Jumpstart into the world of Genetics: What is an Allele?
Have you ever heard about good genes or bad genes? You probably know about what a gene is but have you ever heard about an Allele?
An Allele is one or more versions of a gene represented by capital or lower case letter.
Dominant alleles are represented by a capital letter.
Recessive alleles are represented by a lowercase letter
Now I am going to talk about dominant and recessive alleles in detail using Gregor Mendel’s pea plants experiment. Pea plants are known to have several different phenotypes (visible traits). The main phenotype that was observed was color. There were two different colors of peas- green and yellow. When a 1st generation (F1) plant producing green peas was crossed with a plant that produced yellow peas, all of the offsprings (F2) had green peas. But when the offsprings (F2) were crossed, only 75% of their offsprings (F3) were green and the remaining 25% were yellow. This can be explained using dominant and recessive alleles.
In short, a dominant allele is an allele that can mask a recessive allele and a recessive allele can not have a dominant allele present to show itself. So the green peas were able to mask the yellow peas and there had to have only the yellow allele to be a yellow pea. I know that is confusing. Let me show it to you in a Punnett Square, the F1 green peas would be represented as a G (in green), as the yellow peas would be represented as g (in orange). First, the parent’s genotypes (set of alleles) are written across the top and sides for this scenario both of the pea plants are true-bred or homozygous (both alleles are the same).
Next what you need to do is bring the Alleles down or to the right (follow the arrows).
When it is filled out, it should look like this.
All of the F2 offspring are heterozygous (have 2 different alleles). What does that mean? If you recall, one of the things I said before is that dominant alleles mask recessive alleles and capital letters represent dominant alleles. All of the phenotypes possible from this cross are green. The capital G (green) masks the lowercase g (yellow). Now let’s try crossing two of the F2 offspring from this cross. Let’s start by putting the F2 genotypes on the top and side.
Then follow the arrows.
Finish the cross
Even though all of the F2 pea plants were green, there is a 25% chance F3 generation of peas could turn out yellow.
I hope this article gives you enough information about Alleles to help jumpstart interest in genetics.
Hello! My name is Aadhi Sekhar and I am a sophomore at Neuqua Valley High School, Naperville, Illinois and I am very interested in the science fields. I take extra interest in genetics and biology. If there is something incorrect or that could be changed in this article, please feel free to email me at aadhi@sekhar.net
