$A$ human male is heterozygous for autosomal genes $A$ and $B$ and is also hemizygous for the $hemophilia$ gene. What proportion of his sperm will be $abh$?

$A$ doctor's son:

Haemolytic jaundice is caused due to a dominant gene but only $10\%$ of the people who carry the gene actually develop the disease. $A$ heterozygous man marries a homozygous normal woman; what proportion of the children would be expected to develop the haemolytic disease?

Read the following statements carefully:
$(1)$ Ploidy is a structural chromosomal abnormality.
$(2)$ Hemophilia is an autosomal recessive disorder in which blood does not clot.
$(3)$ Recombination is one of the factors responsible for evolution.
$(4)$ Genetic mapping allows the determination of the specific location of a gene on a chromosome.
$(5)$ Snapdragon plant is an example of incomplete dominance.
$(6)$ $ABO$ blood grouping shows both dominance and codominance.
Identify the correct and incorrect statements from the given options.

Select the group of $CORRECT$ statements.
$I$. If phenotype of offsprings shows only the dominant trait then the parent plants are heterozygous.
$II$. $A$ true breeding line shows stable trait inheritance and expression for several generations.
$III$. In mendelian experiment material,contrasting characters can be easily recognized.
$IV$. When a single gene controls two (or more) different traits,it is called polygene.
$V$. When interactions occurs between the alleles of different genes present on the same or different chromosome it is called intragenic interaction.

It is said that harmful alleles are eliminated from a population over a period of time,yet sickle cell anaemia persists in the human population. Why?