Dominance
- when the two different alleles are present in a genotype. only the trait encoded by the dominant allele is observed in the phenotype
- the result of the interactions between alleles at the same locus
- only influences the way genes are expressed in the phenotype
Incomplete/Partial Dominance
- the phenotype of the F1 is intermediate to that of the two parents. NOT A BLEND
- egg plant
- purple, violet, white (no pigment)
Codominance
- the heterozygote simultaneous expresses the phenotypes of both homozygotes.
- Basically both the two alleles are dominant
MN blood type
- L^M encodes M antigen
- L^N encodes N antigen
- L^M L^M expresses M
- L^N L^N expresses N
- L^M L^N expresses both M and N
penetrance
the proportional of individuals with a specific genotype who manifest that genotype at the phenotypic level.
incomplete penetrance
have the genotype for something but not expressed phenotypically
expressivity
- the degree to which a particular genotype is expressed
- small tag of skin compared to full fingers and toes
fatal trait
will eventually kill the individual (after birth)
lethal trait
will kill the individual before birth
allelic series
- multiple alleles in a population for some loci
- a greater variety of genotypes and phenotypes is possible
- inheritance is the same as that encoded by the two alleles
The ABO group
I^A - encodes A antigen
I^B - encodes B antigen
i - encodes no antigen
I^A and I^B are codominant to each other and both are dominant to i
Universal donor
O
Universal Acceptor
AB
Gene frequently exhibit
independent assortment but do not act independently in their phenotypic expression
gene interaction
- the effects of genes at one locus depend on the presence of genes at other loci
- the products of genes at different loci combine to produce new phenotypes that are not predictable from single-locus effects alone
epistasis
when the effects of one gene at one locus hides/masks the effect of another gene at a different locus
epistatic gene
the gene that does the masking
hypostatic gene
the gene whose effect is masked
single recessive epistasis
- the homozygous recessive condition at one locus masks or modifies the expression of alleles at the second locus
- if you have aa in mice, the mouse will be white regardless of what is at B
The Bombay phenotype
- two recessive alleles inhibit the expression of alleles at a different locus
- homozygous for h encodes a defective enzyme. The defective enzyme is incapable of making h and because H is not produced, no ABO antigen is synthesized
The expression of ABO alleles depend on
- the genotype at the H locus.
Individuals with hh at the H locus will have what type of blood
They will have O type blood no matter what alleles they carry at the ABO locus
single dominant epistasis
- only a single copy of an allele is required to inhibit the expression of the allele at a different locus
- W_Y_ and W_yy do not produce enzymes.
- wwyy produces enzyme 1 but not enzyme II
- wwY_ produces enzyme I and enzyme II.
- if the dominant allele is present, the enzyme is not expressed at the very start.
How to work an epistasis problem
- start by giving data from F2 of a dihybrid cross. F1 AaBb then cross them to get F2
- Determine the total # of progeny
- Divide the # of each phenotype by the total number of progeny
- Multiply by 16
- Form hypothesis as to type of epistatis
