Deviations from Mendelian Genetics Flashcards
(28 cards)
Calculating the number of possible genotypes in a population
Possible genotypes= [n(n+1)]/2
n= # of alleles
Incomplete dominance
Phenotype of heterozygote is intermediate to homozygotes
Ex- palomino horses (intermediate to chestnut and cremello)
Gene dosage and incomplete dominance
Homozygosity for functional allele causes 2 doses of gene product
Heterozygosity causes 1 dose (intermediate)
Homozygosity for nonfunctional allele causes no doses
Haplosufficiency
1 dose of gene product supports life Autosomal recessive Homozygous wt= healthy Heterozygous= healthy Homozygous mutant= sick or dead
Haploinsufficiency
1 dose of gene product isn’t enough to support life
Homozygous wt= healthy
Heterozygous= sick or dead
Homozygous mutant= sick or dead
Essential gene
Gene that encodes a product that is required for life
When mutated, causes lethal phenotype
No complementary gene (no backup genes)
Lethal allele
Presence of this results in death
Recessive lethal
Need 2 copies of lethal allele to exhibit lethal phenotype
Most truly recessive lethals are lethal in utero (kill baby before it’s born)
Dominant lethal
Both homozygotes for allele and heterozygotes display lethal phenotype
Caused by a gain of function mutation or dominant negative mutation
Codominance
Heterozygote shows the phenotypes of both homozygotes simultaneously
Ex- roan horses (both red and white hairs)
Molecular explanation of codominance
Equally strong expressed gene products that don’t block or interfere with the cellular functions of each other
Pleiotropy
1 gene is responsible for multiple phenotypes
Selective sweeps
When 2 or more genes show strong linkage and 1 of the 2 genes has an allele that gives a selective advantage, the other allele tends to be inherited with the advantageous allele
“Genetic hitchhiking”
Polygenic trait
Trait that results from action by multiple genes
Most traits are these
Epistasis
1 gene masks the expression of another gene
Polygenic phenomenon
Recessive epistasis
Homozygous recessive genotype at locus A masks phenotypic expression at locus B
aaB- and aabb have same phenotype
9:3:4 phenotypic ratio
Dominant epistasis
Presence of the dominant allele at locus A masks phenotypic expression at locus B
A-B- and A-bb have same phenotype
Synthetic lethal and negative epistasis
2 mutations together cause the death of the organism
Mutation A or mutation B- alive
Mutation in both A and B- dead
B masks a and A masks b
Molecular explanation of synthetic lethal/negative epistasis
Wild-type gene products are involved in complementary pathways (1 can no longer compensate for the other)
Modifier gene
Alters the expression of a second gene
Can suppress or enhance phenotypic expression
Norm of reaction
Range of potential phenotypes for a particular genotype
Penetrance
The % of individuals with a particular genotype who show the expected phenotype
Expressivity
Degree to which a phenotype is expressed
Severity of phenotype
Position effect
Physical location of a gene can influence expression
Next to highly expressed areas- gene will be highly expressed
