.

3. A character is not always encoded by a single gene.

Generally speaking, an organism is said to be homozygous for a trait when both alleles (those on the chromosome of each parent) are the same.. In other words, if there is the possibility of inheriting a dominant (B) allele and a recessive (b) allele, an individual can be homozygous dominant (BB), homozygous recessive (bb) or heterozygous (Bb). In the latter case, the allele that is expressed will be the dominant allele (B).

In the most deterministic explanations of genetics, each pair of alleles (bb,BB or Bb) will encode the nature of a particular trait, such as eye color. Still, it is shocking to discover that a seemingly simple trait like eye color is influenced by more than 3 genes: EYCL1, EYCL2, EYCL3 (more than 6 alleles).

Anyway, some diseases are monogenici.e. they are explained by the dysfunction of one or both alleles within the same gene. Sickle cell anemia (mutations on chromosome 11), cystic fibrosis (mutations on chromosome 7) and hemochromatosis (mutations on chromosome 6) are some examples of monogenic diseases.

4. Genotype and phenotype do not always agree

If we continue with the train of thought of the previous example, we will discover that many hereditary diseases are autosomal recessive, that is, if there is a non-mutated allele (D), the one that is dysfunctional (d) will be masked. When a condition is recessive in nature, only the (dd) offspring will express it, while the (Dd) offspring will express it.while the (Dd) will be carriers or will show a much more attenuated signology.

For this reason we have said before that diploidy is an adaptive condition. When the gene on the chromosome of one of the parents (the mutated allele) fails, it is expected that the copy on the chromosome of the other parent will be able to compensate for the deficiency. In any case, there are some diseases that are dominant, and in them it is sufficient that one of the genes is mutated for the condition to manifest itself in its entirety.

5. Sometimes, the phenotype is more than the sum of its parts.

We have told you that a living being can be homozygous or heterozygous for a character. Heterozygotes always show the character encoded by the dominant allele (A), while the recessive allele (a) is masked.. However, as in everything in life, there are exceptions that confirm the rule.

Sometimes, alleles are codominant and are expressed at the same time, forming a character different from the sum of their parts. For example, if the gene for the coloration of the petals of a flower has variability in the form of a white allele (w) and a red allele (W), if both are codominant, the specimen (Ww) will have petals with both white and red spots.

Summary

As a small note, it is worth mentioning that all the alleles we have named have been given an arbitrary name for purely informative purposes, but they do not correspond to an established and standardized genetic designation in all cases. The purpose of using these symbols is to show that a recessive allele is represented by a lowercase letter and a dominant allele by a capital letter, nothing else.

Beyond technicalities, it is necessary to emphasize that the phenotype is not always the exact manifestation of the genotype. Environment, nutrition, exercise and epigenetic mechanisms (activation or inhibition of genes throughout life) also play an essential role in the variability of traits in the human population.