Incomplete Dominance vs. Codominance - Video Tutorials & Practice Problems
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1
concept
Incomplete Dominance
Video duration:
3m
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Video transcript
In this video we're going to begin our lesson on incomplete dominance versus codominance. We're gonna start off by introducing incomplete dominance in this video, and then later in a separate video, we'll introduce codominance. And so incomplete dominance is a pattern of inheritance where heterozygous individuals show a blended phenotype that is really just an intermediate of the phenotypes from the 2 alleles. And so in this example, what we're gonna look at is incomplete dominance and red and white flower cross, and how this incomplete dominance ends up making pink baby flowers. And so over here on the left hand side what we have is this little table of the specific allele and the phenotype that they lead to. And really there are only 2 alleles in this example. There is the r one allele which leads to a red flower phenotype, and then there is an r 2 allele which leads to a white flower phenotype. But notice that there is not a third allele here with incomplete fertilization of a red flower with a white flower, notice the red flower is homozygous for the r one allele and the white flower is heteros I'm sorry, homozygous for the r2 allele. When we perform this cross here, what we end up getting are heterozygous individuals. We get, r 1 and r 2 in each of these boxes. So we get a heterozygous allele. And again, remember the r one allele says make red flower and the r two allele says make white flower. However, when we have a heterozygous individual, it shows a blended phenotype that is an intermediate of the phenotypes from the 2 alleles. So instead of getting a red flower or a white flower with the heterozygous individual, we get a pink flower. And notice that neither the r one nor the r two allele says make pink flower. They both they either say make red flower or make white flower. But with incomplete dominance, we get neither red flower nor white flowers. Instead, we get an intermediate blend of pink flowers. And that is the pattern of inheritance that's referred to as incomplete dominance characterized by a blended phenotype that is an intermediate of phenotypes. And so this year concludes our introduction to incomplete dominance, and we'll be able to compare this to codominance in our next video. So I'll see you all there.
2
concept
Codominance
Video duration:
2m
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Video transcript
In this video, we're going to introduce codominance. And so codominance is a pattern of inheritance where heterozygotes with 2 different alleles equally express both phenotypes from each allele in patches. And so in other words, codominance is when 2 different alleles dominate together. And really when you take a look at the word codominance, the root co in front of co dominance is a root that means together, just like cooperate has the root co which means together. And so co dominance means that they're going to dominate together. Where one allele does not mask the expression of the other allele. Instead, they dominate together. And so we're gonna take a look at an example of codominance in red and white flowers. And so it's very very similar to our last example in our last lesson video, except instead of showing an incomplete dominance pattern of inheritance, here we're showing a codominance pattern of inheritance. And so once again, we're taking a look at these 2 different alleles, the r one allele, which, is gonna be associated with a red flower phenotype, and the r two allele, which is associated with a white flower phenotype. Now, when we cross a homozygous red flower with 2 r one alleles and a homozygous white flower with 2 r two alleles, we're going to get this Punnett square that we see here where we get, r one and r two heterozygotes as the offspring, just like what we saw in our last lesson video. But the difference was that with incomplete dominance in our last lesson video, the heterozygotes would create some kind of blended intermediate phenotype, that did not really exist in either of the parents. However, here with codominance, there's no blended intermediate phenotype. There's no pink flowers. Instead, with codominance, both phenotypes are going to be equally expressed. So you see patches of white flower down below and you also see patches of red flower. And so the white and, red, portions of this flower are expressed equally in patches, and that is what codominance is all about. And this is in heterozygotes that have 1 r one and 1 r two allele. And so hopefully this here helps you, better distinguish between incomplete dominance and codominance. But in our next lesson video, we're going to introduce one of the most common examples of codominance, which is blood type. So I'll see you all in that video.
3
Problem
Problem
You cross two true breeding lines of petunia. One produces red flowers and the other white flowers. The F1
offspring all show pink flowers. You conclude from this that:
A
Red is dominant.
B
White is dominant.
C
Red is incompletely dominant.
D
Red is incompletely recessive.
E
None of the answers listed above are correct.
4
concept
Codominance & Blood Type
Video duration:
5m
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Video transcript
In this video, we're going to talk about codominance as it relates to human blood type. And so it turns out that blood type in humans is a common and classic example of codominance. And so, of course, we introduced codominance in our last lesson video. Now, blood type in humans is determined by combinations of 3 possible alleles, which are capital I a, capital I b, or lowercase I. And so all combinations of these 3 alleles are possible for the genotype. Now the capital IA and capital IB alleles are actually the ones that are co dominant to each other. And that means that the capital I, a, does not dominate over the capital I, b, and and the capital I b does not dominate over the capital I a. So they do not mask each other. And, instead, they're going to both be equally expressed in patches whenever you have a heterozygote with both of these alleles. However, the lowercase I allele is recessive to the other 2 alleles, capital IA and capital IB. And so if we take a look at our example down below at the ABO blood types, notice that we have this chart here with 3 columns. The first column represents the genotype. The second column represents the surface molecules that are found on the red blood cells themselves. And the 3rd and final column represents the final phenotype or the blood type that the individual would actually have. And so notice that here in the first row of the genotype, what we have is capital I a, capital I a. So 2 alleles for capital I a. Or we have 1 capital I a and one lowercase I. And again, recall that the lowercase I is recessive to the capital I a, which means that only capital I a would be expressed. And so, either of these genotypes, either this one or this one, would lead to only a molecules on the surface of the red blood cell, Kind of like what you see over here. A red blood cell right here, surrounded by these a, molecules on the surface. And that, of course, would mean that this person would be a Type A blood. Now, the next row, what we have is capital I, B, capital I, B, or capital I, B, lowercase I. Again, the lowercase I is recessive to the capital IB, so only the capital IB is going to be expressed here in this genotype. But both of these genotypes here would lead to only B molecules on the surface of the red blood cell. So it would look like this red blood cell here with these B molecules on the surface. And of course, that would mean that this individual would have type b blood. Now when an individual has 1 capital I a and one capital I b together, these two alleles are co dominant to each other. And so that means that neither of them are going to dominate or mask the other. Instead, they are both going to dominate together. And they're both gonna be equally expressed. And so in that case, you get both a and b molecules equally expressed in patches on the surface of the red blood cell. And so again, here we have the red blood cell, but notice that we have patches of a and b on the surface of this red blood cell in these patches. And, neither of them dominate over the other, instead they are both equally being expressed on the surface. And that is a classic example of codominance. And so, of course, this person here would have a blood type of AB. They would have AB blood. And then last but not least, the final genotype is having 2 lowercase i's. And an individual that has 2 lowercase i's is not going to have either, molecule a or molecule b on the surface. And so instead, they're going to basically have, a red blood cell that has, you know, neither A or B blood. And so, instead, they're going to have type o blood. You can think that the, the o is almost like the naked, look here of the type o, blood without any surface molecules on its surface. And so this here concludes our introduction to codominance and blood type. And we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
5
Problem
Problem
If you look at a blood sample from a person who is heterozygous at the sickle cell locus you will see both normal circular red blood cells and sickle-shaped red blood cells. This is an example of
A
multi-locus inheritance.
B
complete dominance.
C
incomplete dominance.
D
codominance.
E
linked genes.
6
Problem
Problem
A gene for the MN blood group has codominant alleles M and N. If both children in a family are of blood type M, which of the following situations is possible?
A
Each parent is either M or MN.
B
Each parent must be type M.
C
Both children are heterozygous for this gene.
D
Neither parent can have the N allele.
7
Problem
Problem
The number of different alleles for ABO blood types is _____ resulting in _____ different blood types.