5/6/25 Flashcards
(47 cards)
what is the heterozygote advantage
it is where the heterozygote genotype has an advantage over the homozygous cross
when is heterozygote advantage most apparent
it is most apparent under selective pressure for disease
what are the three explanations for overdominance/heterozygote advantage
disease resistance, homodimer formation, variation in functional activity
for heterozygote advantage, how does disease resistance work
the heterozygotes have slightly reduced protein functions that help prevent infections
what are two examples of heterozygote gene advantage in relation to disease resistance
sickle cell anemia and malaria
tay-sachs disease and tuberculosus
why does a carrier for tay-sachs disease have resistance to tuberculous
the heterozygotes are resistant to the infection
what is the advantage for heterozygote homodimer formation (A1A2 example)
heterozygote A1A2 can form A1A1, A2A2, and A1A2 homodimers that have better functional activity
what is an example for variation in functional activity in heterozygote advantage (E1 E2 allele and temperature)
the E1 allele functions at low temperatures while E2 functions at high temperatures. The heterozygote E1E2 has the advantage that it can function over a broad range of temperatures
what is incomplete penetrance
a dominant allele is not expressed in a heterozygote individual
what is an example of incomplete penetrance
polydactyly, some individuals show the phenotype while others don’t
why does incomplete penetrance exist?
similar to semi-lethal alleles, the background genetics play a role in suppressing traits
if 60% of heterozygotes with a dominant trait show the phenotype, what does this tell us about the penetrance and incomplete penetrance
it tells us there is 60% penetrance and 40% incomplete penetrance
what is expressivity?
it is the degree to which a trait is expressed
if someone with polydactylyl has low levels of extra digits, how much expressivity do they have?
they have low expressivity
what causes expressivity and incomplete penetrance?
the environment and genes
provide an example of the environmental influence on genes
the disease phenylketonuria can be repressed in phenotype when the newborn is put on a specific diet early on
what are pleiotropic effects
it is where a single gene generates multiple effects on the phenotype
one gene = multiple phenotypes
what are gene interactions
they are when two or more genes influence the outcome of a single trait
what is epistasis
it is when one gene will mask the phenotypic effect of another
where do epistatic interactions usually arise from
they arise when two or more different proteins participate in a common cellular function
in an epistatic interaction between two genes in a common pathway, if one gene is a homozygote recessive, what is the result
the other gene in the pathway will be blocked and not produce the phenotype
what is complementation
it is where each parent provides a functional copy that complements the mutated copy of the other, this allows the wildtype dominant phenotype to be expressed
how is complementation normally observed
when both parents have a recessive phenotype and their offspring have a wildtype phenotype
what does complementation show?
it tells us that two mutated lines had the same phenotype cause by mutations in DIFFERENT genes, one parent compensates for the mutation in the other
