EXTENSION OF MENDELIAN INHERITANCE(lesson 1) genetics Flashcards
Prevalent alleles in a
natural population.
Wild-type alleles
more than one
wild-type allele may occur
Genetic polymorphism-
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
- much less common than recessive
mutant alleles.
Dominant mutant allele
is usually caused by a mutant
allele.
genetic disease
Three explanations account for most dominant mutant
alleles:
Gain-of-function mutation
* Dominant-negative mutation
* Haploinsufficiency.
*Change the gene or the protein encoded by a gene
so it gains a new or abnormal function.
Gain-of-function mutation
*Change a protein such that the mutant protein acts
antagonistically to the normal protein.
Dominant-negative mutations
The dominant mutant allele is a loss-of-function
allele.
Haploinsufficiency
used to describe patterns of
inheritance in which a heterozygote
- An example in humans is polydactyly.
Haploinsufficiency
which an allele that is expected to cause
a particular phenotype does not.
INCOMPLETE PENETRANCE
Human pedigree for a dominant trait
known as
polydactyly
due to an autosomal
dominant allele—
Polydactyly
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-
often due to environmental
influences and/or due to effects of modifier genes
INCOMPLETE PENETRANCE
The
phenotypic effects are dependent on
the temperature
Temperature-sensitive allele.
caused by a defect in
a gene that encodes the enzyme
phenylalanine hydroxylase.
Phenylketonuria (PKU)
which is found in most protein-rich
foods,
phenylalanine,
A condition in which the phenotype is
intermediate between the corresponding
homozygous individuals.
INCOMPLETE DOMINANCE
German botanist ____ first
observed this phenomenon in the color of the
flowers of the four-o’clock plant (Mirabilis
jalapa)
Carl Correns
lack of
a functional protein required for pigmentation.
Heterozygote Advantage/ OVERDOMINANCE
which the affected individual produces
an altered form of the protein hemoglobin, which
carries oxygen within red blood cells.
Sickle cell disease-
This causes their red
blood cells to deform into a
sickle shape under
conditions of low oxygen concentration
Individuals affected with sickle cell
disease are
homozygous for the HbS allele
high frequency among human populations
that are exposed to malaria.
OVERDOMINANCE
spends part of its life
cycle within the Anopheles mosquito and another part within the red blood
cells of humans who have been bitten by an infected mosquito.
malaria, Plasmodium,
, are likely to rupture
when infected by this parasite, thereby preventing the parasite from
propagating.
HbA HbS
two
alleles are both expressed
in the heterozygous
individual
CODOMINANCE
when a gene is located on the X
chromosome but not on the Y chromosome.
X-linked inheritance
to indicate that males have a single copy of an X-linked gene
Hemizygous
is that males are more likely to be
affected by rare, recessive X-linked disorders.
X-linked inheritance
X-linked recessive, the allele causing
the disease is recessive and located on the X chromosome
Duchenne muscular dystrophy-
refers to a gene that is found on one of the two types
of sex chromosomes but not on both.
Sex-linked gene-
relatively few genes are located only on the
Y chromosome.
Holandric genes
found in mammals.
SRY gene
Its expression is necessary for proper
male development.
SRY gene
which an allele is dominant
in one sex but recessive in the opposite sex.
Sex-influenced inheritance-
controlled by sex hormones or by the pathway
that leads to male and female development
Sex-limited inheritance-
The genes that affect sex-limited traits maybe
autosomal or X-linked
are the presence of ovaries in
females and the presence of testes in males.
sex-limited traits
which members of the
opposite sex have different morphological features.
Sexual dimorphism
has the potential to cause the death of an
organism.
LETHAL ALLELES
one that must be present for survival
Essential gene-
not absolutely required for survival, although they
are likely to be beneficial to the organism.
Nonessential genes-
some lethal alleles may kill an organism only
when certain environmental conditions prevail
Conditional lethal alleles-
conditional lethal alleles
cause an organism to die only in a particular temperature range.
Temperature-sensitive (ts) lethal alleles-
may also be identified when an individual is
exposed to a particular agent in the environment.
lethal alleles-
People with a defect in the gene that encodes the ____ have a negative reaction to the
ingestion of ____.
enzyme glucose-6-phosphate dehydrogenase (G-6-PD)
fava beans
lethal alleles act only in some individuals.
Semilethal alleles-
multiple effects of a single gene
PLEIOTROPY
all traits are affected by
the contributions of many genes.
GENE INTERACTIONS
