Genotype vs. Phenotype - Online Tutor, Practice Problems & Exam Prep

Understanding the difference between genotype and phenotype is crucial in genetics. The genotype represents the genetic combination of alleles, written as pairs of letters, while the phenotype is the physical expression of these traits, such as pea color. Dominant alleles, symbolized by capital letters, mask the effects of recessive alleles, represented by lowercase letters. For example, a homozygous dominant genotype (YY) and a heterozygous genotype (Yy) both result in a yellow phenotype, demonstrating the dominance of the yellow allele over the green allele (yy).

Dominant vs. Recessive Alleles

In this video, we're going to begin our lesson on genotype versus phenotype. But before we can define genotype and phenotype, it's first helpful to distinguish between the dominant and recessive alleles. Recall from our previous lesson videos that alleles are really just different versions of specific genes. It turns out that alleles can be either dominant or recessive. The dominant allele, as its name implies, is going to be an allele that dominates and exerts its effects whenever it is present. The dominant allele is usually symbolized with a capital letter. Now, the recessive allele, on the other hand, is, as its name implies, recessive, meaning that it's going to have no effect if a dominant allele is present. The recessive allele can only have its effect when there is no dominant allele. The recessive allele is symbolized using a lower case letter.

As Gregor Mendel was studying these pea plants, what he realized is that the allele for yellow peas was actually dominant to the allele for green peas. This, of course, means that the yellow allele was going to be the dominant allele, and the green allele is going to be the recessive allele. If we take a look at our image down below, we can better distinguish between dominant and recessive alleles. Notice over here we're showing you that the dominant allele here is going to be represented using a capital letter. Here we're using the capital letter y to represent the dominant allele for yellow pea color. You can see here that this dominant allele really looks pretty dominant here in this image with these large muscles. The recessive allele over here, on the other hand, is represented using lowercase letters. So we have the lowercase letter y, and the recessive allele is not going to be dominant. It is not going to exert its effect if a dominant allele is present. You can see that the recessive allele here is kind of looking afraid of the dominant allele. Again, the recessive allele here would be the allele for green pea color.

What we'll notice moving forward is that the dominant allele here is going to mask or hide the effect of the recessive allele whenever the dominant allele is present. This concludes our introduction to the difference between dominant and recessive alleles, and we'll be able to get some more practice applying these concepts as we move forward in our course. In our next video, we'll talk more about the difference between genotype and phenotype. So I'll see you all there.

An allele that exerts its effects whenever it is present is:

• A. Recessive.
• B. Heterozygous.
• C. Dominant.
• D. Homozygous.
• E. Homologous.

Genotype & Phenotype

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. The genotype, as its name implies with the root gene in it, is the genetic combination of alleles in an individual organism. In diploid organisms that have 2 copies of every gene or 2 alleles, the genotype is always written as a pair of letters. There are homozygous genotypes, and there are also heterozygous genotypes. The root homo means the same, and so homozygous genotypes are organisms that have 2 identical alleles for the same exact gene. 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. 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. The heterozygous genotype, the root 'hetero', means different, and so it's no surprise that heterozygous genotypes are individuals that have 2 different alleles for the same gene. Having a dominant allele and a recessive allele, which are 2 different alleles, would create a heterozygous genotype. If we take a look at our image down below, notice that the left column here has the genotype, the combination of alleles in an individual. Notice that the first two, numbers 12 here correspond with number 12 down below. They are referring to homozygous genotypes, meaning that the individual has 2 identical alleles. The top one here is referring to a homozygous dominant genotype because it has 2 capital Y's, 2 dominant alleles. Notice that the individual down here with the homozygous has a homozygous recessive genotype because it has 2 lowercase Y's, 2 recessive alleles. This third genotype has 1 dominant allele and 1 recessive allele, 1 capital Y and 1 lowercase y, which means that it has 2 different alleles for the same gene and it is a heterozygous genotype. Again, the genotype is always written as a pair of letters. It's the genetic combination of alleles.

