Task 2

Question 1

What are Mendel’s 3 Laws?

Answer 1

1. Law of independent assortment:
   - genes/alleles are inherited individually and which characteristics of one parent end up in the childrens’ DNA is thus a product of chance.
2. Law of segregation:
   - During production of gametes, the two copies of each hereditary factor segregate, so that the offspring inherits one factor from each parent.
3. Law of Dominance:
   - One factor in a pair of traits dominates the other in inheritance unless both factors in the pair are recessive

Question 2

There are two types of allele configurations. What are they called?

Answer 2

Heterozygous; Homozygous

Question 3

What is a reason for the success of Mendel’s study with peas when looking at his research design?

Answer 3

He studied single-gene traits. With polygenetic traits, the results would have been less clear.

Question 4

What is linkage and what is its effect?

Answer 4

Genes with linkage are located at proximate loci on the genome and tend to travel together through generations.

Question 5

Why do Mendel’s laws support Darwin’s theory?

Answer 5

Because they solve the dilution problem. The laws show that offspring isn’t just a mixture of the parents, but dominance effects change how alleles are inherited. Thus evolution is about the survival of alleles and not necessarily about phenotypic traits.

Question 6

Explain how heritability is needed for evolution to function.

Answer 6

If there was no heritability, so genetic variation would only be explained by the environment, then certain traits would still increase the reproductive success of an individual. However in this case, this individual wouldn’t pass on its alleles, since there is no inheritance. Thus, evolution would never make progress, because every generation, the phenotypic traits are distributed by complete chance again.

Question 7

Why are some traits distributed on a curve?

Answer 7

• Most of these traits are polygenic
• By applying the probability laws of the Punnett Square, we can see that the expression of traits that depend on multiple genes will be distributed normally across the population.

Question 8

What is the liability threshold model?

Answer 8

The model of classifying people as having or not having a disease. (All or nothing) This is done based on a certain threshold, even though the disease (like with many mental illnesses) may be on a continuous scale.

Question 9

Humans are diploids. What does this mean?

Answer 9

It means that we have two copies of each gene (23 pairs = 46 chromosomes)

Question 10

Define Heritability

Answer 10

Ratio of phenotypic difference between two individuals, that can be explained by differences in their genome.
- Heritability is about the population as a whole and not individuals.

Question 11

Describe Mendelian Diseases

Answer 11

• Rare class of diseases as the host often dies before reproducing
• Two ways how these diseases spread:
  1. Phenotypic Effect occurs after the host has reproduced
  2. The disease allele is recessive
  (Also a reason to avoid inbreeding)

Question 12

What is the norm of characteristic?

Answer 12

If two people are genetically identical, but differ in phenotype, this difference can be referred to as the “Norm of Characteristic”.

Question 13

What is the Hardy Weinberg Equilibrium and which questions does it answer?

Answer 13

• A theoretical, mathematical scenario, that answers the questions
  1. if overall allele frequencies change over generations.
  2. if there will be in imbalance between homozygous and heterozygous individuals in the future.

Question 14

What are the necessary assumptions to apply the Hardy Weinberg Equilibrium?

Answer 14

• Population is diploid
• Infinite population size
• sexual reproduction
• no selection -> Everybody has the same chance of reproducing

Question 15

Describe the math behind the H-W-Equilibrium

Answer 15

p = frequency of allele A; q = freq. of allele a
P(AA) = p² ; P(Aa) = 2pq

Proportion of the next generation receiving A:
p² + 0.5(2pq) = p² + pq = p²+p*(1-p) = p²+p-p² = p

• > Proportions stay the same
• > If the math doesn’t add up, then there is evolution

Question 16

If the H-W-Equilibrium doesn’t add up, then allele ratios change over generations. What is the technical term for this?

Answer 16

Genetic Drift

Question 17

What is “Fixation”?

Answer 17

When an allele is present in everyone in a population.

Probability of fixation is ca.: 1/2N

Question 18

What does the Natural Theory of Molecular Evolution by Kimura (1983) say?

Answer 18

That larger population undergo more mutation, but mutations become common less quickly and these effects cancel each other out.

Question 19

What is the idea of the “Molecular Clock”?

Answer 19

Establishing the time since two populations last common ancestor based on their genetic difference.

Question 20

We refer to it as pleiotropy, if:

Answer 20

One has an effect on multiple phenotypic traits.

Question 21

Define the coefficient of relatedness (r)

Answer 21

Probability that any particular allele in an individual is identical by descent as the allele in another person.
In other words: The proportion of shared genes.
-> For siblings and parents: 0.5
-> You are the “index case”

Question 22

Which study design can be used to find about the effects of epigenetic factors?

Answer 22

• Twin Studies

- Adoption Studies

Question 23

What are the properties and weaknesses of twin studies?

Answer 23

• Twins often grow up in very similar environments -> Eliminates this variable.
• With this study design, we can infer on all factors: A,C & E
• We then compare the phenotypic differences between Monozygotic and Dizygotic twins
• > Falconer’s Estimate of Heritability = [Corr.(MZ) - Corr.(DZ)]*2
• Results: A is substantial in most traits; C tends to be less important than E

Problem:
- Environment might differ between twins

Question 24

Describe the factors in the ACE Model.

Answer 24

A = Heritability
C = Shared Environment
E = Non-shared Environment

Question 25

What are the properties of adoption studies?

Answer 25

• Provide a good estimate of the relative strengths of A and C, if the adopted child was adopted at a young age and is about equally as old as the biological child
• C seemed to have a relatively small impact

Problems:

• Parent/Child selection process could lead to an overestimation of C factor
• C could be underestimated since prenatal development is dependent on the biological mother and not the adopting parent.

Question 26

When a gene A effects the expression of another gene, this is called…

Answer 26

Epistasis

• > Dominant Epistasis: Dominant allele in A effects the expression of gene B
• > Recessive Epistasis: Gene A effects he expression of B only if it comes in the aa-form

Question 27

Why do some scientists prefer the measure of “Coefficient of Additive Genetive Variance (CVA)” over Heritability?

Answer 27

Because it is a total measure rather than a proportion. In proportions the effect of one factor goes down as the effect of other factors goes up, even though this is factually not the case.

Question 28

Why are Gene wide Association Studies gaining more popularity?

Answer 28

It’s getting cheaper.

Question 29

What are the top 10 findings from the Article?

Answer 29

1. All psychological traits show great genetic influence
2. No traits are 100% heritable
3. Heritability is caused by many genes with small effects.
4. Phenotypic correlations between psychological traits also show significant genetic covariance.
5. The factor “heritability” of intelligence increases throughout development.
6. Age to age stability of traits is often due to genetics.
7. Most measures of “Environment” show great genetic influence.
8. Most associations between environmental measures and psychological traits are significantly mediated by genetics.
9. Non-shared environment is mostly more influential than shared.
10. “Abnormal is normal” -> Normal distribution

Question 30

What is the difference between Non-sense Mutations and Missense Mutations?

Answer 30

Non-Sense Mutations change the RNA sequence in a way that leads to termination of the translation progress.

Missense Mutations result in a different amino acid.