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प्रश्न
It is said, that the harmful alleles get eliminated from population over a period of time, yet sickle cell anaemia is persisting in human population. Why?
उत्तर
Sickle-cell anaemia still persists in the population despite being harmful because this mutation can also be beneficial in certain conditions.
The mutant Hb5 type haemoglobin is found at high frequencies (up to 20% and above) in the tropical Africa.
It is known that heterozygotes (Hbs/HbA), having both types of haemoglobin show resistance to malarial infection because the body targets the Plasmodium falciparum-infected cell for destruction. In contrast, individuals homozygous for normal haemoglobin (HbA/HbA) suffer high mortality rates in early childhood due to malarial infection.
Thus, the allele for sickle cells has been maintained because heterozygotes have a higher reproductive success than either of the two possible homozygotes.
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संबंधित प्रश्न
A child suffering from Thalassemia is born to a normal couple. But the mother is being blamed by the family for delivering a sick baby.
(a) What is Thalassemia?
(b) How would you counsel the family not to blame the mother for delivering a child suffering from this disease? Explain.
(c) List the values your counselling can propagate in the families.
Identify 'a', 'b', 'c',’d’, 'e' and 'f' in the table given below:
| No. | Syndrome | Cause | Characteristics of affected individuals | Sex Male/Female/Both |
| 1. | Down's | Trisomy of 21 | 'a' (i) (ii) |
'b' |
| 2. | 'c' | XXY | Overall masculine development. |
'd' |
| 3. | Turner's | 45 with XO | 'e' (i) (ii) |
'f' |
Give reasons for the development of Turner’s syndrome and also mention its symptoms.
Which of the following characteristics are observed in a person suffering from Turner syndrome?
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 |
Thalassemia and sickle cell anaemia are caused due to a problem in globin molecule synthesis. Identify the correct statement from the following.
If a colour-blind man marries a woman who is homozygous for normal colour vision, the probability of their son being colour-blind is ______.
It is well known that Queen Victoria of England was a carrier for haemophilia. Since this is an X-linked disease, it can be predicted that ______.
Where are the genes for cytoplasmic male sterility in plants located?
“Genes contain the information that is required to express a particular trait.” Explain.
