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प्रश्न
Jacob is genetically a carrier of the disorder that affects the shape of the RBCs, as shown in the diagram below. His son James suffers from the same disorder.
- Give the biochemical reason for the disorder that changes the shape of the RBCs, as shown above.
- Draw a Punnett square to show the genotype of the mother of James.
- Name and define the type of 'point mutation' responsible for this disorder.
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उत्तर
- Red blood cells take on a sickle-like structure when oxygen tension is lowered since the deoxygenated sickle cell haemoglobin (HbS) molecules polymerize to form long fibres.
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Given Jacob is a carrier, his genotype has to be HbA HbS.
James, Jacob's child, suffers with the condition; so, his genotype is HbS HbS.
According to the provided data, James must inherit one HbS allele from each parent if he is to have sickle call anaemia (HbS HbS). Given Jacob's known carrier status (HbAHbS), he most certainly passed on the HbS gene to James. James's need for two HbS alleles requires the mother to have likewise supplied a HbS allele. The condition (HbS HbS) or a carrier (HbA HbS) can have an impact on the mother.
Case 1. When mother is a carrier (HbA HbS)
Mother
HbA HbS HbA
JacobHbA HbA
(Normal)HbA HbS
(Carrier)HbS HbA HbS
[Carrier]HbS HbS
[Sickle cell]James will suffer from a disorder.
Case 2. When mother is affected (HbS HbS)
Mother
HbS HbS HbA
JacobHbA HbS
(Carrier)HbA HbS
(Carrier)HbS HbS HbS
[Sickle cell]HbS HbS
[Sickle cell]James will suffer from a disorder.
- A monogenetic condition, sickle cell anaemia is caused by a single base-pair point mutation in the β globin gene, substituting glutamic acid for valine in the β-globin chain.
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संबंधित प्रश्न
A couple with normal vision bear a colour blind child. Work out a cross to show how it is possible and mention the sex of the affected child.
Attempt any TWO of the following:
‘The gene for sickle cell anaemia in homozygous condition is lethal and produces sickle cell trait in heterozygous carrier’. Explain.
Which of the following traits is never observed in a human female?
Name a disorder a human suffers from as a result of the monosomy of the sex chromosome. Give the karyotype and write the symptoms.
Match Column I with Column II and select the correct option:
| Column I | Column II | ||
| p. | Pleiotropy | I. | More than two alleles occur at the same locus on homologous chromosomes |
| q. | Multiple alleles | II. | Expression of both the alleles m heterozygous condition |
| r. | Polygenic | III. | Multiple effect of single gene |
| s. | Co-dominance | IV. | Single phenotypic character influenced by more than two genes |
The most striking example of point mutation is found in a disease called ______.
If both parents are carriers for thalassaemia, which is an autosomal recessive disorder, what are the chances of pregnancy resulting in an affected child?
Rajesh and Mahesh have defective haemoglobin due to genetic disorders. Rajesh has too few globin molecules while Mahesh has incorrectly functioning globin molecules. Identify the disorder they are suffering from.
| Rajesh | Mahesh | |
| A. | Sickle cell anaemia - an autosome linked recessive trait | Thalassemia - an autosome linked dominant trait |
| B. | Thalassemia - an autosome linked recessive blood disorder | Sickle cell anaemia - an autosome linked recessive trait |
| C. | Sickle cell anemia - an autosome linked recessive trait | Thalassemia - an autosome linked recessive blood disorder |
| D. | Thalassemia - an autosome linked recessive blood disorder | Sickle cell anaemia - an autosome linked dominant trait |
Why is the frequency of red-green colour blindness is many times higher in males than that in females?
Which of the following is an example of a Mendelian disorder?
