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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
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 the importance of heterocyst in cyanobateria.
Name a disorder a human suffers from as a result of the monosomy of the sex chromosome. Give the karyotype and write the symptoms.
Give an account of one Mendelian and one chromosomal disorder you have studied.
HbA and HbS alleles of normal and sickle celled RBC are ______.
If a colour-blind man marries a woman who is homozygous for normal colour vision, the probability of their son being colour-blind is ______.
The most striking example of point mutation is found in a disease called ______.
A person with 47 chromosomes due to an additional Y-chromosome suffers from a condition called ______.
Read the following and answer from given below:
Turner's syndrome is an example of monosomy. It is formed by the union of an allosome-free egg and a normal 'X' containing sperm or a normal egg and an allosome-free sperm. The individual has 2n = 45 chromosomes (44 + X0) instead of 46. Such individuals are sterile females who have rudimentary ovaries, underdeveloped breasts, small uterus, short stature, webbed neck, and abnormal intelligence. They may not menstruate or ovulate. This disorder can be treated by giving female sex hormones to women from the age of puberty to make them develop breasts and have menstruation. This makes them feel more normal.
The number of Barr bodies present in a female with Turner's syndrome is ______
Why is thalassemia cotegorised as a Mendelian disorder? Write the symptoms and explain the causes of the disease. How does it differ from Sickle cell anaemia?
