Read the passage below to answer the question: Haemophilia is a disorder in which blood fails to clot. Saad, a male haemophiliac, marries Sara, a normal woman and together they have four children, two boys (Ahmed and Ali) and two girls (Alia and Ayesha). None of the children displays the symptoms of Haemophilia. Ahmed, Ali, Ayesha, and Ali all marry normal individuals and have children. None of Ahmed's or Ali's children, male or female, display symptoms of haemophilia, but the sons of Alia and Ayesha display symptoms of haemophilia while the daughters of Alia and Ayesha do not. Which of the following best explains the reason that Ahmed, Ali, Ayesha and Alia do not display symptoms of haemophilia, even though their father, Saad, is a haemophiliac?
Correct answer: B. Haemophilia is an X-linked disorder, and even though Alia and Ayesha received a hemophiliac X-chromosome from Saad, Sara gave them a normal X-chromosome
- A. Haemophilia is an X-linked disorder, and Saad can only pass on his Y chromosome
- B. Haemophilia is an X-linked disorder, and even though Alia and Ayesha received a hemophiliac X-chromosome from Saad, Sara gave them a normal X-chromosome
- C. Haemophilia is a Y-linked disorder, and therefore cannot be displayed in females
- D. Haemophilia is a Y-linked disorder ,and Ahmed and Ali must have received an X Chromosome from Saad
- E. Haemophilia is an X-linked disorder, and even though Ahmed and All received a Hemophilia X chromosome from Saad, Sara gave them a normal X chromosome
Explanation
Haemophilia is an X-linked chromosome, not a Y-linked chromosome. Daughters of Sara and Saad, Alia and Ayesha receive an X chromosome from both of their parents. Even though hemophilia X-chromosome is received by these daughters from Saad they received normal X from their mother, because of which they do not show any symptoms. Option A is wrong because Saad can pass X as well as Y chromosomes to his offspring. Options C and D are wrong because it is not a Y-linked but an X-linked disease. Option E is wrong because Ahmed and Ali can not receive an X chromosome from Saad (their father), they should receive a Y chromosome, for them to be male.
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About Inheritance
Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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