Relationships Between Genes, Genotypes and Phenotypes - Biology LibreTexts
Each gene occupies a specific locus (so the terms locus and gene are often used interchangeably). Each locus will have an allelic form (allele). differences between chromosomes, alleles, genes, and locus. The following simplified diagram should help clarify the proper usage of these terms. chromosome. Since the gene for albinism is recessive, it only shows up in the phenotype of homozygous The alleles for a trait occupy the same locus or position on homologous . There is a correlation between the amount of sunlight that children are.
And actually it doesn't have to just be even for a protein. That gets processed so you could actually lose some sections of it, but you go to messenger RNA and then that messenger RNA, every three of these base pairs is a Codon. Let me, so let's say that's one codon. One, two, three, that's another codon. One, two, three, each of those-- Maybe I'll draw them next to each other.
Each of of them codes for an amino acid that is kind of connected together to form, connected together to form a protein. So that's one amino acid right over there. This could be another amino acid right over there. We can keep going on and on and on and on. You could have another Amino Acid right over here, and then they all bond to each other and they're brought actually to the mRNA from a, by a functional RNA group.
And so there are functional things other than proteins that this could code for. So you can have tRNA and we've seen this before in previous videos. It's this little squiggly line, matches up the the appropriate Codon, and then puts that Amino Acid in place. So RNA doesn't have to only play this kind of in between messenger function.
It actually can play a functional or a structural role. In fact there are theories that the earliest life, the most primitive life was nothing but self replicating RNA and then the systems became more, and more, and more complicated and complex until eventually you end up with things like redwood trees and hippopotami.
Elephants, but whatever else, but it all started with potentially self replicating RNA.
Some people say it might be some type of proteins are able to replicate, who knows, but RNA is definitely, is definitely an interesting character in this. So each of these Genes they can code for a type of protein or even a functional RNA.
That's what a Gene is. Now what about an Allele? When the Allele is a specific variation of the Gene. So for example, let's say that you look at the at the same stretch of DNA. We're both human beings and we have for the most part very similar DNA. So this is-- Actually let me straighten it out. Now we're both human beings and most of our genetic material is fairly similar, but we might have variations in how this Gene is coded.
For example, you might have or I might have a let's say, I have a an Adenine right there, but right at that exact spot you might have a different base. You might have a, I don't know, you might have a, you might have-- Actually let me just-- You might have a Thymine right over there. So it's encoding for a protein, or you know, functional RNA that's playing the same role.
Maybe it has a role in the immune system or role in your skin color or role in how your brain develops, but there's a variation. There's a variation in how it's coded. Now some of these variations which could arise through mutations, it might not have any impact in the function of the eventual protein that gets constructed. You might just have a different Amino Acid sometimes. However, many different systems of genetic symbols are in use.
The most common are shown in Table 3. Also note that genes and alleles are usually written in italics and chromosomes and proteins are not.
Examples of symbols used to represent genes and alleles. Examples Interpretation A and a Uppercase letters represent dominant alleles and lowercase letters indicate recessive alleles.
Mendel invented this system but it is not commonly used because not all alleles show complete dominance and many genes have more than two alleles.
How are the terms gene, locus, and allele related? | Socratic
In incomplete dominance also called semi-dominance, Figure 3. For example, alleles for color in carnation flowers and many other species exhibit incomplete dominance. We say that the A1 and the A2 alleles show incomplete dominance because neither allele is completely dominant over the other. An example of co-dominance is found within the ABO blood group of humans.
What’s the Difference Between a Gene and an Allele?
People homozygous for IA or IB display only A or B type antigens, respectively, on the surface of their blood cells, and therefore have either type A or type B blood Figure 3.
Notice that the heterozygote expresses both alleles simultaneously, and is not some kind of novel intermediate between A and B. Co-dominance is therefore distinct from incomplete dominance, although they are sometimes confused. The IA and IB alleles show co-dominance.
The IA allele is completely dominant to the i allele. The IB allele is completely dominant to the i allele.
AN It is also important to note that the third allele, i, does not make either antigen and is recessive to the other alleles. People homozygous for the i allele have type O blood.