Week 2 Flashcards
Modifications of Mendelian Ratios
define: incomplete dominance
the F1 hybrid resembles neither purebred parent (often an intermediate phenotype)
define: codominance
alternative traits are both visible in the F1 hybrid
what is an example of incomplete dominance
snapdragon colour [red: ArAr, pink: ArAw, white: AwAw]
what is the phenotypic ratio of incomplete dominance and codominance
1:2:1
what is the genotypic ratio of incomplete dominance and codominance
1:2:1
what is the proper way to designate incompletely dominant or codominant alleles
in uppercase
what is the genetic explanation for snapdragon colour displaying incomplete dominance
the allele Ar produces a red pigment and the allele Aw produces a white pigment
what is the mode of colour inheritance if grey parents produce black offspring (cows)
- grey AWAB is heterozygous incomplete dominance phenotype, black is homozygous ABAB
- grey Gg is heterozygous dominant phenotype, black is homozygous recessive gg
is colouring in zebras a result of codominance
no, if it was then there would be pure white and pure black zebras
what alleles are present in ABO blood groups
IA, IB, and i
what dominance relation does ABO blood groups have
IA and IB are codominant to each other and both are dominant to the i allele
why are IA and IB codominant
these alleles code for enzymes that attach A and B sugars to the surface of red blood cells
are variations on complete dominance consistent with Mendel’s law of segregation
yes
define: dominance series
alleles are listed in order from dominant to recessive
how are dominance relationships established
reciprocal crosses between pure-breeding lines
when dealing with multiple alleles with only one wild-type, how is the wild-type allele denoted
with a superscript A+
what is the purpose of doing reciprocal crosses
ensures that the trait is not sex-linked
what are the four rabbit coat colours
agouti, albino, chinchilla, himalayan
how do new alleles arise
through mutation
do different alleles imply different phenotypes
no, a change in the DNA sequence doesn’t always imply a difference in the protein product
define: allele frequency
percentage of the total number of copies of a gene in a population represented by a particular allele
define: wild-type allele
has a frequency of >1%
define: mutant allele
has a frequency of <1%
what is another definition of a monomorphic gene
gene with only one wild-type allele
what is another definition of a polymorphic gene
gene with more than one wild-type allele
define: pleiotropy
multiple phenotypic effects caused by a single gene
what is an example of pleiotropy
sickle cell anemia [destruction of red blood cells, circulatory blockages, and damage to organs]
what does it mean for an allele to be lethal
the allele affects viability in addition to visible phenotype
what is the phenotypic ratio for a heterozygous cross when there is recessive lethal alleles
2:1
what is an example of lethal recessive alleles
Manx cats
in pleiotropy, does being dominant in one phenotype imply it is dominant for all
no, it may be recessive for other phenotypes
what are the phenotypes when there is pleiotropy with 1 dominant and 1 mutant allele
there are multiple phenotypes
define: multifactorial inheritance
a phenotype arising from the action of two or more genes (polygenic) or from interactions between genes and the environment
define: polygenic
a phenotype arising from the action of two or more genes
what is the phenotypic ratio for a trait determined by 2 genes
9:3:3:1
define: complementary gene action
two or more genes can work in tandem, in the same biochemical pathway to produce a particular trait
define: heterogeneous trait
a mutation at any one of a number of genes can give rise to the same phenotype
what are examples of heterogeneous traits
- drosophila body colour (flies)
- pea flower colour
- deafness in humans
- albinism
how can a wild-type phenotype be rescued when it is a heterogeneous trait
complementation
[eeb+b+ (black fly) x e+e+bb (black fly) => e+eb+b (wild-type colour fly)]
what is the phenotypic ratio of complementary genes [ex. pea flower colour]
9:7
define: non-complementation
when two organisms carrying mutations in the same gene for a heterogeneous trait is crossed
define: complementation
two mutants have mutations in differing genes, allowing for wild-type offspring
define: epistasis
a gene interaction in which the effects of an allele at one gene hide the effects of alleles at another gene
define: epistatic
control over another gene
what is an example of recessive epistasis
coat colour in Labrador retrievers [_ _ ee => yellow, B_E_ => black, bbE_ => brown]
what is the phenotypic ratio of recessive epistasis
9:3:4
what does recessive epistasis look like in human blood groups
H/h controls production of lipid H to which A and B sugars are attached, hh means the lipid is not produced
example of blood types:
IA_hh => type O
IA_Hh => type A
what is an example of dominant epistasis
summer squash colour [C_ => white, ccG_ => yellow, ccgg => green]
what are the hypothesis testing rules
- true breeding homozygous parents will produce heterozygous F1 offspring
- test cross F1 heterozygotes
- phenotypic ratios of F2 indicate the mode of inheritance
how do you find the genotype of an F2 individual showing recessive epistasis
cross it with an individual that is known to be homozygous for the recessive allele of the masked trait and homozygous for the antagonist trait (_ _ cc x bbCC)
what is a way to find inheritance mode in humans since test-crossing is not possible
pedigree analysis
does the same genotype always result in the same phenotype
no, there are other influences such as the environment, modifier genes, and chance
define: penetrance
percentage of the population with a particular genotype that demonstrate the expected trait
define: expressivity
the degree or intensity with which a particular genotype is expressed in a phenotype within a population
what is an example of variable expression
- coat pattern in beagles
- retinoblastoma (75% penetrance, 30% expressivity or getting it in one eye)
define: sex-linked traits
due to genes on the X or Y chromosome
what are examples of sex-linked traits
- hemophilia
- colour blindness
define: sex-limited trait
affect a structure of process that is found in one sex but not the other
what are examples of sex-limited traits
- bright plumage in male birds
- traits involving milk production
- traits involving horns/antlers
define: sex-influenced traits
show up in both sexes but their expression may differ between the two sexes
what are examples of sex-influenced traits
- pattern baldness
- height
how does pattern baldness differ between men and women
baldness is dominant in men and recessive in women
how does the genotype affect pattern baldness in men
if it is heterozygous, the onset is later than homozygous dominant
what is an example of the environment affecting the phenotypic expression of a genotype
Himalayan coat pattern in cats and rabbits, cooler temperatures are required to produce melanin => dark fur
define: conditional lethality
an allele which is lethal under only certain conditions
define: restrictive [conditional lethality]
conditions that contribute to lethality
define: permissive [conditional lethality]
conditions that don’t contribute to lethality
what is an example of a conditionally lethal allele
malignant hyperthermia, genetic disease triggered by certain anaesthetics
