Quantitative Genetics Flashcards
(14 cards)
What is quantitative genetics?
The study of the inheritance of characters that do not fall into distinct classes
How does expression of quantitative genotypes work?
two alleles for each locus - a + that increases a trait and a - with no effect. E.g.
4 plus 0 minus = red
3 plus 1 minus = Light red
2 plus 2 minus = pink
1 plus 3 minus = Light pink
0 plus 4 minus = white
What is the genetic basis of a normal distribution of individuals on a scale for a certain trait?
No. genotypes is still 3^n loci but no phenotypes changes: e.g. 5 loci, 3^5 genotypes, but 11 phenotypes as Possible to achieve 10 pluses or 0 pluses in only one way each (++.++.++.++.++ and –.–.–.–.–.) For five plus and five minus there are 51
possible genotypes. (E.g. +-.+-.+-.+-.+- or ++.++.+-.–.–.) so intermediate phenotypes at the middle of the curve more common.
What is the relationship between % of population a standard deviations from the mean?
68.3% of the population should lie ± 1 standard
deviation from the mean and 95.5% of the population lie ± 2 standard deviations of the mean.
How is variance calculated?
Sum of the squares of the deviation from the mean for each value, over the total number of values.
What is heritability and what equation is used to find it?
The proportion of the total phenotypic variance which is due to genetic
variance. H2 = VG / VP
Give an example of the interaction of genes and environment in heritability
Achillea (yarrow): Several sets of genetically identical cuttings from various altitudes planted at varying altitudes show variation in height, showing different responses to different altitudes depending on genotype.
How is the total phenotypic variance calculated?
The total phenotypic variance (VP) is a result of variance caused by the environment (VE), the genes (VG)
and the interaction of the gene and environment (VGE), in other words:
VP = VE + VG + VGE.
thus,
H^2 = VG / VG + VE + VGE
What does the total genetic variance consist of?
additive genetic variance, dominance genetic variance and interaction genetic variance
What is additive genetic variance?
(Va): variance associated when the addition of an allele contributes a fixed value to the value quantitative trait: ++ = 2cm; +- = 1cm; – = 0cm
What is dominance genetic variance?
(Vd): variance caused by the masking of recessive alleles by dominant alleles in the heterozygote: ++ = 2cm; +- = 2cm; – = 0cm
What is interaction genetic variance?
(Vi): variance caused by the interaction between different loci. Combinations of alleles at different loci produce effects that aren’t predictable from each gene alone.
It complicates predicting traits, since the influence of one gene might change depending on the genetic background.
What is the difference between broad and narrow sense heritability?
H^2 = VG / VG + VE + VGE. h^22 = Va / VP
Farmers are more interested in narrow sense heritability is it depends on additive genetic variance which can be directly selected for.
What are some real-world examples of narrow sense heritability?
Narrow sense heritability has not been measured in any human traits. Traits in chickens can have high values for narrow sense heritability (such as weight), but not yolk weight. On a dry track, a controlled environment, most of the variation in
race-horse speed is due to genes, so value of h2 is high. But on a wet less controlled racecourse the value of h2 will reduce.
