The pedigree in the figure below illustrates the inheritance of a sex-linked recessive trait. What is the genotype of individual II-5?

a. XHXH; b. XHXh; c. XhXh; d. XHY; e. XhY

Video transcript

Welcome back. Let's look at our next question. It says determine the genotype of Roman numeral 3- in the given pedigree that illustrates the inheritance of Red Green colour blindness. While we have a pedigree here with three generations labeled roman numerals 12 and three. The individuals in each generation labeled with Arabic numerals. So Roman rural 3-4 means we go to the third generation and look for individual number four. So we'll circle that person. This person is indicated with a square that square shape indicates a male and a genetic pedigree circle being female. And this shape is shaded in which indicates the individual is affected by the trait that we're looking at. So this is a color blind male. So that's the phenotype of our individual. But we're looking for the genotype since we're looking at the inheritance of red green color blindness. That's one of the more famous excellent traits the gene for color blindness inherited on the X. Chromosome. And that gene for color blindness is recessive. So we'll go ahead and indicate big C. Meaning normal vision since the gene for normal vision is dominant and a little C. Meaning colorblind. That's the recessive gene. So let's look at our possibilities for genotype and females who have two X chromosomes. They could be homos I guess dominant X. Big C. Big C. They would have normal vision. Then they could be a hetero ex Big C. X. Little C. This will be a female with normal vision but it will be a carrier. They have she has one copy of the gene for color blindness and one of her X chromosomes. And then she could also be homogeneous recessive. X. Little C. Little C. And she would be color blind. However, males only have one copy of X chromosome. So the male could be X. Big C. Y. And he'll have normal vision. Or it could be X. Little see why. And even though the gene for color blindness is recessive, he only has one copy. So he will be color blind. There's no possibility of being a mail carrier with an excellent trait. So our individual we know is a color blind male. So we automatically know there's only one possibility for his genotype and that is X. Little C. Y. When we look at our answer choices, choice A. Is X. Little C. Y. When we look at the other choices, we can see why they'd be wrong. Choice C. And choice D. Both involve females because there's two X chromosomes and choice B. Is X. Big C. Y. Which as we can see is the normal vision male. Since he has that dominant gene for normal vision and only one copy. So we can eliminate choice B. And so we have choice A. And we see that when we look back at our pedigree, that gene for color blindness came from that first generation one, the father in that generation who was color blind, um he would pass on to his son only a Y chromosome. So we don't have inheritance from him in the second generation. His son will inherit why from his father. And since his son we can see is not color blind. He inherited a normalcy from his mother. The mother in generation one could be a carrier. We know she's not colorblind. Um, we don't know anything about that until we see if she had a color blind son. We know she was a carrier, but she does not, none of her Children were color blind. So we see next, there's a daughter who's the mother of our individual. And because she's the mother of a color blind son, we know that she must have one gene for color blindness presumably, we know must have been inherited from her father because her father can only pass on, he has only one X. It is little C. And he will pass on that X. Little C. To all of his daughters. So both of his daughters are carriers for the gene for color blindness. They inherit another X from their mother. And in the case of both of them, we know that this must be big C. Because they are not colored by themselves. They are carriers for the gene. And in the third generation we have the sun with normal vision. His two Children with normal vision, their mother, his wife could be a carrier. But uh, we don't know unless she had a color blind child. Now the individual were interested in And his family's individuals 3 4 and five we see a color blind son. He inherited that gene from his mother, X. Little C. Y. two daughters who have normal vision. So we know they inherited at least one big C. But we don't know about their other gene because their father is not colorblind. We know his genome must be ex. Big C. Y. And they could have inherited either their mother's gene for color blindness and be carriers or their mother's normal gene and have the homos, I guess dominant. So just a little further exploration on this pedigree here, hope to see you in the next video.