Why is sickle cell disease most common among people living in tropical regions, and their descendants?

Sickle cell disease is caused by a recessive allele of the haemoglobin gene. When two copies are present (i.e. it is homozygous), many red blood cells become sickle-shaped, leading to disease.

However, if only one copy of this allele is present (heterozygous, or "sickle cell trait"), the carrier does not display symptoms. Additionally, the single copy confers resistance to malaria - a disease most common in tropical regions (e.g. sub-Saharan Africa). So in these regions, people with sickle cell trait are more likely to survive and reproduce than those without. This amounts to a selective advantage for the sickle cell allele.

SG
Answered by Sean G. Biology tutor

17180 Views

See similar Biology A Level tutors

Related Biology A Level answers

All answers ▸

Explain the formation of an action potential.


Describe methods of solute transport across a cell membrane.


What's the mechanism behind inspiration in human?


Which of these DNA mutations is likely to have the greatest effect on the structure of the encoded protein? Justify your answer. •Single base substitution •15 bases base deletion •Insertion of 2 bases


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning