Topic 5- Evol Theory Flashcards
(81 cards)
The origins of life
- Earth is around 4.5 billion years old.
- The earliest fossil record of bacteria is dated to about 3.6 billion years ago.
- The first eukaryote (cell with nucleus) evolved between 2.7 & 1.5 billion years ago.
- The first multicellular organism appeared 640 million years ago.
Emergence of vertebrates
- The first vertebrates evolved some 525 million years ago.
- Reptiles first emerged 320 million years ago.
- Dinosaurs emerged around 230 million years ago.
- Mammals emerged about 200 million years ago.
- Primates emerged around 65 million years ago (PNAS, 2010 107 (11): 4797–4804)
Lineage
- A series of ancestral and descendant populations through time.
- Usually refers to a single evolving species, but may include several species descending from a common ancestor.
Gene
unit of heredity, DNA
Gene frequency
what percentage of the individuals in the population have this gene
Biological evolution:
occurs when there is a change in gene frequency in a population over time
Genome
- The entire complement of DNA sequences in a cell or organism.
- A distinction may be made between the nuclear genome and the organelle genomes (e.g., those of mitochondria and plastids).
Genotype
- The set of genes possessed by an individual organism.
* May refer to an organism’s genetic composition at a specific locus or set of loci under consideration.
Allele
- One of multiple forms of the same gene, presumably differing by a mutation of the DNA sequence.
- Alleles are usually recognized by their phenotypic effects.
Trait
A trait is a distinct variant of a phenotypic character of an organism that may be inherited, environmentally determined, or be a combination of the two.
• No trait is perfect.
• Every trait must be analyzed in terms of the benefits and costs of the trade-offs inherent in a particular trait.
• Natural selection favors traits that improve the fitness (reproductive success) of individuals and their kin.
Fitness
- The success of an entity in reproducing.
- The average contribution of an allele or genotype to the next generation or to succeeding generations.
- Genes that generate traits that increase an individual’s fitness are more likely to be passed to the next generation
Evolution steps
IMPORTANT
• Step 1: The origin of genetic variation
by random mutation or recombination followed by
• Step 2: changes in frequencies of alleles and/or genotypes, caused by natural selection and/or random genetic drift
Origins of variation
- Mutation
* Recombination
Mutations
• Random
• Result in change in DNA sequence
• May have no effect on fitness of organism
• May be harmful (reduce fitness) to
organism
• May be beneficial (increase fitness) to organism
• May be beneficial in one way and harmful in another way to the organism
Recombination
- Individuals inherit their genes and not their genotype from their parents.
- The meiotic cell division that forms the male and female gametes in sexually reproducing organisms involves two processes (recombination and assortment/segregation) which shuffle parental alleles into a unique combination in each egg or sperm.
- Every egg produced by a female and every sperm produced by a male are unique.
Two processes in meiosis which shuffle genes
• 1st is recombination during which homologous chromosomes exchange segments of DNA sequence, thereby creating new allele combinations on each chromosome.
• 2nd is independent assortment/segregation
of chromosomes into haploid gametes.
Variation
Individual members of a species vary in traits that effect their ability to compete for resources and reproduce.
Inheritance
Some subset of this variation is heritable.
Selection
Differential survival and reproduction among these variant forms leads to increased representation of successful traits in the next generation
Genetic Drift
Random changes in frequencies of alleles and/or genotypes within a population.
Evolution
Natural selection or/and random genetic drift over generations produces change in composition of frequencies of alleles and/or genotypes in a lineage
• Change in gene frequency may be due to selection that increases reproductive success
• Change in gene frequency may also be generated by random processes which dominate when the genetic of phenotypic variants do not differ in their effect on reproductive success, that is, when their variation is neutral compared to fitness
Allele frequency
- The proportion of gene copies in a population that are a given allele.
- The probability of finding a given allele when a gene is taken randomly from the population.
Genotype frequency
• The proportion of the population with a specific allele pair at a particular locus
Evolution
- Changes in frequencies of alleles and/or genotypes, caused by natural selection or/and random genetic drift.
- Such changes transpire by the origin and subsequent alteration of the frequencies of genotypes from generation to generation within populations, by alteration of the proportions of genetically differentiated populations within a species, or by changes in the numbers of species with different characteristics, thereby altering the frequency of one or more traits within a higher taxon.