Chapter Two: Extensions to Mendel Flashcards
dominance is not always ___
complete
crosses between true-breeding strains can produce hybrids with phenotypes ___ from both parents
different
F1 hybrids that differ from both parents express an intermediate phenotype
incomplete dominance
F1 hybrids express phenotype of both parents equally
codominance
in incomplete dominance and codominance, phenotypic ratios and genotypic ratios are ___
the same
snapdragon flower color is an example of ___
incomplete dominance
lentil coat pattern is an example of ___
codominance
ABO Blood group is an example of ___
codominance
dominance relations affect ___ and have no bearing on the ___ of alleles
phenotype
segregation
alleles still segregate ___ even without incomplete dominance
randomly
can a gene have more than two alleles
yes
genes may have ___ alleles that segregate
multiple
although there can be many alleles in a population, each individual carries ___
only two of the alleles
there are ___ alleles for blood type and ___ possible genotypes that generate ___ possible phenotypes
three
six
four
dominance relations are ___ to a certain pair of alleles
unique
in order to establish dominance relations, you perform ___ between ___ of al phenotypes
reciprocal crosses
pure-breeding lines
where do new alleles come from
mutations
multiple alleles arise spontaneously from ___
mutations
chance alterations in genetic material
mutations
the percentage of the total number of gene copies represented by one allele
allele frequency
allele whose frequency is more than 1%
wild-type
allele whose frequency is less than 1%
mutant allele
gene with only one wild-type allele
monomorphic
gene with more than one wild-type allele
polymorphic
one gene may contribute to ___
several visible characteristics
when a single gene determines more than one distinct and seemingly unrelated characteristic
pleiotropy
a syndrome is defined as something that has many symptoms because ___
multiple organ systems are impacted by the disease
type of pleiotropy where alleles produce a visible phenotype and affect viability
lethality
alleles that produce viability often produce deviations from typical ___ predicted by mendel’s laws
ratios
inheritance of coat color in mice is an example of ___
pleiotropy
recessive lethal alleles are not as ___ as other alleles because ___, changes the ___
viable
progeny normally don’t survive until birth
ratio
more than ___ mutant alleles have been identified so far for sickle cell
400
normally wild type allele for sickle-cell ___
HbBA
HbBS allele specifies for an abnormal protein that causes ___
sickling along red blood cells
the most common mutant allele for sickle-cell substitutes an amino acid with a ___ for one with a ___, which changes its ___
negative charge
neutral charge
shape
HbBS affects more than one ___
trait
the advantage of heterozygotes for sickle-cell
resistant to malaria
it is difficult to get rid of a ___ when carriers have an advantage
deleterious allele
___ can emerge from the combination of alleles of two genes
novel phenotypes
two genes work together to produce a phenotype
complementary gene action
___ ratio is a phenotypic signature of complementary gene interaction where dominant alleles of two genes act together to produce a trait while the other three genotypic classes do not
9:7
a 9:7 ratio demonstrates that ___ must be present to produce a trait
one dominant allele of each gene
when one gene’s allele mask the effects of another gene’s alleles
epistasis
Labrador retriever coat color is an example of ___
recessive epistasis
labrador retrievers:
B allele is ___ and determines ___
b allele is ___ and determines ___
E allele is ___ and determines ___
e allele is ___ and determines ___
dominant, black
recessive, brown if homozygous
on a second gene, no effect
recessive, hides brown or black is homozygous
9:3:4 is a telltale ratio of ___
recessive epistasis
the expected phenotypic ratio for recessive epistasis of lab coat color is ___
9 black (B_E_): 3 brown (bbE_): 4 gold (__ee)
epistasis in human blood groups: two parents who are apparently O can have offspring that are ___ because of the ___
type A or B on occasion
bombay phenotype
the Bombay phenotype is a ____ at a ___ that masks the phenotype of ___ if it is homozygous recessive
mutant recessive allele
second gene
ABO alleles
presence of dominance allele at second gene hides the affects of alleles at an original gene
dominance epistasis
12:3:1 and 13:3 are telltale ratios for ___
dominance epistasis
it is not always possible to determine ____ mutated in a person with a heterogenous mutant phenotype
which of many genes
deafness in humans may be caused by a mutant allele at one of more than ___ different genes
50
___ can determine if mutations arise from the same or different genes
complementation testing
human deafness: if parents have a defect in the same gene, their offspring will ___. if parents have a defect in different genes, their offspring will ___.
