Question 7. Ten years from of members of a small family. The results don\'t fit
ID: 147422 • Letter: Q
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Question 7. Ten years from of members of a small family. The results don't fit the scheme shown above. You suddenly remember the "Bombay phenotype" that you learnt as an undergraduate in a genetics course. Which of the following blood groups in parents and children represents a case of the Bombay phenotype? (a) Parents: Type A and AB: Child is O (b) Parents: Type A and AB: Child isA (c) Parents: Type A and AB: Child is B (d) Parents: Type A and AB: Child is AB (e) Parents: Type A and AB: Child is A, AB or O (f) Parents: Type O and O: Child iso now, you are a doctor in New York City. Your assistant has typed the blood uestfion Š. Gene duplication is an important evolutionary mechanism by which a species has two or more nearly identical genes. (a) Suppose there are two genes, A and B, that specify the production of the same enzyme. An abnormal phenotype arises when the individual does not make any of that enzyme. What ratio of normal versus abnormal progeny would result from a dihybrid self cross, where A and B encode the functional enzyme and a and b do not? (b) Suppose now that there are three genes specifying production of this enzyme, and again that a single functional allele is sufficient for wild type phenotype. What ratio of normal versus abnormal progeny will result from a mating of triply heterozygous parents?Explanation / Answer
Q7)Ans is (f) Parents:type O and O:Child is O.
In human, blood group is determined by the presence of antigen A or B or by both or by absence of both antigens on RBCs membrane.The A and B antigens are formed from a precursor molecule ,called H substance(coded by H gene) which is found in every individual.The H substance contain three sugar molecules galactose,N-acetyl glucosamine and fucose.The enzyme Fucosyl transferase add the fucose to the terminal galactose residue.A dominant allele H at the H locus codes the enzyme but the recessive allele hh encodes a defective enzyme.
In case of A antigen,the H substance contain an additional N-acetyl galactoseamine added by N-acetyl galactosyl transferase.In B antigen the additional group in H substance is a galactose added by galactose transferase.Individuals of AB type possess both enzymes and thus have both A and B antigens whereas individuals of type O contain only H substance.
In Bombay Phenotyp ,the individuals have hh alleles coding defective enzyme fucosyl transferse which is unable to make H substance.As a result no A or B antigens are synthesized on RBC membrane.So they appear as blood type O.
Parents with blood type A and AB must have children with blood group A or B or AB.So their children will not be of O type.
Thus parents type O and O will produce children O type who will show Bombay phenotype.
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