Part 1: Genes, Chromosomes, and Heredity
Extensions of Mendelian Genetics
of a gene are called
that occurs most frequently in nature is called the
(change in the DNA) that causes the reduction or loss of a wild-type function is called a loss of
mutation. If the loss is complete, the allele that results in a
Some loci exhibit
where neither allele is dominant.
Some genes exhibit
, where both alleles contribute to the phenotype of a
. An example is the
Some traits are controlled by
alleles. Examples include the human
A loss of
mutation may behave as a recessive
state, but exhibit a separate
in a heterozygote.
Genes present on the
exhibit unique patterns of inheritance due to the presence of only one X chromosome in
Some phenotypes are affected by sex
and can be either
if the phenotype is restricted to one sex, or
if restriction is not absolute.
Phenotypic expression may also be influenced by the
as well as by genotype and result in
of the genotype.
One component of the
, such as the position
Another component of the
and many phenotypes show temperature sensitivity.
In cases of
, phenotypic expression may depend on the
origin of the chromosome.
Oct 2, 2008