Genetics Flashcards
Outline the multiple gene hypothesis.
A hypothesis to explain quantitative variation by assuming the interaction of a large number of genes (polygenes) each with a small additive effect on the character.
Define polygenes and multiple genes. What’s the difference?
Multiple alleles are more than two alternative forms of a gene, located at the same loci of homologous chromosomes. In polygenic traits, several genes are involved in determining a single trait . Multiple alleles follow complete dominance or codominance while polygenic traits follow codominance or incomplete dominance.
Define heritability h2.
The heritability of a trait is the proportion of the total variance in phenotype due to genetics factors.
What is GWAS?
What type of genetic variation is used in GWAS?
SNPs
Outline penetrance and expressivity, reference examples.
- Penetrance; is the percentage of individuals having a specific genotype who express the associated phenotype.
- Complete penetrance; occurs when the genotype is expressed by every individual with that genotype(e.g. Marian syndrome; complete and variable in expression).
- Incomplete penetrance; is when some individuals with a genotype show no effect of that genotype on the phenotype(e.g. polydactyly; incomplete and variable in expression).
- Expressivity; is the degree to which the trait is expressed.
- Variable expressivity; means that individuals who express a genotype exhibit variation in their phenotypes
Distinguish between narrow and broad-sense heritability.
The broad-sense heritability is the ratio of total genetic variance to total phenotypic variance.The narrow-sense heritability is the ratio of additive genetic variance to the total phenotypic variance.
What is the additive effect?
A mechanism of quantitative inheritance such that the combined effects of genetic alleles at two or more gene loci are equal to the sum of their individual effects.
Define fibroblast and sonic the hedgehog. Distinguish between the two.
