Sickle cell anemia is a genetic disease, where hemoglobin gene is mutated. Hemoglobin gene is present in 11th chromosome (autosome). In the image explained by @shalinisharma98 the Mother and Father both are heterozygous carriers having one mutated sickle cell hemoglobin gene.
One of the offspring will be homozygous with mutated sickle cell genes. When both the chromosomes have mutated sickle cell hemoglobin gene they will be expressing sickle cell anemia disease. But when they have only one chromosome with sickle cell hemoglobin gene it will be carrier without having sickle cell anemia disease.
Sickle cell anemia trait is also resistant to malaria, hence a mutated gene also gets selected for better in other conditions.
The discussion helps understand how variations take place and how they are inherited to give rise to variety of phenotypes.
With this example of sickle cell anemia we can understand how variations may have come also in Darwin’s finches example and also in Pagalapos soil nematodes.
The discussion helped to understand how to represent genetic inheritance also clearing several confusions about representing patterns of inheritance.