Lecture 14 - Genetics, Epigenetics, Brain and Behaviour

Question 1

What does our unique behaviour profile arise from?

Answer 1

• Individual DNA sequence
• Env factors we are exposed to throughout life
• Complex interaction between both of the above

Question 2

How is DNA inherited?

Answer 2

• Via chromosomes
• Somatic cells contain 46 chromosomes but 23 in germ cells (sex)
• Split into autosomes and sex chromosomes
• XX = female, XY = male

Question 3

Where do polymorphisms occur?

Answer 3

• At a single base pair (1 in every 300) called SNP
• Larger chunks of DNA (deletion) called CNV

Question 4

What is a gene?

Answer 4

• A stretch of DNA that encodes a functional molecule
• Genes are transcribed into RNA molecules to be expressed

Question 5

What are the main parts of DNA?

Answer 5

• Exons are important and only make up 1-2% of DNA
• Junk DNA = regulatory DNA

Question 6

What happens to RNA?

Answer 6

• Retained in nucleus or can be transported
• mRNA are moved to ribosomes and translated to specific polypeptides to build a protein.

Question 7

What are the 4 types of proteins?

Answer 7

• Structural
• Catalytic
• Regulatory
• Receptors
• Transporter

Question 8

How do genes make different proteins?

Answer 8

• One gene can give slightly different transcripts (splice variants) to make slightly different proteins
• Complexity explains sophisticated brain functions (because of different methods of splicing)

Question 9

Why must DNA be read differently in different places?

Answer 9

• All cells of body have the same DNA
• Cells from different organs can be different
• Cell functions change over time because genes are switched on/off

Question 10

What is an example of why genes must be read differently in different places?

Answer 10

• STS is present in all cells
• Only being read in a certain part of the brain

Question 11

How is gene expression regulated?

Answer 11

• Extent to which RNA polymerase can bind to the start of the gene and continue along the DNA sequence
• To be packaged in the nucleus, DNA is wrapped about histone proteins
• Form chromosomes

Question 12

How do you chemically modify chromosomes?

Answer 12

• Acetylation & methylation affect accessibility of the DNA and gene expression
• Chemical modifications to DNA e.g adding stuff to it. Influences binding of RNA polymerase.
• Methylation blocks RNA polymerase to the start of the gene = not read/expressed

Question 13

What is epigenetic modifications?

Answer 13

• Reversible & dynamic
• Modulated by cells env
• Env can affect epigenetic markers affecting expression and function
• Inc. drugs, toxins/trauma, signalling molecules, stress, diet

Question 14

Describe the study on mice:

Answer 14

• Pregnant mice and gave some genistein which promotes methylation and others were given control
• Pups exposed to genistein looked different to control e.g darker and non-obese

Question 15

Study about environmental stresses:

Answer 15

• During the Dutch Hongerwinter and Chinese Famine
• Pregnant women gave birth to smaller babies with increased risk of obesity and schizophrenia
• Evidence of children’s DNA with more methylation.

Question 16

Study of epigenetics effecting offspring:

Answer 16

• Mice learnt smell of cherry blossom = electric shock
• Bred to naïve females and dads were killed so cant interact with pups
• Tested pups by exposing them to the smell
• Pups with dads that were scared were also scared of the smell
• Dads mark in sperm via epigenetic signatures = altered methylation. When inherited it affected structure of olfactory circuits in the brain and therefore interaction.

Question 17

How is our raising affecting epigenetics?

Answer 17

• Rat mums either lick/groom/nurse or the opposite
• Once pups grown up, the ones with nice mums had lower stress responses
• Looked at methylation in gene for stress response, and found different levels.
• If you swap the pup mums, the epigenetics reverse and methylation increases/decreases after birth

Question 18

How does epigenetic variation phenotypic variability over time?

Answer 18

• MZ twins are more alike earlier in life
• Study examined epigenetic markers across the genome at two timepoints to see whether changes in time can explain increased phenotypic divergence

Question 19

What is evidence for an interaction between genes and the env?

Answer 19

• Longitudinal study
• Looking at serotonin and depression
• Gene making transporter comes in two versions (long/short alleles)
• There is a known relationship between stressful life and likelihood of depression
• Results show no stressful life events = genetics don’t matter, but stressful life events = more likely for depressive symptoms. L/L = less vulnerable, S/S = more vulnerable

Question 20

What are polymorphisms?

Answer 20

• Slight variations between individuals at particular genomic sites
• Affect DNA function = individual differences