Deviations from Mendelian Genetics Flashcards
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
