Sickle-Cell Anaemia Inheritance Pattern — NEET Biology
✅ Asked in NEET 2026Which disorder is caused by substitution of Glutamic acid by Valine at the sixth position of the beta globin chain of haemoglobin?
Which disorder is caused by substitution of Glutamic acid by Valine at the sixth position of the beta globin chain of haemoglobin?
In a cross between a male and female, both heterozygous for the sickle cell anaemia gene, what percentage of the progeny will be diseased? (NEET 2021)
Select the correctly matched pair: (NEET 2020)
Answer & NCERT explanation
Correct answer: B — Sickle-cell anaemia
Sickle-cell anaemia is an autosomal recessive disorder caused by substitution of Glu by Val at the 6th position of the beta-globin chain (point mutation GAG -> GUG).
Read more NCERT concept on the PYQ
Sickle-cell anaemia: This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). The disease is controlled by a single pair of allele, HbA and HbS. Out of the three possible genotypes only homozygous individuals for HbS (HbSHbS) show the diseased phenotype. Heterozygous (HbAHbS) individuals appear apparently unaffected but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny, thus exhibiting sickle-cell trait. The defect is caused by the substitution of Glutamic acid
NTA tests whether students understand that only homozygous (HbSHbS) individuals show sickle-cell disease, while heterozygous (HbAHbS) carriers appear normal but can transmit the mutant gene. The common mistake is assuming heterozygous individuals show the disease phenotype or that they have a 50% chance of getting sick themselves—they don't. What to remember: Sickle-cell is autosomal recessive, so you need two copies of HbS allele to express the disease. Heterozygous carriers have a 50% probability of passing the HbS allele to offspring, not developing symptoms. This distinction between genotype and phenotype in recessive disorders is repeatedly tested across NEET exams.
What does NCERT say about Sickle-cell anaemia This autosome?
Has this concept appeared in NEET?
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