The A and B antigens in humans may be found in water-soluble form...

Question

The A and B antigens in humans may be found in water-soluble form in secretions, including saliva, of some individuals (Se/Se and Se/se) but not in others (se/se). The population thus contains 'secretors' and 'nonsecretors.'

Determine the proportion of various phenotypes (blood type and ability to secrete) in matings between individuals that are blood type AB and type O, both of whom are Se/se.

Accepted Answer

Hi, I'm Raman. Welcome back. Let's look at our next problem. It says fut one gene encodes the antigens found on the surface of red blood cells. While fut two encodes those found on mucosal tissue and saliva cells. Individuals who have mutations in both alleles of the fut two gene are non secretor, determine the percentage of secretor when a heterozygous secretor female with type O blood group marries a nonsecretor male with type O blood group. So this question gives us a lot of information, some of which is extraneous to the question we're trying to answer. So it's helpful in a question like this to zoom in on what it's asking for. So our question is asking for um the in the offspring of a specific cross, what percent are secretor? So we're only talking about this sense of being a secretor and that only depends on this fut two jean. The blood type status is independent of secretor secretor status. So the two have no impact on each other. So the information that the parents are both type O, we don't need it to solve our problem. So let's focus on this. Uh meaning of being a secretor. So it's saying that um if you have mutations in both of your, all of the fut two gene, you're a nonsecretor. So you don't. Uh the secretor are people who release uh blood group antigens into other bodily fluids. So you might find it in their saliva for instance, as well as in their blood. So let's see what, how we would uh figure this out. So let's call the gene for fut two secretor S and since it says you have to have mutations in both to be a nonsecretor, we'll call big S being a secretor as its dominant. Since you have to have two mutant alls and little s the mutant allele, we'll call it the ll for being a nonsecretor. So we know that our parents are heterozygous secretor female. So our mother here is heterozygous for being a secretor. So she's big s little s and the father is a nonsecretor. So male is little less, a little less. So we just put up our pan and square. So all we need is a simple square, four square puit square here. We've got our hetero, I get mother here and homozygous recessive father and we just fill that in and we see that half of the offspring will be heterozygous. So they will be secretor since that's the dominant gene and half of them will be non secretor since they will have two mutant allys of the fut two gene. So what percent are secretor. 50% are secretor. Since that's the question that were being asked here. So look over our answer choices and that's choice c 50%. So again, this is a great example of a problem where we're given a lot of information that we don't need to answer the question they're asking, we don't need information about FU tt one gene. We don't need to know that the parents are type o blood group. We just need to know about their fut two gene and their secretor status. So again, the percentage of secretor when heterozygous secret or female typo blood group marries a nonsecretor male with type O blood group is choice c 50%. See you in the next video.

Key Concepts

Blood Type Genetics

Secretor Status

Punnett Square Analysis

Watch next