evo. lecture 2 Flashcards
Microevolution
genetic basis of inheritance and biological evolution, population genetics, natural selection, and adaptation.
Macroevolution
speciation, how evolution works on a grand scale, and modern synthesis.
Genetics, Chromosomes, and DNA Molecules
- nucleus: part of a eukaryotic cell containing genetic material.
- somatic cells: all the cells of your body that aren’t gametes.
- gametes: a sex cell; sperm or an egg.
- chromosomes: double-stranded DNA molecule in nucleus of eukaryotic cells that carries genes and functions in the transmission of hereditary information.
- DNA (deoxyribonucleic acid): a hereditary material in (most) organisms used to store genetic info that codes for the synthesis of proteins.
- variation is maintained, achieved, and altered by DNA.
RNA Molecules
- RNA: single-stranded nucleic acid.
- the primary function of RNA in a cell is the step between DNA and protein synthesis.
- does all the work making the proteins.
Proteins
- protein: a large molecule composed of a specific sequence of amino acids.
- proteins are what allows us to live, breathe, and survive. (they do so by producing enzymes.)
- amino acid: one of a class of 20 molecules that are combined to form proteins in living things.
Transcription
- synthesis of single strand of ribonucleic acid (mRNA) at unwound section of DNA with one of the DNA strands serving as a template.
- result: genetic information encoded in DNA transferred to RNA. mRNA carries information to cytoplasm.
Translation
- tRNA is information adapter molecule.
- direct interface between amino-acid sequence of protein and information in mRNA.
- decodes information in mRNA.
- acceptor stem where specific amino acid is attached.
- anticodon reads information in mRNA sequence by base pairing.
Codon
genetic information encoded in a sequence of three nucleotides.
Gene
basic, functional units of heredity.
Alleles (Dominant and Recessive)
- allele: one of several forms of the same gene.
- dominant: fully expressed in the phenotype.
- recessive: only expressed in the phenotype when it’s paired with an identical allele.
Genotype and Phenotype
- genotype: genetic makeup of an organism.
- phenotype: observable traits or characteristics of an organism.
Heterozygous and Homozygous
- heterozygous: different rather than identical alleles.
- homozygous: identical alleles in the corresponding loci of a pair of chromosomes.
Mutation
- mutation: an error or alteration of a nucleotide sequence, which represents the ultimate source of new genetic material in populations.
- most mutations do absolutely nothing (are not expressed).
- when they are expressed phenotypically, it’s usually so harmful that the organism dies off as a fetus.
- beneficial mutations are more likely to pop up in individuals in populations characterized by low overall fitness levels.
- different codons produce the same amino acids (redundancy) so that if a mutation occurs you won’t be affected.
- viruses can cause mutations and actually turn genes on and off.
Population Genetics
the study of distribution of allele frequencies and changes under the influence of the four main mechanisms of evolution: mutation, genetic drift, gene flow, and natural selection.
Natural Selection
- any consistent difference in fitness among phenotypically different biological entities.
- deterministic (not random) process involving differential reproductive success.
- acts only on existing variation.
- you can have natural selection without biological evolution, and vice versa.
Directional Selection
- evolutionary process that tends to favour either higher or lower values of a character than its current average value.
- promotes phenotypic variation, and has been suggested to be a primary cause of speciation.
Stabilizing Selection
- when an average phenotype within a population is fittest.
- reduces variations in form, which keeps phenotype aspects of individuals in a population constant through time.
Disruptive Selection
- when individuals at both extremes of a range of phenotypes are favoured against those intermediate.
- the evolutionary significance of disruptive selection lies in the possibility that the gene pool may become split into two distinct gene pools.
- when sustained, can lead to genetic variance.
Adaption and Acclimatization
- adaptation: a process in which any change in the structure or function of an organism allows it to survive and reproduce more effectively in its environment
- a characteristic that performs a function that is of utility to the organism possessing it.
- acclimatization: the short-term process of an organism adjust to chronic change in its environment (i.e. within one organism’s lifetime).
- these two are not the same thing!
Modern Evolutionary Synthesis
emphasizes combined action of random mutation, natural selection, genetic drift, and gene flow.
Cladistics
- system of biological taxonomy based on quantitative analysis of comparative data.
- used to reconstruct the (assumed) phylogenetic relationships and evolutionary history of groups of organisms.
- three major assumptions:
- changes in characteristics within lineages over time.
- all organisms are descended from a common ancestor.
- when lineage splits, divides into exactly two groups.
Cladogram
- a branching diagram used to illustrate phylogenetic relationships.
What Really Happened in Mendel’s F1 x F1?
- scientists replicated Mendel’s experiment and could never get the same numbers (3:1) ratio.
- this means that Mendel must have fudged his numbers!
Gene Flow | Population Genetics
- the movement of individuals, and therefore genes, between populations (of the same species).
- it takes very little gene flow to maintain reproductive potential in humans.
Genetic Drift | Population Genetics
- more likely to occur in small, isolated populations.
- changes gene frequencies.
- increases between-population variation.
- founder effects occur when a new subpopulation is composed of only a few individuals from the original population.
- population bottlenecks occur when there is a drastic reduction in a population’s size for at least one generation.
Node | Cladogram
the start point (internal) or end point (external) of a line segment in a cladogram.
Clade | Cladogram
a group that contains an ancestral taxon and all of its descendants.
Taxa | Cladistics
groupings of organisms given a formal scientific name such as species, genus, family, etc. (singular is taxon.)
Tree Topology | Cladogram
The branching patterns of lines connecting nodes and organisms.
How To Read a Cladogram
- choose taxa whose evolutionary relationships interest you.
- determine characters and examine each taxa.
- determine polarity of characters using an outgroup.
- group taxa by synapomorphies, not symplesiomorphies.
Character | Cladistics
features/visible traits/characteristics (e.g. cranial capacity or brow ridges).
Synapomorphy | Cladistics
derived characteristic.
Symplesiomorphy | Cladistics
ancestral characteristic.
Outgroup | Cladistics
reference point; species you’re looking at and comparing the others to.
Ingroup | Cladistics
all other groups that you’re comparing to the outgroup.
Misconceptions About Cladograms
- evolution produces patterns of relationships among organisms that are like a tree and not like a ladder.
- you should not assume that the taxon on the right are more advanced than the taxa on the left.
- avoid reading across the terminal nodes, the order of which has no meaning.
