Lecture 3-5 Flashcards
What is complete dominance
one who carries the dominant allele, no matter homo or hetero, will display the dominant trait
(ie. BB=Bb but bb is different)
What is incomplete dominance
BB, Bb, and bb all differ phenotypically, where the heterozygote is an intermediate between homo dominant and homo recessive
(ie. BB=red, Bb=pink, bb=white)
What is codominance
BB, Bb, and bb all differ phenotypically, but Bb exhibits phenotypes of both homozygotes
(ie. blood type)
What is a dominance/allelic series
< and > indicate dominance while = indicates codominance in a series of allele pairs for a given organism or species
What is a wild type allele
the “normal”
What is a loss of function allele
protein is no longer produced, protein is reduced in fewer proportion, or protein is non functional
What is haplosufficiency
if you have one wild type allele and one loss of function allele, there is still a sufficient amount of wild type of produce a normal phenotype
What is haploinsufficiency
when the dominant gene causes a loss of function, so half as much protein is synthesized but it is not enough to produce wild type phenotype
What is a recessive lethal allele
only lethal in homozygotes
(ie. the ts allele in Tay Sachs is the mutated allele, so tsts is lethal, but TSts isn’t and neither is TSTS)
What is a dominant lethal allele
expressed in either the homo or hetero, depending on which allele is dominant
(ie. the B allele in Huntingtons is the mutated allele, so BB is lethal and Bb is lethal)
What is penetrance
the proportion of individual organisms having a particular genotype that express the expected phenotype
*in sum; variation in the population
What is expressivity
the degree to which a phenotype is expressed in an individual
*in sum; variation in the individual
What is complete penetrance
one phenotype is completely penetrant in a population
What is incomplete penetrance
identical known genotypes in a population yield less than 100% expected phenotype
ie. in a population of brown fur, a few in the population are white, regardless of same genotype
What is constant expressivity
all identical genotypes with no expressivity effect have 100% the same phenotype
What is variable expressivity
when identical known genotypes have a variability effect that yield a range of phenotypes
ie. a brown population with a variability effect has different shades of brown regardless of same genotype
If long fingers are inherited as a recessive trait with 80% penetrance, what are the chances that two heterozygotes would produce an offspring with long fingers
1/4 chance of being homozygous recessive
1/4 x 80% = 20%
What are some environmental affects on expressivity and penetrance
age
sex
temperature
chemicals
What is the norm of reaction
the range of phenotypes shown by a single genotype under different environmental conditions
What is a phenocopy
a change in phenotype arising from environmental factors that mimic the effects of a mutation
What is Mendels law of independent assortment
the inheritance of one trait will not impact the inheritance of another trait
ie. AaBb x AaBb type crosses
What is the ratio of offspring in the F2 generation of independent assortment between RRYY and rryy
9:3:3:1
What is the Mendalian ratio
9:3:3:1
If you have complete dominance in two gene pairs contributing to one singular trait, how many phenotypes are seen
4…
full dominant
heterozygous (dominant in one)
heterozygous (dominant in the other)
full recessive
What is complementation
two strains of an organism with DIFFERENT homozygous recessive mutations that produce the same phenotype, mate and produce offspring of the wild type phenotype
What is the catch to complementation
the mutations in the two parentals must be in DIFFERENT genes
What is the logic behind complementation - how is a wild type produced from two mutated organisms
the other genome supplies the wild-type allele to “complement” the mutated allele
When will complementation NOT occur
if the parental mutations are in the same gene
Give an example of complementation using genes A and B (theoretic example)
if one parent is AAbb, and the other parent is aaBB, each parent has the recessive mutation, just on a different gene (one in aa and one in bb)
when these parents mate, offspring of AaBb can be produced, to form the wild type phenotype
If you see a 9:7 ratio on a test question, what should be investigated
complementation
What is a heterogenous trait
a mutation in any one of a number of genes can give rise to the same phenotype
For complementation to work, what must occur in the parental genes
each must have a mutation on DIFFERENT genes
each must be dominant in the other gene
What is the compliment ratio
9:7
What is epistasis
the masking of the expression of one gene by another
What does the epistatic gene do and what does the hypostatic gene do
epistatic = does the masking
hypostatic = is masked
What is the recessive epistatic ratio
9:3:4
What is the dominant epistatic ratio
12:3:1
Explain recessive epistasis
the recessive gene of one trait masks the gene of the other trait
ie. if referring to A/a C/c genes, recessive c would mask any phenotype of A/a
- so, any time a recessive c occurs, the phenotype of A/a is masked… c is the epistatic gene and a is the hypostatic gene
Explain dominant epistasis
the dominant gene of one trait masks the gene of the other trait
ie. if referring to W/w B/b genes, dominant W would mask the phenotype of B/b regardless of the dominance
- so, any time a dominant W occurs, the phenotype of B/b is masked…W is the epistatic gene and B is the hypostatic gene
What are the monohybrid ratios for complete dominance, incomplete dominance, and codominance, as well as recessive lethal alleles
complete: 3:1
incomplete: 1:2:1
codominance 1:2:1
recessive lethal: 2:1
What are the dihybrid ratios for complete dominance, recessive epistasis, dominant epistasis, and complementation
complete: 9:3:3:1 (Mendelian ratio)
recessive epistasis: 9:3:4
dominant epistasis: 12:3:1
complementation: 9:7
What is pleiotropy
a single mutated gene is responsible for a number of distinct and seemingly unrelated phenotypic effects
ie. sickle cell disease and cystic fibrosis
What is consanguineous mating
inbreeding
What is heterosis
two different inbred lines are crossed, creating heterozygous products
What happens frequently with inbreeding
higher frequency of homozygotes, fewer frequency of heterozygotes
