PSYC - Week 3: Genetics and Evolution

What are Chromosomes?

are long strings of DNA wrapped around a specific protein (called Histones)

Where are chromosomes found?

nucleus

How is our genetic material sorted from parents?

half and half

How many pairs of chromosomes do we have?

23 pairs

What are the pairs of the four nitrogenous building blocks that make up the genetic code?

Adenine & Thymine, Cytosine & Guanine

What is a phenotype?

set of observable characteristics or traits

Homozygous vs. Heterozygous

an organism with two identical alleles for a specific gene.

an organism with two different alleles for a specific gene. (one is dominant)

Can 3-point shooting be determined by just one gene?

no, it is influenced by multiple genes and environmental factors.

Nature and Nurture refer to what?

Nature = genes and Nurture = Environment

What is the percentage of variability in alleles across people?

only 0.5%. 99.5% of alleles are the SAME across all people.

Behavioural Genetics

The empirical science of how genes and environments combine to generate behaviour.

Quantitative Genetics

Using scientific and mathematical methods to understand how genetics (nature) and environment (nurture) influence traits by comparing similarities and differences between individuals.

Heritability Coefficient

misinterpreted statistical idea that refers to measure the role of genetics in the explanation of differences among individuals.

A number between 0 and 1 that estimates how much of the variation in a trait within a population is explained by genetic differences.

What are Histones?

are groups of proteins (8) that package and order DNA into structural units called nucleosomes, playing a crucial role in gene regulation and chromatin structure.

Epigenetics

Epigenetics is the study of changes that control whether genes are turned ON or OFF without changing the actual DNA sequence. These changes can happen through chemical modifications to DNA or histones.

Genotype

The genetic information you inherit from your parents.

Genotype + Environment →

Phenotype

DNA methylation

is an epigenetic mechanism that involves the addition of a methyl group to DNA, affecting gene expression without altering the DNA sequence (Covalent modifications) occurring via the methylation of cytosine.

Histone modifications

Posttranslational modifications of histones are chemical changes made to histone proteins after they are produced.

These changes can:

• Loosen or tighten DNA around histones, affecting chromatin structure.

• Turn genes on or off by making DNA more or less accessible.

• Attract proteins that help control gene expression.

What is Acetylation?

• DNA is wrapped around proteins called histones.

• Adding acetyl groups to histones usually makes the DNA less tightly wrapped.

• This makes the DNA more accessible, so genes are generally more likely to be expressed (turned on).

Acetylation → loosens DNA → genes more accessible → increased gene expression

Epigenome

The epigenome is a collection of chemical modifications to DNA and histone proteins that help control which genes are turned on or off without changing the DNA sequence.

= when chemical tags get added to histones or directly to DNA, and then the chromatin loosens or tightens. That changes whether the gene in that area is easy for the cell to use or not. So it's like a switch or a dial on gene activity.

How does Epigenetic marks affect identical twins?

Epigenetic marks can lead to differences in gene expression, resulting in varied traits and behaviors despite identical DNA.

Nature X Nurture

Genes interacting with the environment

Natural Selection

Differential reproductive success as a consequence of differences in heritable attributes.

Sexual Selection

The evolution of characteristics because of the mating advantage they give organisms

Adaptations

Evolved solutions to problems that historically contributed to reproductive success.

How can sexual selection be categorized?

Inter-sexual competition: When individuals compete to be chosen as a mate by the opposite sex, often by displaying attractive traits.

Example: A male peacock displaying colourful feathers to attract a female.

Intra-sexual competition: When individuals of the same sex compete against each other for access to mates.

Example: Two male deer fighting for the opportunity to mate with a female.

How would someone’s upbringing and environment influence their ability to handle stress?

Your environment can cause chemical changes that affect whether certain genes are more or less active, without changing the actual DNA sequence.

If DNA is tightly packed → harder to access → genes are generally _______ expressed.

less

If DNA is more loosely packed → easier to access → genes are generally ______ expressed.

more

Histones have a ________ charge, while DNA is _______ charged.

positive & negatively - this means they attract each other and allows DNA to tightly wrap around the histone.

What needs to happen for this process to occur?

reduces the positive charge of histones → DNA is held less tightly → chromatin loosens

Histone acetylation - acetyl groups added

DNA methylation → gene tends to be turned __________

down or off

What is the difference between intuition and scientific evidence when studying nature vs. nurture?

• Intuition: What people believe about whether a trait is inherited (nature) or learned (nurture).

• Scientific evidence: Uses research and data to determine how genetics and the environment influence traits.

Key idea: Just because a trait seems innate or learned doesn't mean it is. Most traits are influenced by both nature and nurture.

Why is it harder to have studies with humans?

Unlike animal studies, experiments with humans face ethical and practical issues in assigning parents or controlling their environments. 

What are Monozygotic (MZ) Twins? What are Dizygotic (DZ) Twins?

MZ: Identical twins sharing 100% of DNA. Potentially revealing strong inheritance of traits. 

DZ: Fraternal twins sharing 50% of DNA. Useful for comparing environmental versus genetic influences. 

What are Quantitative Genetics?

Examines genetic influence across various relationships and traits through measures such as heritability coefficients. 

=The study of how genes and environment influence differences in traits, often measured with heritability.

Evolution

Change over time wherein traits and behaviors develop due to their advantages in survival and reproduction.

Survival adaptations

Aid in surviving environmental challenges (e.g., sweat glands for temperature regulation).

Reproductive adaptations

Enhance chances of successful mating (e.g., attractive traits that appeal to potential mates). 

Individual Fitness

Success of genes that enhance the reproductive odds of an organism. 

Inclusive Fitness

Helping relatives survive can also promote the replication of shared genes. 

Evolutionary Psychology 

A framework that connects evolutionary theory with modern psychology, concentrating on psychological adaptations. 

Psychological Adaptations

Changes in the mind designed to address specific survival or reproduction challenges. (food preferences, social interaction tendencies)

Sexual Strategies Theory

explains differences in mating strategies based on parental investments: Women: tend to value resources and commitment.

Men: tend to value youth and health as signs of fertility.

Error Management Theory (EMT)

Error management theory says our brains evolved to avoid the most costly mistakes in uncertain situations. So we accept smaller, less costly errors instead.

Ex. A visual descent illusion - overestimation of heights to avoid falls.

Ex. B: Sexual overperception bias—men often overestimate signs of sexual interest from women, potentially maximizing reproductive opportunities. 

Cultural Influences

Evolution has shaped our psychological tendencies, but culture and social environments influence how these tendencies are expressed.

 

Modern Implications

Understanding evolutionary influences on behavior helps in addressing contemporary issues in relationships, societal norms, and individual behaviors. 

Genome

The DNA sequence

Phenotypic plasticity

the ability of one genotype to produce different physical, physiological, or behavioural outcomes depending on the environment.

More DNA methylation → ______ gene expression 

less

What do HATs (histone acetyltransferases) do?

Add acetyl groups to histone proteins, loosening DNA around histones and making genes more accessible for transcription.

What do HDACs (histone deacetylases) do?

Remove acetyl groups from histone proteins, causing DNA to wrap more tightly around histones and generally reducing gene expression.