Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation. According to Figure 1, which of the following assumptions about the P1 generation must be true?
Answer(s): A
This question asks you to conclude something about the P1, or parental, generation. The easiest way to do this is to go through each statement and analyze it. Choice A states that Albert did not have the gene for hemophiliA. If we look at the pedigree, we see that this in fact is true; he doesn't have the gene as indicated by his unshaded square. If he did have the gene then he would have been a hemophiliac, since the gene is X- linked. So choice A is the correct answer. But let's just take a look at the other choices to be sure. Choice B states that Queen Victoria had two X chromosomes, each with the hemophilia gene. Now it's true that Queen Victoria had two X chromosomes all normal females do. However, as indicated by the half shading on her circle in the pedigree, she was a carrier of the gene for hemophilia; that is, she only had one copy of the gene.So choice B is wrong. Choice C states that neither Albert nor Victoria had the gene for hemophiliA. Well, Victoria was a carrier, so choice C is wrong too. Choice D states that Albert was a carrier. First of all, men cannot be carriers of an X-linked trait. If they have a copy of the gene in question, then they express the trait.Males cannot have two copies of a X-linked trait because they have only one X chromosome. So, choice D is also wrong.
Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation.Which of the following best explains why Louis IV was NOT a hemophiliac?
Answer(s): B
A male can inherit an X-linked trait only from his mother, since he inherits his one X chromosome from her.Thus, Louis IV, who was normal, did not inherit the gene for hemophilia from his mother, who is not shown on the pedigree. Remember, Louis IV was not a blood relative of the Queen, he was her son-in-law. Choice A is incorrect, since Louis IV's son, Frederick, has hemophilia because he inherited the gene from his mother, who was a carrier (although we don't know her name). Besides, whether Louis IV's children were hemophiliacs, carriers, or normal, is irrelevant to the discussion of why Louis himself was normal. Choice C is incorrect because Albert was not a blood relative of Louis IV, so Albert's genotype is independent of Louis' genotype. As for choice D, while it is true that only females can be carriers of the hemophilia gene, or of any X-linked gene for that matter, this does not answer the question.
Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation. If Beatrice had married a hemophiliac and had a son, what is the probability that the son would have been a hemophiliac?
Answer(s): C
If you look at the pedigree, you'll see that Beatrice, a member of the F1 generation, was a carrier of the gene for hemophilia, which means that she had one copy of it on one of her X chromosomes. In reality, Beatrice married a normal male, whose name you're not given; but for the purpose of this question, you're asked to determine the probability that any of her sons would have been hemophiliacs if she had in fact married a hemophiliac. So this is basically a cross between a carrier and a hemophiliac. Therefore, Beatrice's genotype is XhX, and her theoretical husband's genotype is XhY. So, in a cross between these two people, 50% of all their children are expected to be hemophiliacs. But you need to look at the disease in terms of gender; 50% of the daughters are expected to be hemophiliacs; the other 50% will be normal. Likewise, 50% of the sons are expected to be hemophiliacs; the other 50% to be normal.
Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation. Theoretically, what percentage of Victoria Eugenia's sons should have been hemophiliacs?
If you look at the pedigree, you'll see that Victoria Eugenia had four sons, three of which were hemophiliacs.So, 75% of her sons turned out to be hemophiliacs. You know that these sons inherited the disease from their mother, as opposed to their father, Alfonso III of Spain, because their mother was a carrier of the disease, as can be seen on the pedigree, and their father was normal. Okay, so 75% was the actual percent, but the question asks you to determine the theoretical probability that Victoria Eugenia's sons would be hemophiliacs.So, what you have to do is just work out the cross between a carrier female and a normal male and look at the results. And, if you do that, you'll find that theoretically, 50% of Victoria Eugenia's daughters should have been carriers, 50% should have been normal; and 50% of her sons should have been hemophiliacs, 50% should have been normal. So the probability that Victoria Eugenia's sons would have been hemophiliacs is 50%.
Hemophilia is a genetically inherited disease that causes the synthesis of an abnormal clotting factor. As a result, hemophiliacs bleed excessively from the slightest injury. The figure below is a partial pedigree for the hemophilia trait in Queen Victoria's descendants. The pedigree indicates no history of hemophilia for either parent prior to the F1 generation.Based on the pedigree, what is the most reasonable explanation for Rupert's hemophilia?
Answer(s): D
According to the pedigree, Rupert's father was normal, his mother, Alice was a carrier of the disease, his maternal grandmother was normal, and his maternal grandfather, Leopold, was a hemophiliac. Well, knowing this bit of family history allows us to reconstruct the transmission of the gene for hemophilia through these three generations, and also allows us to rule out choices B and C, since Alice was NOT a hemophiliac and her husband was normal. Okay, Leopold the hemophiliac necessarily passed on the hemophilia gene to his daughter Alice, since she inherited one of her X chromosomes from him. Alice's mother was normal, so Alice's other X chromosome was normal. Alice married a normal man, and gave birth to three children, a normal daughter and son, and a hemophiliac son, Rupert. Now, the reason why Rupert had hemophilia was because he inherited the X chromosome with the hemophilia gene on it from his mother, who in turn, inherited it from her father. So rupert's hemophilia is a direct result of his maternal grandfather's hemophilia, and therefore choice D is the right answer. Choice A is wrong because a mutation of the Y chromosome that Rupert inherited from his father would not affect Rupert's inheritance of hemophilia, since the gene for hemophilia is located on the X chromosome, not the Y.
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