What is the phenotype? The phenotype, as its name implies with the pH, is the physically expressed trait that results from the genotype. The phenotype is the physical expression of the genotype. It is physically expressed in this scenario as either the yellow color of the pea or the green color of the pea. You can see down below in our chart, we have the phenotype on the right column. Notice that the homozygous dominant genotype leads to a yellow color phenotype. The homozygous recessive genotype leads to a green color phenotype. Notice that the heterozygous genotype leads to a yellow color phenotype. The reason that the heterozygous genotype leads to a yellow color and not a green color is that the dominant allele will dominate and exert its effect over the recessive allele when they are both together. The recessive allele is going to be masked when it's in the presence of the dominant allele. The dominant allele is going to dominate and create a pea with a yellow color. Just by visually looking at the color of these peas, we would not be able to distinguish between the homozygous dominant and the heterozygous pea because they both have yellow-colored peas. 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 going to be a physically expressed trait, such as the color of a specific pea. 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.

If the two alleles for a particular gene are identical the gene pair is:

• A. Homozygous.
• B. Heterozygous.
• C. Recessive.
• D. Homologous.
• E. Dominant.
• F. Dissimilar.

If an individual is homozygous for a particular trait:

• A. Each parent contributed a different allele for that trait.
• B. One parent contributed two different alleles for that trait.
• C. Each parent contributed the same allele for that trait.
• D. One parent contributed two copies of the same allele for that trait.

Mendel's pea plants can have yellow peas or green peas. Mendel found the yellow pea color allele to be dominant over the green pea color allele. What does this mean?

• A. The yellow allele masks the effects of the green allele in an individual heterozygous for pea color.
• B. Both individuals who are heterozygous and homozygous dominant for pea color will have yellow peas.
• C. Only individuals who are homozygous recessive for pea color will have green peas.
• D. The green pea color allele can be found in some individuals but not expressed.
• E. All of the above.

Here’s what students ask on this topic:

What is the difference between genotype and phenotype?

The genotype refers to the genetic makeup of an organism, specifically the combination of alleles it possesses. In diploid organisms, this is represented as a pair of letters, such as YY, Yy, or yy. The phenotype, on the other hand, is the observable trait that results from the genotype. For example, in pea plants, a genotype of YY or Yy results in a yellow phenotype, while a genotype of yy results in a green phenotype. The dominant allele (Y) masks the effect of the recessive allele (y), influencing the phenotype.

How do dominant and recessive alleles affect phenotype?

Dominant alleles exert their effects whenever they are present, masking the effects of recessive alleles. For instance, in pea plants, the allele for yellow peas (Y) is dominant over the allele for green peas (y). Therefore, both the homozygous dominant genotype (YY) and the heterozygous genotype (Yy) result in a yellow phenotype. The recessive allele (y) only expresses its effect when the dominant allele is absent, as in the homozygous recessive genotype (yy), which results in a green phenotype.

What are homozygous and heterozygous genotypes?

Homozygous genotypes have two identical alleles for a specific gene. This can be either homozygous dominant (YY) or homozygous recessive (yy). Heterozygous genotypes, on the other hand, have two different alleles for the same gene (Yy). In the case of pea plants, a homozygous dominant genotype (YY) and a heterozygous genotype (Yy) both result in a yellow phenotype, while a homozygous recessive genotype (yy) results in a green phenotype.

Can you visually distinguish between homozygous dominant and heterozygous individuals?

No, you cannot visually distinguish between homozygous dominant (YY) and heterozygous (Yy) individuals based solely on their phenotype if the dominant allele masks the recessive one. For example, in pea plants, both YY and Yy genotypes result in a yellow phenotype. To determine the exact genotype, genetic testing or breeding experiments would be necessary.

Why is understanding genotype and phenotype important in genetics?

Understanding genotype and phenotype is crucial in genetics because it helps explain how traits are inherited and expressed. The genotype provides the genetic blueprint, while the phenotype is the observable outcome. This knowledge is essential for studying genetic inheritance, predicting trait distribution, and understanding genetic disorders. It also forms the basis for advanced topics like genetic engineering and personalized medicine.