Models of Selection
One can speak of the fitness of an individual or a genotype or an allele. Fitness can also be measured on a relative scale: Relative Fitness = The average contribution to the offspring generation relative to the contribution of another type .
How do you calculate relative fitness?
The most direct way is to mate a heterozygous male fruit fly to a female of known homozygous genotype. You will then be able to determine the number of each genotype of offspring, which will give you the relative fitness of each allele.
What does a relative fitness of 1 mean?
The other thing to notice is that the mean relative fitness is always one (should be obvious), and that those genotypes that will increase in frequency have a relative fitness greater than one, and those that will decrease in frequency have a relative fitness less than one.
What is an example of relative fitness?
If dolphins typically have three babies in their lifetime, and a particular dolphin has four babies, she has a higher relative fitness. Relative fitness refers to the absolute fitness of the organism divided by the average number of offspring in a given population .
How do you calculate average fitness?
Though we are considering selection acting on genotypes, we can calculate the average fitness of each allele (called the Marginal fitness) by multiplying the probability that an allele finds itself in a particular genotype by the fitness of that genotype .
Why is relative fitness important?
which is only important because it shows that we can in fact talk about the rate at which selection works . The relative fitness highlights a couple of important points, however. Most importantly the relative fitnesses have the term (1-sq), that is there is a gene frequency in them.
Which is an example of inclusive fitness?
The most obvious examples of increased inclusive fitness can be observed in the altruistic behaviors of parents . To ensure that their genes remain in the gene pool, organisms attempt to give rise to the maximum number of offspring that are sure to survive.
What are fitness traits?
Fitness traits, also referred to as life-history traits, include measures of fertility and mortality and are complex phenotypes that are direct targets of Darwinian selection . ... Standing variation in any of those genes could contribute to interindividual differences in fitness in natural populations.
Is PP genotype or phenotype?
A simple example to illustrate genotype as distinct from phenotype is the flower colour in pea plants (see Gregor Mendel). There are three available genotypes, PP ( homozygous dominant ), Pp (heterozygous), and pp (homozygous recessive).
What is absolute fitness vs relative fitness?
There are several ways to measure fitness; for example, “absolute fitness” measures the ratio of a given genotype before and after selection while “relative fitness” measures differential reproductive success — that is, the proportion of the next generation’s gene pool that is descended from a particular organism (or ...
What causes genetic drift?
Genetic drift can be caused by a number of chance phenomena , such as differential number of offspring left by different members of a population so that certain genes increase or decrease in number over generations independent of selection, sudden immigration or emigration of individuals in a population changing gene ...
How do you explain natural selection?
Natural selection is the process through which populations of living organisms adapt and change . Individuals in a population are naturally variable, meaning that they are all different in some ways. This variation means that some individuals have traits better suited to the environment than others.
What is genotype fitness?
Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it. ... A genotype’s fitness includes its ability to survive, find a mate, produce offspring — and ultimately leave its genes in the next generation.
How do you determine the genotype fitness?
The selection coefficient (s) of a given genotype as related to the fitness or adaptive value (W) of that genotype is defined as s = 1 – W . (Fitness is the relative probability that a genotype will reproduce.)
Is a gene a pool?
A gene pool is the total genetic diversity found within a population or a species . A large gene pool has extensive genetic diversity and is better able to withstand the challenges posed by environmental stresses.
