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Chapter 4

LIFESCI 2D03 Chapter Notes - Chapter 4: Arginine, Single-Nucleotide Polymorphism, Genetic Linkage


Department
Life Sciences
Course Code
LIFESCI 2D03
Professor
Rashid Khan
Chapter
4

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Animal Behaviour Chapter 4
Behavioural Genetics
Genetic predisposition: genes influence behaviours
Dog breeders use natural variation in behaviour to select dogs with appropriate traits to breed
(artificial selection)
Genes are not the sole determination of whether a behavioural trait will be present in an individual;
the environment plays a large role as well
4.1 Behavioural variation is associated with genetic variation
Phenotype: observable traits
An individual’s behaviour is the result of three factors:
1. Genotype (G): genetic makeup, all the alleles of an individual
2. Environment (E): the conditions an individual has experienced and their effect on its
behavioural phenotype
3. Gene-environment interactions (GEI): interactions between a genotype and an
environment that influence the behavioural phenotype
The Search for a Genetic Basis of Behaviour
- Instinct: behaviours that are performed the same way each time, are fully expressed the
first time they are exhibited, and are present even in individuals raised in isolation
Because all individuals in a species exhibit innate, non-learned behaviours, these
behaviours must have a genetic basis and are heritable.
- Reflex: one kind of innate behaviour; an involuntary movement in response to a stimulus
- Fixed action pattern: behaviours that are invariant and unlearned. Once initiated, they are
brought to completion.
- Greylag geese (Tinbergen and Lorenz)
Lay their eggs in nests on the ground, roll displaced eggs back into the nest using
their beaks
Newly hatched birds assume a characteristic crouching pattern when they observe
a predator silhouette
Behavioural Differences between Wild-type and Mutant Fruit Flies (Bastock, 1956)
- Wild type: the typical form of an organism or gene that occurs in nature
- Bastock (1956) noticed that there were relatively low number of yellow fruit flies
(Drosophila melanogaster) in comparison to black, and wondered whether the gene
mutation in mutant yellow flies might induce a behavioural change that resulted in very low
reproductive success in the wild.
- Fruit fly courtship process: male follows female, taps her with his pheromone-containing
foreleg, begins a wing vibration, licks the female, and then copulation begins if she accepts
it
- Bastock interbred black and yellow flies for several generations to create flies that had very
similar genomes except for the gene that codes for yellow versus black. She then
conducted mating trials with both types of males and wild-type females.
- Wild-type males had an overall higher mating success, mated sooner, exhibited more
courtship behaviours (wing vibration and licking)
- Bastock used the phenotype to study the genotype.
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Major and Minor Genes
- Major gene: individual gene that is responsible for a large fraction of phenotypic variation
- Minor gene: Individual gene that contributes to small amounts of variation in the phenotype
Molecular Techniques
- Microarray Analysis (Gene Expression Profiling)
Measures the amount of mRNA produced as an indicator of gene activation
Allows us to examine hundreds of genes at once by quantifying which genes are
activated in different individuals or tissues
A cDNA library is made using DNA from different tissues or individuals, cDNA are
made to fluoresce and then introduced into a DNA chip containing the genome
sequence of the original animal, where it will bind to its complimentary piece and
be easily localized. The intensity of colour acts as an indication of gene expression
QTL Mapping to Identify Genes associated with Behaviour
- Quantitative trait loci (QTL): stretches of DNA that either contain or are linked to genes
influencing a trait such as behaviour
- QTL mapping: a statistical technique that combines genetic information with trait
information to determine which regions of the genome contain the genes that influence the
trait QTLs
- Candidate genes: major genes suspected of contributing to a large amount of phenotypic
variation in a specific trait
- Quantitative Trait Loci Mapping:
QTL: portions of the genome that influence certain phenotypic traits
A QTL analysis correlates regions of the genome that have genetic markers with
associated behavioural variation among individuals in a family
A family with behavioural variation is created through mating of individuals with
extreme traits, and then the behaviours of newer generational members are
assessed quantitatively
Information about each individual’s genotype is examined by cutting the DNA into
fragments and attaching genetic markers to identify each fragment. Genetic
markers are scattered throughout the entire genome.
Genetic marker: short sequence of known DNA; can be restriction fragment length
polymorphisms (fragments differ in length), simple sequence repeats (repeating
sequences of only a few known base pairs), or single nucleotide polymorphisms
(sequences that differ in only a single base pair nucleotide)
Statistical analyses are used to determine if differences in behaviour between
individuals correlate with differences in marker genotypes.
- QTL mapping for aphid feeding behaviour
Caillaud and Via (2012) used QTL analysis to examine the number of genes
involved with plant choice in pea aphids (alfalfa versus clover)
Aphids explore the plant prior to choosing by probing deeply to find phloem sap.
The duration of exploration behaviours varies greatly depending on whether the
aphid is on a preferred or non-preferred plant.
Individuals of the two extreme populations were crossed to create and F1 and an
F2 generation and the plant choice behaviour of the new generations was
observed
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Measured: time spent searching for a feeding site (exploration), time spent on a
plant before penetrating it with feeding tube, the latency to inject saliva into the
plant to begin digesting it, and the amount of time digesting sap from each plant
(rapid time to feed = strong preference)
The genotype of each individual was assessed using 116 amplified fragment
length polymorphism markers to create a linkage map
No QTL for latency to inject saliva in the plant was found, meaning that the
behaviour is probably influenced by multiple minor genes. QTLs were found for
each of the other three behaviours however, and the proportion of the behavioural
variation in these plant acceptance behaviours were explained with each QTL
ranging from 7% to over 50%.
- Linkage map: a genetic map of the relative positions of genetic markers on chromosomes
Fire Ant Genotype and Social Organization (Ross, 1997)
- Fire ants are social insects that live in large colonies, each of which has one or more
queens and many sterile workers and soldiers. Some colonies have one reproductive
queen (monogyne) and other colonies have multiple queens (polygyne).
- Question: What is the proximate explanation for whether a colony is monogyne or
polygyne? Do genes affect this variation in social behaviour?
- Methods: collected ants from both types of social colonies from both domestic Argentina
and introduced USA and used starch gel electrophoresis to analyze the genotypes of the
ants
- Results: The genotype and allelic frequencies at the Gp-9 locus differed between the two
colonies monogyne had Gp-9BB genotype and polygyne had Gp-9Bb genotype.
- Conclusion: the alleles at one locus in fire ants, Gp-9, appear to regulate the social
organization of a colony.
- Reason: Gp-9 gene codes for a pheromone-binding protein, which act as a chemical
recognition that allows ants to determine whether individuals are members of their colony
or a potential intruder. Individual workers only accept queens that produce the appropriate
chemical signal.
Experimental manipulation of gene function: Knockout Studies
- Knockout technique: a procedure in which a single gene is rendered non-functional
- Creating Knockout Organisms
Examine the behaviour of animals with and without an active copy of the gene in
effort to determine the function of the gene
Transgenic: animals that have had additional DNA added to their genome to stop
the particular gene (the knockout gene) from functioning
Typically, another marker gene is inserted for easy identification of knockout mice
(e.g. a gene that will produce a coat colour change)
Chimera: individuals that develop from two kinds of stem cells (mutant knockout
mice are chimeras because they develop from one kind of stem cell that contained
the mutation and another that did not)
- The researcher must know the location of a gene and its DNA sequence in order to alter
the gene so it cannot function.
- The behaviour of knockout individuals is compared with that of wild-type.
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