Basic Principles and extensions Flashcards
Null allele
Nonfunctional
Hypomorphic allele
partial function
Enzyme or other protein is no longer being produced, produced at a lower rate
or is nonfunctional
Gain of function mutation
Increased detrimental function
Haplosufficiency
Half as much protein is synthesized yet is often enough to achieve the wildtype phenotype
Haploinsufficiency
Protein synthesized is not enough for normal phenotype
Recessive lethal alleles
Essential genes that when mutated can lead to a lethal phenotype
2 copies needed for it to be lethal
Huntingtons
Dominant lethal alleles, degenerative with late onset of symptoms
Recessive amorphic
Loss of function allele that does not produce a functional polypeptide
Severe mutant phenotype
Recessive hypomorphic
Loss of function allele produces a partially functional polypeptide
mild mutant phenotype
Dominant negative
Allele produces polypeptide that interferes with wild type
Severe mutant phenotype
Penetrance
Proportion of individual organisms having a particular genotype that expresses the phenotype, variation in the population
Polydactyly is an example of variable penetrance8
Expressivity
Degree to which a phenotype is expressed, variation in the indivual
Split hand/foot syndrome are rare autosomal dominant disorders that shows variable expressivity
Norm of reaction
Range of phenotypes expressed by a single genotype under different environmental conditions
Temperature sensitive allele
Siamese allele in cats
Phenocopy
Change in phenotype arising from environmental factors that mimic the effects of genetic mutation
Complementation
Occurs when 2 strains of an organisms with different homozygous recessive mutations that produce same phenotype produce offspring of the wildtype phenotype when crossed
Only occur when mutations are in different genes
Genetic epistasis
Masking of the expression of one gene by another. No new phenotypes are produced
F2 phenotypic ration 9:3:4
Recessive epistasis
F2 phenotypic ration 12:3:1
dominant epistasis
f2 phenotypic ration 9:7
Complementation
Pleiotropy
Single gene responsible for multiple distinct and seemingly unrelated phenotypic effects
sickle cell disease and cystic fibrosis
Inbreeding
Reveals recessive alleles that have been masked before
Inbreeding depression
Occurs in plants
may not be able to adapt to environmental change and more susceptible to wide spread disease (monoculture)
Hetersosis
When 2 different inbred lines are crossed they form heterozygotes for several genes and express hybrid vigour
Hardy-Weinberg principle
Prediction of genotypes through measure of allele frequencies
p^2+2pq+q^2 =1
f(A)=p f(a)=q f(AA)=p^2 f(Aa)=2pq f(aa)=q^2
Holds true but only in the absence of evolutionary infulences
Dosage compensation
Way of equalizing gene expression in the face of different gene dosage
X and Y chromosomes pair during meiosis even though they are not homologous
Chromosomal sex-determination
In insects, sex determined by raito of x chromosomes Males have a single x females have 2
In mammals, sex has to do with presence of Y chromosome
X-inactivation
If a cell contains 2 or more x chromosomes, all but one of them are inactive
