genetics midterm lesson 1 Flashcards
Prevalent alleles in a
natural population.
* Example: Elderflower orchid,
Dactylorhiza sambucina
Wild-type alleles
more than one
wild-type allele may occur
Genetic polymorphism
tend to promote the
reproductive success of organisms in
their native environments.
Wild-type alleles
random mutations occur
in populations and alter preexisting
alleles. Called as such to distinguish
them from the more common wild-type
alleles
Mutant alleles
usually cause a substantial decrease in the expression of a functional protein supported by the analysis of many
human genetic diseases.
Recessive mutant alleles
is usually caused by a mutant
allele.
genetic disease
much less common than recessive mutant alleles.
Dominant mutant allele
- Gain-of-function mutation
- Dominant-negative mutation
- Haploinsufficiency.
Three explanations account for most dominant mutant
alleles :
*Change the gene or the protein encoded by a gene
so it gains a new or abnormal function. For
example, a mutant gene may be overexpressed or it
may be expressed in the wrong cell type.
Gain-of-function mutations
*Change a protein such that the mutant protein acts
antagonistically to the normal protein. In a
heterozygote, the mutant protein counteracts the
effects of the normal protein, thereby altering the
phenotype.
Dominant-negative mutations
- The dominant mutant allele is a loss-of-function
allele.
Haploinsufficiency
used to describe patterns of
inheritance in which a heterozygote (with one
functional allele and one inactive allele) exhibits an
abnormal or disease phenotype.
Haploinsufficiency
An example in humans is polydactyly.
Haploinsufficiency
allele that is expected to cause
a particular phenotype does not.
INCOMPLETE PENETRANCE
The measure of penetrance is described at the
population level. For example, if 60% of the
heterozygotes carrying a dominant allele exhibit the
trait, we say that this trait is 60% penetrant.
INCOMPLETE PENETRANCE
At the individual level, the trait is either present or not.
INCOMPLETE PENETRANCE
Human pedigree for a dominant trait
known as
polydactyly
This trait causes the affected individual to
have additional fingers or toes (or both)
polydactyly
the allele is found in a
gene located on an autosome (not a sex
chromosome)
autosomal dominant allele
a single copy of this
allele is sufficient to cause this
condition.
autosomal dominant allele
term used to describe the outcome of traits is the degree to which the trait is expressed
Expressivity
goes through two color
phases. During the cold winter, it is
primarily white, but in the warmer
summer, the fox is mostly brown
arctic fox (Alopex lagopus)
The
phenotypic effects are dependent on
the temperature
Temperature-sensitive allele
is caused by a defect in
a gene that encodes the enzyme
phenylalanine hydroxylase.
Phenylketonuria (PKU)- autosomal
recessive disease
