Sickle cell anemia is:
Correct answer: B. Caused by a change in a single base pair of DNA.
- A. Caused by substitution of valine by glutamic acid in the beta globin chain of haemoglobin.
- B. Caused by a change in a single base pair of DNA.
- C. Characterized by elongated sickle-like RBCs with a nucleus.
- D. An autosomal linked dominant trait.
Explanation
Sickle-cell anemia is a genetic disorder affecting the structure of hemoglobin, leading to sickle-shaped red blood cells. It is caused by a substitution mutation in the DNA sequence of the beta-globin gene, where a single nucleotide change (A to T) results in the replacement of glutamic acid with valine at the sixth position of the beta-globin chain. This change causes hemoglobin molecules to stick together under low oxygen conditions, deforming red blood cells into a sickle shape. Option B is correct because it directly describes the genetic mutation responsible for the disease. Option A is incorrect because it reverses the substitution of amino acids. Option C is wrong as mature red blood cells do not have a nucleus. Option D is also incorrect because sickle-cell anemia is autosomal recessive, not dominant.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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