Task 3 GENES AND NATURAL SELECTION IN POPULATIONS Flashcards
Purifying selection
occurs when an allele that does something useful is fixed at a locus. Whenever a mutation occurs at this locus it will decrease the fitness and gets weeded out
o Variation reducing
Stabilizing selection
describes selection where current population average contains the optimum fitness. Individuals higher or lower in this trait have reduced fitness
o When a population lives in the same environment for a time there will be stabilizing selection
Directional selection
Occurs when optimum of fitness is not the average of the population. Phenotypes that differ in the right direction are according to this higher in fitness
o Produces mutations in the favourable genotype in the long run. And accounts for change
Disruptive selection
When there is no medium and both high and low extremes are favoured
Heterozygotes advantage
describes the situations where individuals with one copy have a higher fitness than individuals with no or two copies of an allele
o ß-globin gene: When Homozygote it can lead to strokes because of changes in blood cells, When heterozygotes these risks are smaller but it still has the beneficial effect of being more resistant to malaria
Negative frequency-dependent selection
the situation where the phenotype is high in fitness when it is rare but not when it is common. The result is that it will stabilize at an intermediate frequency
Force of mutation
genetic variation will persist if the force of mutation is strengthened or that of selection weakened
o For polygenic characteristics, the effective strength of mutation is proportional to the number of genes involved, b.c. each gene has the possibility of mutation
Inconsistent selection
variation might persist when selection is inconsistent
o Occurs when the selective optimum changes in an environment (Darwins finches)
Sexually antagonistic selection
The selection optimum might not be the same for males and females. E.g. height (because costs more energy to be tall)
o So when a male with high fitness gets a female child it might be low in fitness
o Leads to more variety
Adaptionist hypothesis
if some features or behaviour is commonly found in a species it means that it is probably an efficient design which was the solution for a problem which the species faced
Ultimate explanation
the explanation how the that particular design increased in ancestral fitness
Proximate explanation
the account of the genetic features that led to the formation of that characteristic
Human sickle disease
The case of the malaria protecting gene, changes the blood structure so that it is less effective in transporting oxygen or fighting disease
Exponential growth
the exponential growth of a population without selection
Reproductive success
Determined by the number of viable descendants produced
Fitness
determined by the number of copies of an allele in the next generation. When there are two alleles the fitness is determined by the proportion of both
Time lags
There is a time lag between the optimal phenotype and the actual population because it will always take several generations to reach the optimal state
Selective regime
Environment changes and so the optimal phenotype does
o Phenotypic plasticity: the ability of the phenotype to respond to changes within one generation
Genetic correlations
the situation between two traits in which selecting for the one traits effects the other as well (pleiotropy and linkage)
Hitch-hiking traits in fox domestication
They took foxes and after 30-35 generations they were responsive to humans. Other characteristics changed as well despite they were only aiming for tameness
Trade-offs in groupies
arises when two traits have opposite effects on fitness but are genetically correlated with each other.
Shape of adaptive landscape
Some changes that might lead to progression in the long run have to reduce fitness first, so they won’t have the chance to express it
Optimally modelling
The investigator uses a hypothesis derived from reverse engineering and guesses with the use mathematical forms under natural selection what design features would we expect to have?
Nomological networks
A network based on different sciences to find a proof for evolution/selection
Should be combined and not subject focused
Sexual dimorphism
The difference between male and female forms of the same species
Sexual selection
is natural selection on the ability to gain mates
Batemans principle
male reproductive success increases with each additional partner mated to a greater extent than is true for females
Lek
The showoff from males to impress on females to be able to have sex with them
Intrasexual competition
An example would be fighting of males
the sexy son hypothesis
if there is any initial slight preference amongst females for a males with longer trails, then the preference for the long tail and the length of tze tail itself co-evolve to both become even greater over time.
The good genes hypothesis
Special looks are costly so they are supposed to have enough spare energy to evolve them.
Extra-pair matings
matings that take place with a male other than the social partner
o Females using extra-pair matings to get better genes for their offspring
Sex ratio
The sex ratio is always 50/50 and selection would bring it back if it changes
• Birds with nest helpers in high quality territories were higher in reproductive success, but when the territories were low in quality any helper decreased the reproductive success (this accounts for no 50/50 distribution)
• Local resource competition, and local resource enhancement, are two examples in which deviations from a 50:50 sex ratio have been successfully predicted
Founder effect
few individuals become isolated from larger population and establish a new gene pool different from source population
Bottleneck effect
few individuals become isolated from larger population and establish a new gene pool different from source population
Neutral variation
differences in DNA sequence that don’t give an organism a selective advantage/ disadvantage
Mutation selection balance
mutation introduces genetic variation into population while selection reduces it
–>level of genetic diversity depends on the relative strength of the two
