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Question
Represented below is the inheritance pattern of a certain type of traits in humans. Which one of the following conditions could be an example of this pattern?
Represented below is the inheritance pattern of a certain type of traits in humans. Which one of the following conditions could be an example of this pattern?
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Solution
The correct option is C Haemophilia
The pattern shows that the trait is inherited from mother to son and from father to daughter. As we know that human male has XY sex chromosomes and human females have XX sex chromosomes. A son always inherits the X-chromosome from mother and Y-chromosome from father while a father always passes its X-chromosome to his daughters. A X-linked trait is always passed from mother to son and from father to daughter; hence the pattern shows inheritance of X-linked trait. If it would have been an autosomal trait, irrespective of the sex of child, both parents would have passed it to all the progeny with equal probability. Phenylketonuria is an inborn error of metabolism and is caused by mutation in PAH gene, present on chromosome 12. It is inherited in an autosomal recessive manner and hence does not follow the shown pattern. Sickle-cell anemia is caused by point mutation in gene for β-globin chains (Hbb) of hemoglobin, present on chromosome 11. It is also inherited in an autosomal recessive manner and hence does not follow the shown pattern. Thalassemia are a group of blood disorders which are caused by mutations in the HbB and HbA genes present on chromosome 11 and chromosome 16 respectively. Thus, they are inherited in an autosomal recessive manner. Haemophilia is a sex-linked disorder because the governing genes are present of X-chromosome which is a sex chromosome in human. The trait is transmitted to offspring in a sex-linked manner. Hence, the pattern is showing the inheritance of a sex-linked recessive disorder like haemophilia. Correct option is C.
The pattern shows that the trait is inherited from mother to son and from father to daughter. As we know that human male has XY sex chromosomes and human females have XX sex chromosomes. A son always inherits the X-chromosome from mother and Y-chromosome from father while a father always passes its X-chromosome to his daughters. A X-linked trait is always passed from mother to son and from father to daughter; hence the pattern shows inheritance of X-linked trait. If it would have been an autosomal trait, irrespective of the sex of child, both parents would have passed it to all the progeny with equal probability. Phenylketonuria is an inborn error of metabolism and is caused by mutation in PAH gene, present on chromosome 12. It is inherited in an autosomal recessive manner and hence does not follow the shown pattern. Sickle-cell anemia is caused by point mutation in gene for β-globin chains (Hbb) of hemoglobin, present on chromosome 11. It is also inherited in an autosomal recessive manner and hence does not follow the shown pattern. Thalassemia are a group of blood disorders which are caused by mutations in the HbB and HbA genes present on chromosome 11 and chromosome 16 respectively. Thus, they are inherited in an autosomal recessive manner. Haemophilia is a sex-linked disorder because the governing genes are present of X-chromosome which is a sex chromosome in human. The trait is transmitted to offspring in a sex-linked manner. Hence, the pattern is showing the inheritance of a sex-linked recessive disorder like haemophilia. Correct option is C.
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