LECTURE 12 (Quantitative Loci) Flashcards
What’s quantitative genetics?
traits that are more complex than monogenic or oligogenic because they have environmental component as well
The phenotypes are determined by which two things?
environmental variation and phenotypic variation
What are the main types of traits?
- continuous e.g height, weight
- non continuous ; meristic: countable e.g number of denticles in a drosophila larvae and threshold; either have it or don’t have it (if you don’t then you0re over the threshold)
What are quantitative traits determined by?
many genes that act independently (not related) + environmental effects
Can the phenotype/ genotype be predicted with quantitative traits?
no, because the environment has an effect on them.
what’s quantitative genetics?
the study of quantitative traits which are continuously varying characters
What does the polygenic theory involves?
it states that certain traits are produced due to the cumulative effect of several genes (assumes that genes are additive)
what if environmental variation is added to polygenic theory?
then we start to see much more variation of phenotypes
what states the number of phenotypes in the polygenic theory?
the genes
pheny= 2n + 1 being n the number of genes acting
give an example of polygenic inheritance of traits.
pigmentation in plants, if there’re two bialletlic genes A and B, there will be 5 phenotypes due to additive gene action. everything is based in units of color. big alleles contribute 2 + 1/4 and small contribute 1/4 of units of color
AaBa will have 5 units of color the phenotype is determined by the number of units of color
What are the two parameters that describe normal distribution?
- standard deviation and variance.
What are the main components of phenotypic variation in quantitative traits?
Vp= Ve (environmental) + Vg (genotipic)
how can we calculate Ve or Vg?
we make the other one 0.
Ve: individuals of uniform genotypes (Vg) grow in different environments
Vg: individuals of the same environmental conditions show different genotypes
What are the main components of genotypic variation?
Va: additive variation
Vd: dominance genetic variance
Vi: epistatic or interaction genetic variance.
What’s additive variation? (Va)
sum of phenotypic effects of alleles when assembled in the genotype
what do we inherit from parents, alleles or genotypes?
WE INHERIT ALLELES
what is the dominance genetic variance (Vd)?
it’s the deviation from the genotypic values due to additive gene action due to dominance (dominance of one genes over other)
what is the epistatic or interaction genetic variance (Vi)?
the deviation from the genotypic values due to additive gene action between loci
What are the main components of environmental variation?
- unkonw causes
- spatial (env space)
- temporal (time)
- maternal (e.g nutrition)
is the genotype independent from the environment?
no, GXE INTERACTION.
explain the three types of gene environment interaction.
paper: 5 groups of varying level of a trait different categories of env. - additive: no G-env interaction - fan-shaped - cross-over.
what’s phenotypic plasticity?
phenotypic variation due to genotypic variation in response to the environment
with the example of drosophila from the lecture, explain the effect of N.S on different traits and why is that.
N.S acts on traits related to reproductive outputs e.g eggs and ovary , additive genetic variance is lower for these traits because because N.S will increase favorable alleles, the dominant ones so Vd and Vi are higher.
what is broad sense heritability?
proportion of phenotypic variation attributable to genetic effects (variation in genotype)
e.g if 61% it means that 61% of the variation in phenotype is due to variation in genotype
what is narrow sense heritability?
phenotypic variation attributable to the sum of phenotypic effects of alleles when assembled in genotypes
How’s heritability measured?
it’s measured in a population not in one individual
it’s measured by comparing relatives and by artificial selection?
What’s covariance?
when you compare different relatives and see the amount of gene they share.
How’s covariance used to measure heritability?
looking at the strength of covariance look at the parents mid value and offspring mid value and compare those in relation to covariance. this can be done with different families and produce an scatterplot the slope of the line is the heritability if it’s done with only one parent the slope is half the heritability
how can we test the relatedness between two individuals?
IBD: n (0.5)^i
n= number of routes
i= number of meiosis
how can we know the number of routes?
you always need to go back to the most common ancestor.
difference between monozygous and dizygous twins.
MZ: come from same egg share all genes
DZ: come from different eggs share half of the genes
How can we test two twins for the presence absence of a disease?
use the concordance rate.
What’s the concordance rate of twins?
CR: the P(that twins) will have certain characteristic both
How does CR varies bt MZ and DZ twins?
MZ CR> DZ CR
give an example of distinct CR of a disease
CF 100% CR MZ and 25% CR DZ
how can we compare MZ AND DZ TWINS for continuous characters rather than non-continuos.
we use the correlation coefficient (r)
How does r vary bt MZ and DZ twins?
Mz r> DZ r
what’s the main problem with twin studies?
they never have exactly same env, teachers and parents treat them differently
