Lecture 5 Flashcards
Natural selection
What is natural selection
The process in which beneficial traits that are heritable become more common in successive generations
What is adaptations
Over time, natural selection results in adaptations
Changes in populations of living organisms that promote their survival and reproduction in a particular environment
What is reproductive success
The liklihood of an individual contributing fertile offspring to the next generation
What are the two categories of traits stemming from reproductive success
Certain characteristics make organisms better adapted and more likely to survive to reproductive age
Traits directly associated with reproduction, such as the ability to find a mate and ability to produce viable gametes and offspring
What is the modern description of natural selection
Within a population, allelic variation arises from random mutations that cause differences in DNA sequences
Some alleles encode proteins that enhance an individuals survival or reproductive capability compared to other members of the populations
Individuals with beneficial alleles are more likely to survive and contribute their alleles to the gene pool of the next generation
Over the course of many generations, allele frequencies of many different genes may change through natural selection, thereby significantly altering the characteristics of a population
What is fitness
Relative likelihood that a genotype will contribute to the gene pool of the next generation as compared to other genotypes
Measure of reproductive success
Possible genotypes are: AA, Aa, aa
What is the mean fitness of the population
The average reproductive success of members of a population
As individuals with higher fitness values become more prevalent, natural selection increases the mean fitness of the population
What is directional selection
Individuals at one extreme of a phenotype range have a greater reproductive success in a particular environment
Initiators:
- New allele with higher fitness introduced
- Prolonged environmental change
Stabilizing selection
Favors the survival of individuals with intermediate phenotypes
Extreme values of a trait are selected against
Clutch size:
- Too many eggs and offspring - die due to lack of care and food
- Too few eggs - does not contribute enough to next generation
Disruptie/Diversifying Selection
Favors the survival of two or more different genotypes that produce different phenotypes
Likely to occur in populations that occupy heterogeneous environments
Members of the populations can freely interbreed
Balancing selection
Maintains genetic diversity
Balanced polymorphism
Two or more alleles are kept in balance and maintained in a population over the course of many generations
What are the two common ways in balancing selection
- For a single gene, heterozygote favored
- Negative frequency-dependent selection
What is sexual selection
Form of natural selection
Directed at certain traits of sexually reproducing species that make it more likely for individuals to find or choose a mate and/or engage in successful mating
In many species, affects male characteristics more intensely than it does female
What is sexual dimorphism
Significant difference between the morphologies of the two sexes within a species
Intrasexual selection
Males directly compete for mating opportunities or territories
Between members of the same sex
Members of one sex, usually females, choose their mates from individuals of the other sex based on desirable characteristics
