A couple, both with sickle cell trait (heterozygous), are planning to have children. What is the probability their child will have sickle cell anaemia? Explain the higher prevalence of sickle cell tra

Sickle cell trait is more prevalent in tropical countries because it provides a significant survival advantage against malaria. Tropical regions often have a high incidence of malaria, a parasitic disease. Individuals who are heterozygous for the sickle cell gene (HS genotype) are resistant to malaria because the presence of some abnormal haemoglobin makes their red blood cells less suitable for the malaria parasite to complete its life cycle. This resistance means they are more likely to survive and reproduce in malaria-prone areas compared to individuals with normal haemoglobin (HH), who are susceptible to malaria, or individuals with sickle cell anaemia (SS), who suffer from a severe disease. This natural selection leads to a higher frequency of the sickle cell allele and thus the sickle cell trait in these populations.