13. Mendelian Genetics
Genotype vs. Phenotype
Video duration:
6mRelated Videos
Related Practice
Skip to main content
So now that we've distinguished between the dominant and the recessive alleles in our last lesson video, in this video, we're going to distinguish between the genotype and the phenotype. And so the genotype, as its name implies with the root gene in it, is going to be the genetic combination of alleles in an individual organism. And so in diploid organisms that have 2 copies of every gene or 2 alleles, the genotype is always going to be written as a pair of letters. Now there are homozygous genotypes, and there are also heterozygous genotypes. Now the root homo is a root that means the same, And so it's no surprise that homozygous genotypes are going to be organisms that have 2 identical alleles for the same exact gene. And so the genotype could have 2 identical dominant alleles or 2 capital y's, or the genotype could have 2 identical recessive alleles or 2 lowercase y's. And so, the 2 capital y's that are identical here would be homozygous dominant, and the 2 lowercase y's that are identical would be homozygous recessive, and we distinguish between those down below in our image. Now the hetero zygous genotype, the root 'hetero', means different, and so it's no surprise that heterozygous genotypes are going to be individuals that have 2 different alleles for the same gene. And so for example, having a dominant allele and a recessive allele, those are 2 different alleles, would create a heterozygous genotype. And so if we take a look at our image down below, notice that the left column here has the genotype, the combination of alleles and an individual. And so notice that the first two, the numbers 12 here correspond with the number 12 down below. They are referring to homozygous genotypes, meaning that the individual has 2 identical alleles. Now the top one here is referring to a homozygous dominant genotype because it has 2 capital Y's, 2 dominant alleles. And notice that the individual down here with the homozygous, has a homozygous recessive recessive genotype because it has 2 lowercase wise or 2 recessive alleles. And then of course this third genotype that we have down here has 1 dominant allele and one recessive allele, one capital y and one lowercase y, which means that it has 2 different alleles for the same gene and it is going to be a heterozygous genotype. And so again the genotype is always gonna be written as a pair of letters. It's the genetic combination of alleles. But what is that exactly is the phenotype? Well, the phenotype, as its name implies with the pH here in front of it, is going to be the physically expressed trait that results from the genotype. And so the phenotype is going to be a physical expression of the genotype. And so, it is going to be physically expressed in this scenario as either the yellow color of the p or the green color of the p. And so you can see down below in our chart, we have the phenotype over here on the right column. And notice that the homozygous dominant genotype leads to a yellow color phenotype. Notice that the homozygous recessive, genotype leads to a green color phenotype. And notice that the heterozygous genotype leads to a yellow color phenotype. And so the reason that the heterozygous, genotype leads to a yellow color and not a green color is because, again, the dominant allele will dominate and exert its effect over the recessive allele when they are both together. And the recessive allele is going to be masked when it's in the presence of the dominant allele. And so the dominant allele is going to dominate and create a p with yellow color. And so just by visually looking at the color of these p's, we would not be able to distinguish between the homozygous dominant and the heterozygous pea because they both have yellow colored peas. And so we would not be able to visually distinguish between them. However, there are ways that we can test to see what the genotype is of plants that have these specific phenotypes, and we'll get to talk more about that later in our course. But for now, this here concludes our lesson on the difference between the genotype and the phenotype. How the genotype is a genetic combination of alleles or a pair of letters, whereas the phenotype is gonna be a physically expressed cherry, such as the color of a specific pea. And so we'll be able to get some practice as we move forward in our course. So I'll see you all in our next video.
03:39
