how incomplete penetrance, variable expressivity, pleiotropy, and genetic heterogeneity can affect the severity of a disease in a family

Penetrance is the proportion that indicates the carrier capacity of a particular variant by an
individual that is associated with the trait for expressing the phenotypic characters. This indicates
the chances of mutation that is due to expression of the clinical symptoms. Accordingly if there
is incomplete penetration then the gene will not get its capacity of expression. This may lead to
incomplete expression of the characters as well. It sometimes leads to the absence of the clinical
symptoms of the disease as a result the disease is not correctly diagnosed at the time ,if ever we
consider an autosomal dominant condition that shows incomplete penetrance this may induce the
mutation of breast cancer by leading to mutation in BRCA1 gene. This penetration property of
the gene signifies the expression of the phenotypic characters in gene expression. This also
determines the dominant and recessive characters of the gene according to their ways of function
and expression powers.
This property of the gene becomes difficult to associate itself with the gene function even in the
case of disease which are due to certain single polymorphic alleles. They relate to age, gender
and even the environmental factors. Even the codetermining factors like smoking, food habits etc
can have their impact on the gene function as well as penetration.
Hence from this penetration can be defined as if the probable aspect of expression of
a phenotypic character if the individual has inherited a predisposing genotype. But if the
probability is less than 1.0 then that genotype which is causing disease is...