The basics of genetics, how does it work? Part 1

In this lesson we are going to visit some very,

very basic issues which are the ones that we studied at the given moment in our life: the Mendel’s law and to understand the basics of the genetics of simple traits. So, the idea is to understand how genetic works and why many cases we put as examples of genetic diseases and to understand the impact of these diseases for humans. The basic idea is how a single gene may be at the base of a trait. This is what Mendel studied with the peas and he did very interesting and very accurate work on counting the traits and how these traits went from one generation to the next.

So, he put together the first, the initial laws of inheritance and his work was forgotten then rediscovered and today with the molecular vision we have of genetics, we can say that Gregor Mendel was totally right in the way he outlined the bases of heredity. How a single gene may be at the base of a trait? So, we have to see what we mean by a trait. A trait may be at the molecular level just looking at the basic gene action, which protein is going to be produced for example, we can go into the physiology and see the effect on the function or the whole individual state of health.

Here it’s very important to try to make the relationship between the genotype and the phenotype. This is something to go from the genetic information to the physical feature

that is what nowadays in biology most people are working: the details on how the phenotype is constructed given the information of the genome.

Some very basic concepts: alleles –we have been dealing already with that– the different variants of a gene. And these alleles may be dominant or recessive. When they’re dominant means that both, the heterozygotes and the homozygotes, they have the same phenotype and in general we put the capital letter for them. And the recessive is the one that you need two copies to show the phenotype, small r andsmall r.

Let’s visit the typical case of Mendel: the peas in which he saw two different forms, two different qualities in the seeds, in the plant, in the flower… In all the cases he was able to work out how the transmission was, and this is the way in general we see the transmission.

For example, in this case we have one trait which is the color –that may be yellow (Y) or may be green (y), big(Y): Y is dominant on small y. So, meaning that to have a pea green the individual must have small and small y, and having a single big Y is enough to be yellow. So, this is the way of understanding how we go from genotype to phenotype for this very, very simple case.