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| The combined effects of genetic alleles at two or more gene loci are equal to the sum of their individual effects. |
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| The proportion of variation that is inherited genetically. If the heritability is 0 then all variation is due to the environment whilst if all heritability is 1 all the phenotypic variation is purely genetic. |
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| Accounts for the evolution of exagerrated male ornamentation by persistant female choice. |
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| Gustaggsson 1986, have the attractive male trait of a white patch on their forehead. The larger the patch the more desirable they are. |
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| Life time reproductive success |
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| Is the number of offspring that are laid and successfully make it to the adult stage. |
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| This is where Greater sage Grouse males go to an area to find a mate. Leks are arenas with especially high sexual selection. Females should always cause strong directional selection for sexually selected characters. What you would expect under Fisher's paradox is that all the traits females are choosing from are heritable but they shouldn't really be bothered as there are no genetics to choose from under Fisher's paradox. |
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| Two problems with Fisher's paradox |
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Definition
Why is the heritability of fitness characters lower for some characters than for others?
Why isn't heritability for fitness zero, as it should be under strong selection? What maintains genetic variation in fitness. |
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| What maintains genetic variation for fitness? |
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Definition
Mutation-selection balance
Fluctuating selection
The existence of genetically-based tradeoffs
Non-additive genetic variation
Sexually antagonistic selection |
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| Mutation-selection balance |
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Definition
| Selection removes variation whilst mutation puts it back in and these process come to an equilibrium. The rates are not enough to explain the observed amount of variation in natural populations. |
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Fluctuating selection is a mode of natural selection characterized by the fluctuation of the direction of selection on a given phenotype over a relatively brief period of evolutionary time. |
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| Example of fluctuating selection |
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| A species of plant may come in two varieties: one which prefers wetter soil and one which prefers dryer soil. |
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| Example of fluctuating selection |
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Definition
| Copepods custaceans - there is a seasonal way they lay their eggs. In the winter their eggs develop immediately and in the spring eggs with a summer diapause sink onto sediment and are resistant to digestion so that they can avoid intense fish predation in the summer. They can detect photoperiod which is a highly heritable trait. If the copepods switch too early they lose out in competition but if the switch too late they get eaten by years. |
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| The existence of genetically-based tradeoffs |
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Definition
| There is a boundary beyond which those genotypes cannot go. There is little variation in fitness remains, but lots in the components of fitness. If the environment changes, gene expressions are altered due to genes and environment interactions. |
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| Example of a genetically-based tradeoff |
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Definition
| Soay sheep of St Kilda (Johnston et al., 2013). Males have different types of horn, some males have small curves and some don't have horns at all. This is based on one gene. If you are heterozygous then you get small horns but if you are homozygous wildtype then you get full horns. Most individuals are wild-type. If you are homozygous mutants then you suffer in male reproductive success. This genotype is still in the population as they survive better. This advantage is what maintains this allele ien the population. |
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| Non-additive genetic variation |
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Definition
| Sometimes, one allele, the dominant one, masks expression by its partner, the recessive allele. The organism will display the dominant trait if it has either one or two copies of the dominant allele for that trait. The recessive trait prevails only if the organism is homozygous for the recessive allele (that is, if it has two copies of the recessive gene.) This is a nonadditive genetic pattern. |
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| An example of non-additive genetic variation |
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Definition
| n example occurs in the texture of peas, which can be smooth or wrinkled, denoted “S” and “s.” The allele for smooth peas is dominant, meaning that SS or Ss will express the smooth trait, but only ss will result in the wrinkled variety. |
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| This is the suppression of the effect of one such gene by another. |
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| Red quirrel population fluctuate in reposonse to previous year's cone density. The amount of resources given to pup by the mother changes on how she sees the environment and therefore effects their growth rate. When there is more food available the growth rate was higher. When the same noises where played back and there wasn't actually more food the growth was still higher due to how the mother perceived the environment. Mothers estimate the conditions of the future and so make their offspring prepared for the future using these estimations. (Dantzer et al., 2013) |
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| Sexually antagonistic selection |
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Definition
| Direction of selection may be different between sexes. |
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| Sexually antagonistic selection example |
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Definition
| Red Deer (Foerster et al., 2007) there is a tradeoff between optimal genotypes of males and females. For example highly fit fathers have less fit daughter and fitter sons which could maintain genetic variation. |
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| We want to analyse relationships among species and use this to explain adaptations however species are not independent units; they are connected by their evolutionary past. |
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| How do we solve the problem of phylogeny? |
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| We have to determine evolutionary relationships by creating a phylogenetic tree and tehn allow for his in comparative analyses. |
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