One gene – one enzyme hypothesis was postulated by

  • R. Franklin

  • Hershey and Chase

  • A. Garrod

  • A. Garrod


D.

A. Garrod

'One gene - one enzyme' hypothesis was given by Beadle and Tatum (1948) which states that particular gene controls the synthesis of specific enzyme. Later, it was modified to 'one gene-one polypeptide hypothesis' by Yanofsky et.al. (1965).

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Test cross involves

  • crossing between two genotypes with recessive trait

  • crossing between two F1 hybrids

  • crossing the F1 hybrid with a double recessive genotype

  • crossing the F1 hybrid with a double recessive genotype


C.

crossing the F1 hybrid with a double recessive genotype

The test cross involves the crossing of F1 hybrid with a double recessive genotypic parent. By test cross, the heterozygocity and homozygocity of the organism can be tested.
Thus, the offspring will be 100% dominant, if the individual which crossed with recessive parent i.e., (tt) was homozygous dominant and ratio will be 50% dominant and 50% recessive if the individual was heterozygous dominant. In dihybrid test cross, ratio will be 1:1:1:1.

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Sickle cell anaemia has not been eliminated from the African population because

  • it is controlled by recessive genes

  • it is not a fatal disease

  • it provides immunity against malaria

  • it provides immunity against malaria


C.

it provides immunity against malaria

Sickle cell anaemia (in which RBCs become sickle shaped and stiff) is a genetic disorder that is autosomal and linked to a recessive allele. It has not been eliminated from the african population because it provides immunity against malaria. People who are heterozygous for sickle allele are much less susceptible for falciparum malaria which is one of the main causes of illness and death in them. Thus, the sickle cell allele is maintained at high levels in population where falciparum malaria is common. 

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Both sickle cell anaemia and Huntington's chorea are

  • bacteria-related diseases

  • congenital disorders

  • pollutant-induced disorders

  • pollutant-induced disorders


B.

congenital disorders

Both sickle cell anaemia and Huntington's chorea are congenital genetic disorders. Sickle cell anaemia was first opened by James Herrick (1904). In this disease the patient's haemoglobin level reduced to half of the normal and the RBCs become sickle shaped. A single mutation in a gene can cause sickle cell anaemia.
Huntington's chorea is caused by autosomal mutation which is dominant. The gene is present on chromosome number 4.

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If a colourblind woman marries a normal visioned man, their sons will be

  • all normal visioned

  • one-half colourblind and one-half normal

  • three-fourths colourbling and one-fourth normal

  • three-fourths colourbling and one-fourth normal


D.

three-fourths colourbling and one-fourth normal

Colour blindness is a disease in which a person is unable to differentiate between red and green colour. The gene for this disease is located on the X-chromosome. So, if a carrier or colour blind woman marries a normal man, it will produce all the sons colour blind .

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