Lecture 13 - Complex Traits

Question 1

What is genetic determinism?

Answer 1

Genetic determinism is the idea that genes solely determine physical characteristics or behaviours, ignoring environmental and other influences.

Question 2

Why is Mendelian inheritance insufficient to explain all genetic diversity?

Answer 2

Explains only a minority of phenotypes.
Most traits depend on multiple interacting genes.
Overemphasis on Mendelian inheritance can mislead understanding.

Question 3

What are penetrance and expressivity?

Answer 3

Penetrance: Proportion of individuals with a genotype showing the expected phenotype.

Expressivity: Degree to which a trait is expressed, influenced by genetic or environmental factors.

Question 4

How is eugenics related to genetic determinism?

Answer 4

Eugenics uses determinism to justify limiting reproduction to create a “fitter” population.
Historically associated with forced sterilisation and discrimination.

Question 5

What is the relationship between genetic determinism and racism?

Answer 5

Misconception: Shared phenotypes reflect deep genetic differences.
Reality: More diversity exists within populations than between them.

Question 6

What defines complex traits?

Answer 6

Governed by multiple loci and environmental factors.
Do not follow simple Mendelian inheritance.

Question 7

What is the difference between additive and non-additive gene action?

Answer 7

Additive: Alleles contribute fixed, cumulative effects to a phenotype.
Non-additive: Dominance or epistasis affects the phenotype unpredictably.

Question 8

What is heritability, and how is it measured?

Answer 8

Broad-sense heritability (H²): Proportion of phenotypic variance due to genetics.

Narrow-sense heritability (h²): Proportion of additive genetic variance that is inheritable.

Question 9

What are QTLs?

Answer 9

Quantitative Trait Loci (QTLs) are genomic regions controlling complex traits, identified through linkage between genotypic markers and phenotypes.

Question 10

What is GWAS, and what are its advantages?

Answer 10

Genome-Wide Association Studies (GWAS) identify genetic variants in natural populations.
No need for controlled crosses, applicable to humans.
Identifies narrow genomic regions associated with traits.

Question 11

What is linkage disequilibrium?

Answer 11

It measures how closely genetic variants are inherited together.
High linkage disequilibrium means little recombination between alleles at nearby loci.

Question 12

Why is Mendelian inheritance insufficient for teaching genetics?

Answer 12

It oversimplifies the diversity of inheritance.
Traits often involve multiple genes and environmental influences.
Can lead to misconceptions, such as “a gene for every trait.”

Question 13

What is the societal impact of genetic determinism?

Answer 13

It can lead to flawed ideologies like eugenics.
It promotes stereotypes, racism, and discrimination.
Fails to acknowledge the role of environmental factors in shaping traits.

Question 14

What are complex traits, and how do they differ from Mendelian traits?

Answer 14

Complex traits are influenced by multiple genes and environmental factors.
They display continuous variation (e.g., height, skin colour).
Inheritance often involves quantitative genetics.

Question 15

What is the role of QTL mapping?

Answer 15

Identifies regions of the genome associated with specific traits.
Uses controlled crosses to correlate genetic markers with phenotypes.
Helps locate traits influenced by multiple genes.

Question 16

How does lack of recombination affect QTL mapping?

Answer 16

Associated markers are physically close to the QTL.
These markers are inherited together with little recombination.
Fine mapping is needed to pinpoint the exact genetic locus.

Question 17

What are the pros and cons of GWAS?
(Genome Wide Association Studies)

Answer 17

Assesses many alleles in natural populations.
Useful for identifying common variants in a population.
Cons:
Requires large sample sizes for rare variants.
Detects only narrow genomic regions and common variants.

Question 18

What is the “missing heritability” problem?

Answer 18

Not all phenotypic variance can be explained by identified genetic variants.
Possible reasons: rare variants, undetected small-effect QTLs, or overestimation of narrow-sense heritability.

Question 19

What is pleiotropy, and how is it significant?

Answer 19

A single gene affects multiple phenotypic traits.
Example: APOE gene influences Alzheimer’s disease and cardiovascular conditions.

Question 20

How does genetic testing help understand complex traits?

Answer 20

Personal genomics identifies QTLs associated with traits.
Helps assess predisposition to diseases like Alzheimer’s.
Provides insights into heritability and trait risk.

Question 21

What are the ethical concerns of direct-to-consumer genetic tests?

Answer 21

Data may be sold to third parties.
Lack of proper counselling could lead to misinterpretation.
Law enforcement or insurance companies might access the data.

Question 22

What are the positive and negative aspects of knowing your genetic risks?

Answer 22

Positive: Enables preventive measures for some conditions.
Negative: Causes emotional burden for conditions without cures (e.g., Alzheimer’s).

Question 23

What is the difference between clinical genetic testing and direct-to-consumer tests?

Answer 23

Clinical testing: Doctor-guided, includes counselling and medical advice.

Direct-to-consumer testing: No medical oversight; results may lack context or interpretation.

Question 24

How does narrow-sense heritability (h²) differ from broad-sense heritability (H²)?

Answer 24

Narrow-sense heritability: Proportion of genetic variance due to additive effects, which can be inherited.

Broad-sense heritability: Includes all genetic components (additive, dominance, and epistasis).

Question 25

How does APOE genetic variation affect Alzheimer’s risk?

Answer 25

E4 allele: Increases risk significantly.
E2 allele: Reduces risk.
The additive effect of multiple E4 alleles sharply increases risk.

Question 26

What is the importance of additive genetic variance in selection?

Answer 26

Traits with high additive variance are more responsive to selection.
Breeding strategies aim to maximise additive genetic contributions for desired traits.

Question 27

Why are social responsibilities important when studying genetics?

Answer 27

Misinterpretations can reinforce harmful stereotypes and discrimination.
Ensuring ethical application of findings is critical for societal benefit.