{"id":1361,"date":"2020-08-06T22:28:52","date_gmt":"2020-08-06T22:28:52","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/theory-questions-and-answers\/theory-questions-and-answers-iv\/"},"modified":"2020-08-06T23:48:42","modified_gmt":"2020-08-06T23:48:42","slug":"theory-questions-and-answers-iv","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/theory-questions-and-answers\/theory-questions-and-answers-iv\/","title":{"rendered":"Theory Questions and Answers IV"},"content":{"rendered":"\n

Questions<\/h3>\n<\/span>\n\n\n

Scroll down for answers!<\/em><\/p>\n\n\n\n

  1. A woman with blood group O and a man with blood group AB have a child with blood group AB. Explain how this is possible.<\/li>
  2. When does an allele become polymorphic?<\/li>
  3. What are multifactorial traits?<\/li>
  4. What causes phenotypic variations?<\/li>
  5. How are thymine dimers formed in DNA and which mechanism is responsible for the repair? Name a disease that is caused by the failure of this repair system.<\/li>
  6. Is it possible for a healthy couple to have two sons: one with colour blindness and haemophilia and the other with just haemophilia? If yes, explain.<\/li>
  7. What is the difference between Pleiotropy and Genetic heterogeneity? Give examples of genes that exhibit both phenomena. <\/li>
  8. Explain the difference between enzyme replacement therapy and protein augmentation therapy with examples.<\/li>
  9. Explain Loss of Heterozygosity. What is its significance in oncogenetics?<\/li>
  10. What is the phenotype of parents with IA<\/sup>iHh and iihh? What would be the phenotype of their children?  <\/li><\/ol>\n\n\n<\/span>\n

    Answers<\/h3>\n<\/span>\n\n\n
    1. Normally, each parent gives one chromosome(containing one copy of the gene) to the child. In this case, it is possible that the father has both genes(IA<\/sup> and IB<\/sup>) on the same chromosome(due to unequal cross over) so when he donated that chromosome to his child, the child inherited both genes as well. The mother will donate one chromosome with the ‘i’ gene but since this is recessive, the co-dominant AB will be expressed instead.<\/li>
    2.  An allele is regarded as polymorphic if it is found in more than 1% but less than 100% of the population. Alleles that are found in less than 1% of the people are known as rare variants.<\/li>
    3. Multifactorial traits are those that are influenced by the interaction of various genes with the environment.<\/li>
    4. Phenotypically variant traits such as height, weight, hair colour, eye colour, etc are multifactorial traits i.e the variation is caused mainly by the difference in environments and by the action of various genes.<\/li>
    5. Thymine dimers are formed when the DNA is exposed to Ultraviolet(UV) rays and it is repaired by Nucleotide Excision Repair. Failure of this repair system leads to Xeroderma Pigmentosum; a cancer syndrome.<\/li>
    6. Yes, it is possible. Both colour blindness and haemophilia are X-linked recessive traits. This means that the father has genotype XHC<\/sup>Y(because he is healthy) and the mother has XHc<\/sup>XhC<\/sup>(because she is also healthy). The first son has Xhc<\/sup>Y and the other has XhC<\/sup>Y. The mother made recombinant genes XHC<\/sup> and Xhc<\/sup>.<\/li>
    7. Pleiotropy is when one gene controls many, unrelated phenotypic traits. For example, the mutation that causes Phenylketonuria affects skin and hair colour and also leads to mental retardation while Genetic Heterogeneity is when multiple genes control the same phenotypic trait. It is seen in Alzheimer’s disease.<\/li>
    8. Enzyme Replacement Therapy, as the name implies, is when the missing enzyme is introduced into the cells. It is used for intracellular enzyme defects e.g to supplement missing enzymes in lysosomal storage diseases while Protein Augumentaion Therapy is used to supplement missing proteins that are present in the blood or extracellular space e.g to supplement clotting factors in haemophilia. They are both traditional therapies.<\/li>
    9. Loss of Heterozygosity is when a heterozygous individual loses one of his\/her chromosomes due to epigenetic silencing, mutations, somatic recombination and loss of chromosome. The loss of the wild type allele\/chromosome will cause the recessive trait to be expressed. It is frequently seen in inherited forms of Retinoblastoma and breast cancer where the heterozygous individuals lose the wild type chromosome of the tumour suppressor gene, thereby causing the mutated one to be expressed i.e it will not function. This is why inherited cases of cancer have an earlier age of onset than the sporadic ones.<\/li>
    10. The phenotype for IA<\/sup>iHh is blood group A and the phenotype for iihh is the Bombay blood group. To get the phenotype of the children, we have to make a cross.<\/li><\/ol>\n\n\n\n

      Parental phenotype:               Blood group A \u00d7 Bombay Blood group<\/p>\n\n\n\n

      Parental genotype:                  IA<\/sup>iHh \u00d7 iihh<\/p>\n\n\n\n

      Gametes: (IA<\/sup>H)(IA<\/sup>h)(iH)(ih) \u00d7 (ih)       *we write only one gamete for the second parent because this is the only type that is produced<\/p>\n\n\n\n

       <\/td>(ih)<\/td><\/tr>
      (IA<\/sup>H)<\/td>IA<\/sup>iHh<\/td><\/tr>
      (IA<\/sup>h)<\/td>IA<\/sup>ihh<\/td><\/tr>
      (iH)<\/td>iiHh<\/td><\/tr>
      (ih)<\/td>iihh<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

      F1 phenotype: Blood Group A: Blood Group O: Bombay Blood group<\/p>\n\n\n\n

      F1 phenotypic ratio: 1:1:2<\/p>\n<\/span>

      Questions<\/h3>

      Answers<\/h3><\/div>","protected":false},"excerpt":{"rendered":"

      Questions Scroll down for answers! A woman with blood group O and a man with blood group AB have a child with blood group AB. Explain how this is possible. When does an allele become polymorphic? What are multifactorial traits? What causes phenotypic variations? How are thymine dimers formed in DNA and which mechanism is […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1357,"menu_order":3,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1361","page","type-page","status-publish","hentry"],"yoast_head":"\nTheory Questions and Answers IV – Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/theory-questions-and-answers\/theory-questions-and-answers-iv\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" 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