Sickle cell anaemia has not been eliminated from the African population because

In certain plant species,red flower colour is incompletely dominant to white flower colour (the heterozygote is pink) and tall stems are completely dominant to dwarf stems. If a tall pink plant $(TtRr)$ is crossed with a tall white plant $(TTrr),$ which one of the following types of plants would be produced in the offspring?

Which of the following statements are false?
$I.$ $A$ dominant allele determines the phenotype when paired with a recessive allele.
$II.$ $A$ recessive allele is weaker than a dominant allele.
$III.$ $A$ recessive allele does not show its effects when paired with a dominant allele.
$IV.$ $A$ dominant allele is always better for an organism.

What is $HbA_2$ composed of?

Identify the correct and incorrect statements from the following:
$(1)$ Mendel is considered the father of modern genetics.
$(2)$ Down's syndrome is a sex-linked chromosomal disorder.
$(3)$ Sickle cell anemia is an example of point mutation.
$(4)$ Color blindness is a hereditary trait.
$(5)$ Triploid female flies are found in Drosophila.

$A$ : Test cross is the tool for knowing linkage between genes.
$R$ : Monohybrid test cross gives two phenotypes and two genotypes.