Discuss the threshold model and what the implication is on complex traits
Complex traits are traits controlled by multiple genes and where there is interaction between the
genes and the environment. The genes controlling the trait act additively, contributing to the
phenotype. To look for the threshold effect, the frequency of the disorder among relatives of
affected individuals is compared with the frequency of the disorder in the general population. Risk of
developing the disorder should decrease with decrease in degree of relatedness (first degree
relatives have half their genes in common, second degree relatives a quarter, etc.)
A threshold exists above which the abnormal phenotype is expressed.
Explain how the number of loci contributing to a trait, also contributes to continuous variation.
Continuous variation is the distribution of phenotypic characteristics from one extreme to another in
an overlapping and continuous fashion, thus showing a lot of variation. If there are multiple loci
contributing, it would produce more phenotypic ‘classes'. Also, environmental variation will lead to
more phenotypic variation through GEI and GEC
How can the significance of QTL contributing to a phenotype be determined?
To determine which candidate gene(s) in an interval containing the QTL actually correspond to the
QTL include:
Identifying potentially functional DNA polymorphisms between alternative alleles of one of the
candidate genes
Observing a difference in mRNA expression levels between homozygous genotypes
Observing expression of RNA or protein in tissues thought to be relevant to the trait
Observing failure of a mutation in the candidate gene to complement the QTL
Observing that a mutant allele of the candidate gene affects the behaviour
For association studies: independent replication of the association
Explain behavioural plasticity by referring to the epigenetic landscape.
Epigenetics is the change in phenotype without changing the DNA sequence, by changing gene
expression through DNA methylation or histone modification. Your genotype determines the
boundaries of phenotypical variation, and epigenetics controls the variation within those
boundaries.
, DNA methylation is when methyl groups are added to certain bases to repress gene activity. Histone
modification is when molecules attach to the ‘tails’ of histone proteins, altering the activity of the
DNA wrapped around them and can change the structure of chromatin to euchromatin or
heterochromatin. Euchromatin is transcriptionally active and less compacted, whereas
heterochromatin is more compacted and less transcriptionally active.
The epigenome changes based on signals from inside the cell, neighbouring cells or from the
environment. The signals can come from direct contact (nervous system development), short
distance factors (blood clotting) or long distance factors (hormones) or the environment (all 3 the
aforementioned).
What are Prion Proteins?
Prions form when proteins called cellular prion protein are incorrectly folded, and result in disease
(for example Creutzfeldt-Jacob disease). They are found primarily on the cell surface of the central
nervous system, but are also found in other tissues in mammals.
Discuss memory and learning by categorising them. Discuss any possible problems with
investigating the underlying genotypes to these phenotypes
1. Short –term memory is information you’re only storing in memory temporarily, like a phone
number you heard on the radio.
2. Long term memory has two categories:
a. Declarative memory. Memory of facts and events, and includes semantic memory
and episodic memory. Semantic memory is ‘general knowledge’, memory of things
we have accumulated throughout our lives, like the names of colours. Episodic
memory is our memory of events/ personal experiences, including what happened,
when, where, who and why etc. Episodic memory is not static and is susceptible to
change when recalled (which is a problem with witness contamination, when
witnesses of an event discuss what happened it can alter how they remember the
event)
b. Procedural memory. The memory of skills (knowing how to do things) for example
riding a bike.
For long term memories to be formed proteins need to be synthesised which will ultimately change
the connections between neurons. Protein synthesis is controlled by gene expression. Gene
expression determines when and how much of a protein should be made.
There are two categories of genes that affect memory formation.
1. Genes that prevent short-term memory formation include latheo, linotte, 14-3-3 (Leonardo),
scabrous (volado) fasII and DCO.
2. Genes affecting long-term memory retention include dCREB2, AdfI (nalyot), Notch, crammer
and nebula
For long- term memories, the changes in the connections of the neurons are permanent or long
lasting. For short-term memory the changes in the synaptic connections are temporary. Both are
possible due to the brain's plasticity.
