6. Genetics Flashcards
(21 cards)
What is the human genome?
The complete set of nucleic acid sequences encoded as DNA in humans
Organized into 23 chromosome pairs (46 total chromosomes)
Comprises approximately 3 billion base pairs
How similar is the human genome across individuals, and what portion explains our differences?
Humans share > 99% identical DNA sequence
The remaining < 1% variation underlies individual differences in physical and psychological traits
What are alleles, and how do they influence protein function?
Alleles: Alternative versions of the same gene
Different alleles can lead to:
Altered protein shape (affecting function)
Changed protein quantity (affecting expression level)
What are the three main scales of genetic variation in the human genome?
Large scale:
Whole-chromosome number changes (e.g., trisomy)
Partial rearrangements (e.g., translocations, inversions)
Medium scale:
Copy number variations (CNVs)
Insertions and deletions of DNA segments
Small scale:
Single nucleotide polymorphisms (SNPs): single-base substitutions
why do we think genes may influence individual differences in complex traits/behaviours
Twin studies, adoption studies, molecular genetic studies
-Twin studies don’t tell you about the actual genes involved, but the genetic influences which account for variance on a trait
- Identical twins – share all of their varying DNA
> Monozygotic (MZ) twins look more similar to each other -> higher intraclass correlations than dizygotic (DZ) twins. DZ twins are about half.
> Applies to measures of cognitive development / psychiatric traits.
- Non-identical twins – share 50% of their DNA
Heritability
- a measure of the extent to which differences in people’s genes account for differences in their traits
- Heritability estimates derived from twin studies, are the sum total of all genetic variation
- Including ‘de novo’ mutations – i.e. genetic effects that are not necessarily inherited from parents
- Heritability estimates do not apply to a single individual:
> If a trait is 45% heritable, it means that 45% of individual differences in that trait are accounted for by genetic differences between individuals
> It DOESN’T MEAN that there is a 45% probability of a particular trait for a single individual
What did Langström et al. (2010) find about the heritability of same-sex sexual behavior?
Heritability estimate: ~20–40% in Western twin samples
Interpretation:
- 20–40% of variance in same-sex behaviour across individuals is due to genetic differences
Clarification: This is not the probability for any one person to be gay
Remaining variance: Attributable to individual-specific environmental factors (including biological ones like prenatal hormones)
Note: Simple heritability doesn’t capture gene–environment interplay
Why haven’t molecular studies matched twin-study heritability estimates for sexual orientation?
Missing heritability: Identified genetic variants explain less variance than twin estimates predict
Polygenic architecture: Many genes each exert very small effects
Implication: Enormous sample sizes needed to detect these small-effect variants
What were the key findings of Ganna et al. (2019) on same-sex sexual behavior?
Highly complex genetics: No single “gay gene”
Additive effects: Many genome-wide variants each contribute a tiny amount
Sex overlap: Some shared, some sex-specific variants
Examples in men: Variants linked to olfaction genes and androgen sensitivity
Prediction: Genetic predisposition cannot reliably predict an individual’s orientation
Do genetics support a single continuum (Kinsey scale) from opposite-sex to same-sex preference?
Genetic evidence: No single dimension underlies sexual orientation
Interpretation: Orientation likely reflects multiple, independent genetic and environmental influences rather than one linear scale
What do genetic studies tell us about gender identity?
Heritability: Twin and family studies suggest moderate to strong genetic influence
Molecular data: No robust gene-level findings yet
Environmental factors: Poorly understood—could include prenatal hormones as well as social experiences
Ethical considerations of genetic considerations into human sexual orientation and gender identity.
- behavioural genetics: is the science robust
- Depends on the trait that has been studied
- Many findings more robustly replicated in the field of behavioural genetics than in other fields
- Problem with lack of diversity in populations that have been studied
- Lack of diversity among researchers…
- Depends on the trait that has been studied
- fear of eugenics, discrimination and stigma, medicalisation, changing and selecting traits, impact on legal system etc.
Eugenics/ ‘well born’
- Eugenics (“well born”) is the idea that humanity can be improved using selective breeding
- Murky past of behavioural genetics
- Eugenics movement linked to the establishment of behavioural genetics as a field
- Founders racist
Effects of ‘active’ eugenics.
early 1900s: “Positive” eugenics – designed to increase fertility of those deemed to be fit; Negative eugenics – designed to decrease fertility of those deemed to be unfit
1920s+30s: compulsory sterilisation of the unfit in some countries; Nazi Germany selective breeding of racially pure, killing of children and adults in institutions
1960s: Continued sterilisation on eugenic grounds in some countries (e.g. Canada and Sweden)
Passive Eugenics
- Policies not designed to actively discourage reproduction, but are in favour of maintaining a particular ‘status quo’
- E.g. cis-women are the ones who carry a child and give birth
Fundamental problem with eugenics
- Fails to acknowledge the pluralism of values and is overly optimistic about our status as ‘designers’
- Eugenics is often based on a limited number of people’s beliefs and attitudes about ‘better people’, as well as limited and biased data
- Selecting for one trait may reduce fitness in other areas
- Genetics of complex traits probabilistic, not deterministic
- Violations of reproductive freedoms
- This has occurred in the past (e.g. Sweden)
What historical and conceptual concerns prompt calls to stop behavioural‐genetics research?
Eugenics legacy: Misuse of genetic ideas to justify discrimination and forced sterilisations
Genetic determinism: Fears that traits will be seen as “fixed” and used to “blame biology”
Misapplication: Risk that findings could underpin coercive “biological solutions” (e.g., conversion therapies)
What do we actually know about genetic influences on behaviour?
Probabilistic not absolute: Genes shift likelihoods; environment also shapes outcomes
Heritability confusion: Heritability estimates are about populations, not individual certainty
Gene–environment interplay: Simple models ignore how genes and environment interact over time
What are the main ethical concerns around modifying genetically influenced traits?
Preemptive modification: Fear of using genetic info to “tweak” behaviour or personality
Gene therapy overreach: Gene editing for complex, multifactorial traits lacks scientific support and poses risks
Prenatal selection:
PND/PGD acceptable for serious monogenic diseases (high predictive certainty)
Unacceptable for normal‐range traits (low predictive value, ethical “slippery slope”)
How should researchers guard against misuse when studying behavioural genetics?
Transparent aims: Publish clear rationales—aim to understand or treat, not “enhance” or “improve” traits
Inclusive teams & fair funding: Ensure diversity among investigators and equitable access to research leadership
Community engagement: Involve stakeholders, ethicists, and affected groups in setting priorities
What best practices ensure ethical communication and oversight of behavioural‐genetics research?
Responsible reporting: Emphasise probabilistic nature of findings; avoid “gene for X” headlines
Robust review: Ethics boards evaluate potential harms, especially around selection technologies
Data governance: Protect against data misuse, reidentification, or discriminatory applications