all be deaf
possibly be hearing
four distinct F2 phenotypes
additive
when homozygous, recessive allele of one gene masks both alleles of another gene
recessive epistasis
when homozygous, recessive allele of each gene masks the dominant allele of the other gene
reciprocal recessive epistasis
dominant allele of one gene hides effects of both alleles of the other gene
dominant epistasis I
dominant allele of one gene hides effects of dominant allele of another gene
dominant epistasis II
only one dominant allele of either of two genes is necessary to produce phenotype
redundancy
how do we know if a trait is caused by one gene or two genes that interact
ratios like 9:7 or 13:3 indicate gene interaction
look at different ratios to determine which is correct
additive gene interaction ratio
9:3:3:1
recessive epistasis ratio
9:3:4
reciprocal recessive epistasis ratio
9:7
dominant epistasis I ratio
12:3:1
dominant epistasis II ratio
13:3
redundancy ratio
15:1
disease that produces little or not pigmentation in skin, hair, and eyes
ocularcutaneous albanism (OCA)
the same genotype doesn’t always produce ___
the same phenotype
phenotype often depends on ___ and ___
penetrance and expressivity
percentage of a population with a particular genotype that show the expected phenotype
penetrance
penetrance can be ___ or ___
complete or incomplete
degree or intensity with which a particular genotype is expressed in a phenotype
expressivity
have subtle, secondary effect on a phenotype from a major gene
modifier genes
environment can affect the ___ of a genotype
phenotypic expression
___ is a common element of the enrichment that affects phenotype
temperature
example of temperature impacting phenotype
coat color in siamese cats is darker in its extremities (legs, tail, ears)
why do the colors differ in siamese cats
mutation that renders an enzyme involved in melanin synthesis is temperature sensitive
change in phenotype arising from environmental agents that mimics the effect of a mutation at a gene
phenocopy
mutations that are lethal only under some conditions
conditional lethal
mutant allele has wild-type functions (normal)
permissive conditions
mutant allele has defective functions
restrictive conditions
traits determined by segregating alleles of many genes interacting with one another and the environment
continuous traits
example of continuous traits in humans
height and skin color
continuous traits are also called ___ and are usually ___
quantitative traits
polygenic
the more genes that contribute to a trait, the greater number of ___ and the greater similarity to ___
possible phenotypes
continuous variation
continuous variation phenotypic rations will exhibit a ___
bell curve
domestic dog coat colors provide a clear example of a ___
complex trait
there are at least ___ genes that control for coat color and pattern in dogs
12
skin cells that produce pigments deposited in each dog hair
melanocytes
melanocytes can produce either ___ or ___
dark pigment (eumelanin) or light pigment (pheomelanin)
genes E, A, and K control ___
the switch between light and dark pigment synthesis in melanocytes
genes E and B control ___
synthesis and deposition of the dark pigment eumelanin
genes S and M control ___
spotting
the F1 phenotype generated by a pair of alleles defines the ___ between alleles
dominance relationship
incomplete dominance: F1 resembles ___
codominance: F1 resembles ___
neither parent
components of each parent
one gene can contribute to ___
multiple traits
a single gene may have many ___
alleles
new alleles arise by ___
mutation
wild type alleles ___ 1% of the population. mutant alleles ___ 1% of the population
more then
less then
two or more wild type alleles in the population
polymorphic gene
a gene with only one wild type allele
monomorphic
two or more genes may interact to produce a ___
phenotype
when the action of an allele at one gene hides traits normally caused by alleles at another gene
epistasis
when dominant alleles of two or more genes are required to generate a trait
complementary gene action
with ___, mutant alleles at any one of two or more genes are sufficient to elicit a phenotype
heterogeneity
___ can reveal whether a particular phenotype arises from mutations in the same or separate genes
complementation tests
expression of phenotypes can be modified by ___, ___, or ___
environment, chance, or other genes
when fewer than 100% of individuals with the same genotype express a specific phenotype
incomplete penetrance
a phenotype may show ___ when it is expressed at a different level in different individuals with the same genotype
variable expressivity
a ___ trait can have any value of expression between two extremes, most are ___
quantitative
polygenic
