review of test questions with answers
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1. Define heritability using mathematical model and explain the scientific definition as
•Heritability is defined as the ratio of genotypic variance (Vg) to the phenotypic
variance (Vp) of a particular trait.
•It can be defined using the following formula:
h2 = VG / (VE + VG) , where VG is the genetic variance and VE is the
environmental variance and VP = VE + VG, where VP is the phenotypic
•Therefore, if genetic analysis found that heritability of losing an eye is 0% then it
can be said that in a population 0% of the variation is in the population for this
trait will be based on genetics. i.e. 100% of variation is based on the environment.
2. What does it mean when heritability is 0%?
•It means that 0% of the variability observed in a population is based on genetic
factors that is to say 100% of the variability is due to environmental factors.
•This make sense, assuming that genetically all individuals are born with 2 eyes but
due to some environmental effects some lose 1 eye or both.
For ex: in a population, every year grade 3 kids have a snowball fight with
each other, with half of them getting one eye knocked out.
•Genetically, they all had eyes but due to environmental effects half of them lost
one eye. This means that the variability seen in the population for 3rd grade for this
trait is based on environmental effects not genetic factors.
•This implies that relative importance of genes for the trait of losing an eye is
negligible as genetically everyone is born with eyes.
•However, the environmental effects on this trait determine the variability found in
•Genetic variance (Vg) is zero because this trait is so important that natural
selection has selected against any variation.
3. Give a real or hypothetical example where heritability equals 100%. Explain how
this would be possible and what this would mean in terms of environmental and
•If we assume that the heritability of IQ is 100%( hypothetically) then,
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In a population, with a homogeneous environment for every individual,
100% of the variability in IQ found in the population will be based on
This means that variations in the population will be based entirely in
•However, this does not mean that the environmental effect is negligible. If the
environment effect for half of the population changes then heritability value is not
valid. Also the population in a homogeneously poor environment may have an
overall average IQ that is lower than that of population that is in rich environment.
Thus, the environmental effect is important for the overall average IQ of
population but not for the variation found in the population for that trait.
•In order for heritability of IQ to be 100% or any trait to be 100%, natural selection
must have selected for that trait to be variable based on genetic effects.
4. The comparison of major racial groups with regard to their performance on IQ tests
is problematic and potentially why the test results are flawed. Circle the right
•Major racial groups are not genetically well defined
•Larger genetic variability within as compared to between racial groups
•Phenotypical recording techniques are biased (IQ test)
•Environmental effects are not parsed out
•Heritability estimates are incorrect therefore
•But even if they were correct, interpretation, “spending money on social programs
is a waste” is wrong:
•Genes do not have deterministic effects.
•If we know about their effects and if we study how they exert them, then we can
design “environmental” programs to circumvent, augment, improve on their
5. An experimenter decided to test three different mouse strains A(CD1), B(C57BL6),
and C(DBA/2) in 7 different environmental conditions and analyzed the learning
capacity of these mice in these 7 test situations. Explain whether her results
demonstrate the presence and/or absence of genotype x environment interaction.
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