What does the given symbol represent?

What are both Sickle-cell anemia and Huntington's chorea?

In sickle cell anemia -

Hereditary diseases constitute an important factor in checking the growth of population of a small community if:

$A$ normal-visioned man whose father was colourblind marries a normal woman whose father was also colourblind. They have one son. What is the probability of the son being colourblind (in $\%$)?

If both parents are carriers for thalassaemia,which is an autosomal recessive disorder,what are the chances of pregnancy resulting in an affected child?