selfish genes Flashcards
(21 cards)
what are Alarm calls in Belding’s ground squirrels like
- Give alarm calls when a predator approaches: an altruistic action
-Sherman & colleagues studied the evolution of alarm calls in groups
-The likelihood of an individual giving an alarm call was related to whether the group contains relatives or not.
-Tested empirically by putting individuals into different groups
-Consequently there is a potential cost to giving an alarm call. In a study to look at this behaviour, it was found that the probability that an individual would give a call was a function of the number of relatives nearby. Thus, if a large number of relatives were nearby, an individual was more likely to give a call than if there were few relatives nearby
what are Helpers at nest
-Florida Scrub Jay
- In most bird fledglings leave the nest when they are able to fly
-In some the chicks stay at the nest
-These sacrifice their own reproduction
-Help their parents to raise more broods so there are more brothers and sisters
is altruistic behaviour an evolutionary conundrum
-Altruistic behavior potentially challenges evolutionary ideas
-Selection favours the spread of genes if they code for traits that increase fitness
-A gene that codes for altruistic behaviour will surely help other genes?
when does selection occur
-Selection occurs when genotypes differ in their ability to pass genes on to the next generation
-If a genotype is successful, its genes will increase in frequency
-If a genotype is unsuccessful, its genes will decrease in frequency
-doesnt mention individuals
whats kin selection
-Explanation for altruistic behaviour
-Altruistic behavior increases the survival and reproduction of other individuals
-i.e. increases the fitness of others
-Those other individuals are kin (relatives)
-i.e. possess the same genes
-Altruistic genes increase the rate of spread of themselves via relatives
when is altruistic behaviour favoured
-if it benefits kin
- r x b > c
-r is relatedness of target individual
-b is benefit to target
-c is cost to giver
squirrels with kin behaviour
-Here is a squirrel – it is in a group of relatives that share one of its genes denoted by the stars. The others, without the stars, don’t share the genes
-Imagine we have a predator that is likely to eat some of the population
-These are the ones that are eaten, which include quite a few of the squirrel’s relatives
-hence those copies of the gene are lost from the population
-Imagine now that the population consists of non-relatives so that noone carries copies of the genes
-The predator arrives
-The sequirrel gives an alarm call that alerts the predator to it
-And it is nailed – it dies and so does the only copy of the gene in the population.
-Howver if the population contains lots of relatives then if the individual gives the alarm call, the others are saved
-And even though one copy of the gene is saved, all of the others survive
what is relatedness
-Offspring - parent = 0.5
-Sibling- sibling = 0.5
-Grandparent – grandchild = 0.25
-Cousin – cousin 0.125
-Relatedness is the proportion of genes shared because of common ancestry
Kin Selection is Gene Selection
- r x b > c
-r is probability that a member of kin contains a gene for an altruistic act
-b is number of extra copies of the gene the act yields
-c is cost to giver in terms of lost number of copies of the gene that individual produces
-look at slides 32-35
when will s gene spread in a population
- A gene will spread in a population if it causes more copies of itself to be produced
-Kin selection is the most obvious example
-But kin selection not strictly the only mechanism
——————> Selfish genes
why the term selfish
-Anything that a gene can do to favour its own spread at the expense of others will be favoured by selection
-Altruism is only favoured by evolution if it increases the rate of spread of a gene
-Hence the term selfish
-The individual doesn’t play any role in this
-It is just the outcome for the gene that is important
being selfish with the equation r b and c
r x b < c (individual perspective) and r x b > c (with siren) (gene perspective)
how does Selection acts on genes
-Genes are contained with individuals
-Individuals actually reproduce and die
-But selfish genetic considerations are more important
-Examples of when this is the case
what are Green Beard Genes
-Under kin selection it pays to be altruistic towards kin: you know the likelihood that they share genes
-An altruism gene that is linked to an obvious phenotype will spread if possessors are altruistic towards each other
-e.g. a green beard signifying that owner possesses a given gene
-Does not require relatedness
-genetic linkage of green beard gene and altruism gene
green beard examples
-Actually few examples… so kin selection probably more common!
-However a few have been described
-These are important because they demonstrate the principle of gene level selection
what are the Green-beard effects in red fire ants
-All egg laying queens are Bb
-bb queens die naturally
-BB queens are killed by Bb workers
-Use odours to distinguish BB from Bb
-Genotype linked to behaviour, hence a green beard effect
whats the green beard effect in Blue beards in lizards
-Unrelated male lizards form partnerships to protect territories
-These have blue throats
-Under some circumstances one of the males may have no offspring = ‘true altruism’
-Genes for throat colour and cooperation are linked
-Hence a true green-beard effect
green beard effects
-Relatively few examples
-‘false-beards’ can easily ‘cheat’
-Cheating: possess the green beard but do not reciprocate altruism
-Green beards are probably -evolutionarily unstable
-Kin selection probably more common
-But Green Beard effect is a logical consequence of gene-level selection
-These are important because they demonstrate the principle of gene level selection
what are the Selfish Genetic Elements
-Example that gene-selection is more important than individual selection
-Gene level selection affects evolution of genetic material
-Within genome competition
-e.g. Meiotic drive- evolved as direct competion with genes in same organism in meiosis
what happens with Segregation distorter in Drosophila
-So the effect is illustrated graphically here - as shown at the top, in classic Medelian systems, 50% of gametes are of each genotype in a heterzygous individual.
-On the other hand, in Drosophila a gene ‘sd’ when heterozygous with the wild type gene - denoted by ‘+’, leads to biased distributions of gamete genotypes in males. About 90% of the gametes are of the ‘sd’ genotype, because this gene directly inhibits the development of ‘+’ type gametes.
-This is an example of an adaptation that benefits the gene – the sd gene spreads at the expense of the wild type, although there is no benefit (and arguably a cost) to the individual.
whats a rule for evolution
-Selection acts on REPLICATORS
-These are individual units that replicate themselves
-Those that leave most copies are the most successful
