Behavioural Genetics

Question 1

What are the four types of nucleotides (bases) that make up a DNA polymer?

Answer 1

Thymine(T), Adenine(A), Guanine(G), and Cytosine(C)

Question 2

Describe a DNA molecule

Answer 2

Two strands of nucleotides running in opposite directions, coiled into a double-helix.
Nucleotides from each strand are held together by hydrogen bonds

Question 3

What are the specific pairs that nucleotides can form bonds in?

Answer 3

T - A or A - T

C - G or G - C

Question 4

What is being referred to by ‘the sequence’

Answer 4

The order nucleotides are found along the strand

- very important for DNA coding

Question 5

How many chromosomes do humans have?

Answer 5

23 pairs

46 in total

Question 6

How do mutations in DNA occur?

Answer 6

A cell divides, the DNA helix is ‘unzipped’ so a complimentary strand can be made.
Sometimes errors are made when the new strand is made, so it isn’t identical.
If a repair enzyme does not fix this error, a mutation occurs

Question 7

Name the three ways DNA mutations can occur

Answer 7

1. Base-pair substitution
   - one nucleotide and its partner are replaced by a different pair
2. Deletion
   - the loss of one or more base pairs
3. Insertion
   - the addition of one or more extra base pairs

Question 8

What is RNA?

Answer 8

Ribonucleic acid

- single strand chemical that can serve as a template for the synthesis of proteins

Question 9

What is the name of the process that creates RNA from DNA?

Answer 9

Transcription

Question 10

What are the nucleotides found in RNA?

Answer 10

Uracil (replaces thymine)
Adenine
Guanine
Cytosine

Question 11

What is mRNA?

Answer 11

Messenger ribonucleic acid

• is essentially a disposable copy of a gene
• carries the protein building information (codons)

Question 12

What does mRNA do?

Answer 12

Translation

• carries protein-building message that is encoded by sets of genetic words which occur one after another along the length of DNA
• decodes protein-building information
• results in a polypeptide chain

Question 13

What is a codon?

Answer 13

The protein building information carried by mRNA

• they are 3 bases long (e.g. A-C-G)
• there are 64 codons
• each codon refers to a specific amino acid

Question 14

How many base pairs (nucleotide pairs) are there in a human chromosome?

Answer 14

50,000,000 - 300,000,000

Question 15

What is a gene?

Answer 15

A segment of a chromosome

Question 16

What is a homozygous gene?

Answer 16

An identical pair of alleles on the two chromosome

a base pair that is made up of the same base twice e.g. TT

Question 17

What is a heterozygous gene?

Answer 17

A pair of alleles on the two chromosomes that are different (a base pair made up of two different nucleotides e.g. TA)

Question 18

What is epigenetics the study of?

Answer 18

How your behaviour and environment can cause changes that affect the way your genes work

• e.g. some genes are only active at a certain point in one’s life
• changes are reversible and do not alter DNA sequence

Question 19

What is a dominant gene?

Answer 19

A variant of a gene that expresses itself more strongly than any other version of the gene which the person is carrying
Shows a strong effect in both the homozygous and heterozygous condition

Question 20

What is a recessive gene?

Answer 20

A gene who’s effects are hidden in the presence of a dominant gene
It will only show its effect in the homozygous condition (if there are two bases the same)

Question 21

What is PER?

Answer 21

A protein produced by period genes, that promotes inactivity and sleep

Question 22

What is TIM?

Answer 22

A protein produced by timeless genes, that promotes inactivity and sleep

Question 23

What happens to the concentrations of PER and TIM throughout the day?

Answer 23

They oscillate

• synthesis of PER and TIM are very low at sunrise but increase throughout the day
• levels of the proteins themselves then increases later in the day, so PER&TIM levels are high at night

Question 24

What is Familial advanced sleep disorder (ASPD)?

Answer 24

A Circadian Rhythm Sleep Disorder
A mutation in the Per2 gene, that causes persistent advanced onset of sleep and awakening
- sufferers typically experience sleepiness in the early evenings rather than later on (at night)

Question 25

What is a proband?

Answer 25

A person serving as the starting point for a genetic study of a family

Question 26

How was Familial advanced sleep disorder (ASPD) discovered?

Answer 26

- Proband's sleep phase was brought forward 4-8 hours - Proband participated in time-isolation experiment for 3 weeks (stayed in an environment with no time cues) - showed a 1 hour shortening in her circadian period - a mutation in the Per2 gene was identified

Question 27

What are Familial natural short sleepers (FNSS)?

Answer 27

Circadian Rhythm Sleep Disorder - People with mutation in the DEC2 gene - Carriers needed only 6 hours of sleep a day - mutation leads to difference in EEG architecture of sleep (higher delta power during slow-wave NREM & less REM sleep)

Question 28

What is Brain-Derived Neurotrophic Factor (BDNF)?

Answer 28

A neurotrophin, important in neurogenesis and plasticity

Question 29

What is Heritability?

Answer 29

Refers to how much characteristics depend on genetic differences

Question 30

What can change the impact of genetic influences (heritable genes)?

Answer 30

Strong environmental influences can cause genetic influences to have less of an impact

Question 31

How do genes affect our behaviour?

Answer 31

- They do not directly produce behaviours - Genes produce proteins that increase the probability that a behaviour will develop under certain circumstances - Genes can also have an indirect effect - can alter your environment by producing behaviours or traits that alter how people in your environment react to you

Question 32

What is the most common twin-model used in twin research to explain the amount of variance between twin pairs?

Answer 32

The ACE model: - A (or h2) = Additive genetic effect. This is the proportion of variance of a phenotype explained by genetic influences - C = Common environmental influences (proportion of the variance of a phenotype explained by shared environment) - E = Non-shared environmental influences, unique to each twin (proportion of the variance of a phenotype explained by a non-shared environment)

Question 33

What are some examples of Non-Shared Environmental factors for children growing up in the same family?

Answer 33

Peers Child-specific illnesses / events Events occurring to an individual

Question 34

What are some examples of Shared Environmental factors for children growing up in the same family?

Answer 34

Socioeconomic status Characteristics of the home e.g. number of books in home Parenting less likely to be shared - can't be treated in exactly same way

Question 35

What is the Univariate twin model?

Answer 35

Asks how much of the variance (between twins) in a trait is explained by A, C or E from the ACE model?

Question 36

What is the Bivariate twin model?

Answer 36

Asks to what extent is trait 1 caused by the same genetic and environmental influences as trait 2

Question 37

What is Genetic Correlation?

Answer 37

Is independent of the phenotypic relationship between two traits Is independent of the heritability estimates of either trait

Question 38

What are the Pros of twin studies?

Answer 38

- All Ps are same age - Can partition variance into A + C + E - Reasonably representative of general population - Don't need a control group

Question 39

What are the Cons of twin studies?

Answer 39

- Requires large samples (>1000 pairs) to have sufficient power - Design has many assumptions - Some twin-specific characteristics are not generalisable to singletons

Question 40

What are the assumptions of twin studies?

Answer 40

- Findings from twins are generalisable to singletons - Assumes no gene-environment correlation or interaction - Equal environments assumption: assumes environmental influences are equivalent for MZ and DZ pairs