Topic 9: Allelic Interactions Flashcards
Complete vs incomplete dominance in terms of heterozygous individuals
complete = phenotype of the het is indistinguishable from the homo dominance phenotype
incomplete = het shows a phenotype intermediate between the corresponding homo phenotypes (blend)
If the F2 generation has PP, Pp, Pp, and pp genotypes and P is dominant, what is the genotype and phenotype ratio for complete and incomplete dominance?
Complete
Geno = 1:2:1
Pheno = 3:1
Incomplete
Geno and pheno = 1:2:1
What is codominance
Heterozygote shows the phenotypic effects of both alleles equally (e.g. roan)
Brown cow crossed with white cow… What would the offspring be in incomplete vs codominance
Incomplete = light brown
Codominance = roan
How are bloodtypes codominant
AB blood type = individual expresses both A and B
Genotypes are IA, IB, and i
IA and IB are codominant (coexpressed)
Slides 7,8
Incomplete vs codominance **
In incomplete dominance, explain the diff alleles
one produces a functional gene product, but not enough (haploinsufficient)
other does not produce a gene product (disfunctional)
How might a trait appear as complete dominance at one level and as codominance at another
E.g. in cystic fibrosis
WT allele produces channel in membrane that regulates Cl levels
Mutant allele produces a mutated channel that stays closed, Cl builds up (cystic fibrosis)
Heterozygotes have enough functional channels to prevent symptoms
What is penetrance
The percentage of individuals having a particular genotype that express the expected phenotype
What is incomplete penetrance
When the genotype does not give the expected phenotype (not 100% of the time)
What is expressivity? e.g.
Degree to which a trait is expressed
e.g. some polydactyly genotypes have full expression, some just have a small nub
What is a recessive lethal allele
Causes death at an early stage of development, so some genotypes may not appear among the progeny
One genotype/phenotype is completely missing
Lethal alleles effect
the mendelian genotypic and phenotypic ratios in progeny
What are multiple alleles/allelic series
Multiple alleles of the same gene generates an allelic series
Will have different dominance relationships within the series
How do we figure out dominance relationships in allelic series
Pairwise monohybrid crosses