Complex traits are traits controlled by multiple genes and where there is interaction between the
genes and the environment. The genes controlling the trait act additively, contributing to the
phenotype. To look for the threshold effect, the frequency of the disorder among relatives of
affected individuals is compared with the frequency of the disorder in the general population. Risk of
developing the disorder should decrease with decrease in degree of relatedness (first degree
relatives have half their genes in common, second degree relatives a quarter, etc.)
A threshold exists above which the abnormal phenotype is expressed.
Explain how the number of loci contributing to a trait, also contributes to continuous variation.
Continuous variation is the distribution of phenotypic characteristics from one extreme to another in
an overlapping and continuous fashion, thus showing a lot of variation. If there are multiple loci
contributing, it would produce more phenotypic ‘classes'. Also, environmental variation will lead to
more phenotypic variation through GEI and GEC
How can the significance of QTL contributing to a phenotype be determined?
To determine which candidate gene(s) in an interval containing the QTL actually correspond to the
QTL include:
Identifying potentially functional DNA polymorphisms between alternative alleles of one of the
candidate genes
Observing a difference in mRNA expression levels between homozygous genotypes
Observing expression of RNA or protein in tissues thought to be relevant to the trait
Observing failure of a mutation in the candidate gene to complement the QTL
Observing that a mutant allele of the candidate gene affects the behaviour
For association studies: independent replication of the association
Explain behavioural plasticity by referring to the epigenetic landscape.
Epigenetics is the change in phenotype without changing the DNA sequence, by changing gene
expression through DNA methylation or histone modification. Your genotype determines the
boundaries of phenotypical variation, and epigenetics controls the variation within those
boundaries.
, DNA methylation is when methyl groups are added to certain bases to repress gene activity. Histone
modification is when molecules attach to the ‘tails’ of histone proteins, altering the activity of the
DNA wrapped around them and can change the structure of chromatin to euchromatin or
heterochromatin. Euchromatin is transcriptionally active and less compacted, whereas
heterochromatin is more compacted and less transcriptionally active.
The epigenome changes based on signals from inside the cell, neighbouring cells or from the
environment. The signals can come from direct contact (nervous system development), short
distance factors (blood clotting) or long distance factors (hormones) or the environment (all 3 the
aforementioned).
What are Prion Proteins?
Prions form when proteins called cellular prion protein are incorrectly folded, and result in disease
(for example Creutzfeldt-Jacob disease). They are found primarily on the cell surface of the central
nervous system, but are also found in other tissues in mammals.
Discuss memory and learning by categorising them. Discuss any possible problems with
investigating the underlying genotypes to these phenotypes
1. Short –term memory is information you’re only storing in memory temporarily, like a phone
number you heard on the radio.
2. Long term memory has two categories:
a. Declarative memory. Memory of facts and events, and includes semantic memory
and episodic memory. Semantic memory is ‘general knowledge’, memory of things
we have accumulated throughout our lives, like the names of colours. Episodic
memory is our memory of events/ personal experiences, including what happened,
when, where, who and why etc. Episodic memory is not static and is susceptible to
change when recalled (which is a problem with witness contamination, when
witnesses of an event discuss what happened it can alter how they remember the
event)
b. Procedural memory. The memory of skills (knowing how to do things) for example
riding a bike.
For long term memories to be formed proteins need to be synthesised which will ultimately change
the connections between neurons. Protein synthesis is controlled by gene expression. Gene
expression determines when and how much of a protein should be made.
There are two categories of genes that affect memory formation.
1. Genes that prevent short-term memory formation include latheo, linotte, 14-3-3 (Leonardo),
scabrous (volado) fasII and DCO.
2. Genes affecting long-term memory retention include dCREB2, AdfI (nalyot), Notch, crammer
and nebula
For long- term memories, the changes in the connections of the neurons are permanent or long
lasting. For short-term memory the changes in the synaptic connections are temporary. Both are
possible due to the brain's plasticity.
