BIOL - Lecture 2 Flashcards
Adaptation
Inherited characteristics of organisms that enhance survival and reproduction in specific environments
Darwin’s theory on how adaptations evolved
Variation
Heritability
Not all survive/reproduce
Best adapted (most “fit”) survive and reproduce
It lacks genetics
Giraffe case for adaptation
Observation: Giraffe necks vary in length which is heritable (genes). Not all giraffes can survive and reproduce.
Hypothesis: Giraffes with longer necks are able to eat leaves that are unavailable to their competitors
Inference: Giraffes with longer necks survive better and reproduce more. Genes for longer necks accumulate in the population.
Giraffes didn’t develop long necks to get the high leaves, the ones with longer necks just had more offspring.
Microevolution
Individuals do not evolve, populations do.
Change in allele frequencies that occurs over time in a population.
Populations
A group of individuals in the same species that live in the same area and interbreed.
Trees of the same species evolve differently on different islands and become 2 separate populations.
Basic unit of evolution.
Individuals grow and change in their lifetime, populations evolve.
Biological evolution can be defined as
Descent with modification (species change over time, give rise to new species, and share a common ancestor)
Change in the genetic composition of a population
Natural Selection acts on individuals but populations evolve
The modern synthesis
Darwin observed phenotypic variations but those represent differences in genetic composition.
Variations within a population
Individuals within a population can differ in many traits.
Not all variations are heritable. Some variations are purely environment based.
Traits that are acquired during an organism’s life (ie lost a limb) are not heritable.
Genotype and Phenotype influence
Phenotype does not always reveal genotype!
Changes in genotype affect phenotype but changes in phenotype do not affect genotype.
Diploid
A pair of homologous chromosomes
Haploid
Gamete
Different gamete possibilities equation
2^n
Sources of genetic variation
New alleles in a population coming from mutations (low/slow rate) or from gene flow.
New combinations through sexual recombination. It deals a unique “hand” to each individual.
Always remember that the heterozygous genotype has “double” the number. ie: Bb and bB
Variation
Must exist in a population for evolution to occur, but it isn’t enough on its own. We need some other mechanism.
Darwin’s theory - Evolution by NS
- Species were not created in their present form, but evolved from ancestral species
*descent with modification - A mechanism for evolution: natural selection
Does NS act on phenotype or genotype?
Phenotype (what it can see/observe)
3 modes of NS
Directional selection - conditions favour individuals exhibiting one extreme of a phenotypic range, thereby shifting a population’s frequency curve for the pheno- typic character in one direction or the other
Disruptive selection - conditions favour individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
Stabilizing/balancing selection - acts against both extreme phenotypes and favours intermediate variants.
Evolution by natural selection is a blend of:
Chance and “sort- ing”: chance in the creation of new genetic variations (as in mutation) and sorting as natural selection favours some alleles over others. Because of this favouring process, the outcome
of natural selection is not random. Instead, natural selection consistently increases the frequencies of alleles that provide reproductive advantage, thus leading to adaptive evolution.
relative fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
Sexual selection
A form of NS that acts through access to mates.
Sexual dimorphism - male cardinals are red etc…
