Bio3400
Chapter 4
Extensions of Mendelian Genetics
Alternative
forms
of a gene are called
; the
allele
that occurs most frequently in nature is called the
type.
A
(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
allele.
Some loci exhibit
dominance,
where neither allele is dominant.
Some genes exhibit
, where both alleles contribute to the phenotype of a
. An example is the
blood
group.
Some traits are controlled by
alleles. Examples include the human
blood
group
and the
locus
in
Drosophila
.
A loss of
mutation may behave as a recessive
allele
in the
homozygous
state, but exhibit a separate
phenotype
in a heterozygote.
Genes present on the
chromosome
exhibit unique patterns of inheritance due to the presence of only one X chromosome in
males.
Some phenotypes are affected by sex
and can be either
sex
-
if the phenotype is restricted to one sex, or
sex
-
if restriction is not absolute.
Phenotypic expression may also be influenced by the
as well as by genotype and result in
variation
in the
and
of the genotype.
One component of the
is genetic
, such as the position
effect.
Another component of the
is
temperature,
and many phenotypes show temperature sensitivity.
In cases of
genomic
, phenotypic expression may depend on the
origin of the chromosome.