genetics and variations
What is the difference between a genotype and a phenotype, and how does each contribute to an organism’s traits?
A genotype is the combination of alleles an organism has, influenced by genetic makeup and environment. A phenotype is the physical, physiological, or behavioral characteristics expressed by the genotype. Genotypes determine potential traits, while phenotypes are what actually appear.
How does natural selection affect the allele frequencies of polygenic traits, and what are the three types of selection involved?
Natural selection acts on the range of phenotypes in polygenic traits, shifting allele frequencies based on which traits increase fitness. The three types are:
Directional selection: favors one extreme phenotype.
Stabilizing selection: favors the average phenotype.
Disruptive selection: favors both extreme phenotypes over the average.
What is speciation, and how is reproductive isolation related to it?
Speciation is the formation of new species. It occurs when populations become reproductively isolated, meaning they can no longer interbreed and produce fertile offspring. This separation prevents gene flow and allows the populations to evolve independently.
What is binomial nomenclature, and who developed this system?
Binomial nomenclature is a system for giving organisms a two-part scientific name (genus + species). It was developed by Carl Linnaeus, a Swedish scientist.
What are the three domains of life, and how are they different in terms of cell structure and organization?
The three domains of life are Bacteria, Archaea, and Eukarya. Bacteria and Archaea are both made of prokaryotic cells, which means they lack a nucleus. However, bacteria have cell walls made of peptidoglycan, while archaea have unique cell membrane lipids and different cell wall compositions. Eukarya are composed of eukaryotic cells, which have a true nucleus and membrane-bound organelles, and include organisms such as plants, animals, fungi, and protists.
How does allele frequency relate to the concept of evolution in a population?
Allele frequency is the number of times a specific allele appears in a gene pool. Evolution occurs when the relative frequency of alleles in a gene pool changes over time.
What is genetic drift, and why is it more significant in small populations?
Genetic drift is the random change in allele frequencies due to chance events. It's more significant in small populations because chance events can more easily affect allele representation when there are fewer individuals.
Describe and give an example of behavioral isolation.
Behavioral isolation occurs when two populations develop different courtship behaviors or mating rituals, preventing interbreeding.
Example: Eastern and Western meadowlarks do not interbreed because they use different songs to attract mates.
What is a dichotomous key, and how is it used in classification?
A dichotomous key is a tool that uses a series of paired statements or questions to help identify and classify organisms based on their characteristics.
Explain the difference between monophyletic, paraphyletic, and polyphyletic groups in evolutionary classification.
In evolutionary classification, a monophyletic group includes a common ancestor and all of its descendants, representing a complete branch of the evolutionary tree. A paraphyletic group contains a common ancestor and some, but not all, of its descendants, leaving out certain lineages. A polyphyletic group is formed from species that do not share an immediate common ancestor, often grouped together based on similar traits that evolved independently.
Explain the role of mutations in generating genetic variation within a population.
Mutations are changes in DNA that can introduce new alleles into a gene pool, thereby increasing genetic variation and potentially affecting allele frequencies.
Describe the difference between the bottleneck effect and the founder effect as types of genetic drift.
Bottleneck effect: occurs when a large population is drastically reduced by an event (e.g., natural disaster), changing allele frequencies in the surviving population.
Founder effect: occurs when a small group from a population colonizes a new area, and the new population has different allele frequencies from the original.
How does geographic isolation contribute to the formation of new species?
Geographic isolation happens when physical barriers (like rivers, mountains, or bodies of water) separate populations. This isolation limits gene flow, and natural selection causes the separated groups to diverge over time into different species.
Example: Abert’s and Kaibab squirrels were separated by the Grand Canyon.
Define the term "taxa" and explain the goal of forming taxa in systematics.
Taxa (singular: taxon) are groups of organisms that are classified together. The goal of forming taxa in systematics is to organize and categorize organisms based on shared characteristics and evolutionary relationships.
What is a cladogram, and what type of information does it convey about organisms?
A cladogram is a diagram that shows the evolutionary relationships between different organisms based on shared derived characteristics. It illustrates which species are more closely related to each other by grouping them according to common ancestors. However, a cladogram does not indicate the exact amount of time that has passed or the degree of genetic change.
What are homologous chromosomes, and how can they carry different alleles for the same gene?
Homologous chromosomes are pairs of chromosomes (one from each parent) that are similar in shape and size and carry the same types of genes. However, they can carry different alleles (versions) of those genes.
What is genetic equilibrium, and under what five conditions is it maintained according to the Hardy-Weinberg Principle?
Genetic equilibrium is a state where allele frequencies in a population remain constant, meaning no evolution is occurring. The five Hardy-Weinberg conditions are:
Large population size
No mutations
No random mating
No gene flow (immigration/emigration)
No natural selection
What is the difference between premating and postmating isolation mechanisms?
Premating mechanisms prevent mating from occurring in the first place (e.g., behavioral, geographic, or temporal isolation).
Postmating mechanisms occur after mating, such as when gametes cannot fuse, or when offspring are inviable or infertile.
What is the difference between Linnaean classification and evolutionary (phylogenetic) classification?
Linnaean classification groups organisms based on physical similarities and hierarchical ranks (kingdom, phylum, etc.), while evolutionary (phylogenetic) classification groups organisms based on shared evolutionary ancestry and descent.
Why are shared genes considered more reliable than morphology when constructing evolutionary trees?
Shared genes are considered more reliable than morphology for constructing evolutionary trees because genetic information is less influenced by environmental factors and convergent evolution. While different species might look similar due to similar environmental pressures, their DNA sequences provide precise data about their evolutionary history, making genetic comparisons more accurate for determining relationships.
List and briefly describe three main sources of genetic variation
Mutations – introduce new alleles.
Sexual reproduction – shuffles alleles and creates new combinations.
Lateral gene transfer – genes transferred between organisms (common in bacteria), introducing variation.
Why doesn’t sexual reproduction alone cause changes in allele frequencies within a population?
Sexual reproduction only reshuffles existing alleles into new combinations during meiosis. It does not create new alleles or change the frequency of existing alleles by itself.
Melonie
What is a clade, and what makes a group of organisms a valid clade in phylogenetic classification?
A clade is a group of organisms that includes a single common ancestor and all of its descendants. A valid clade must be monophyletic, meaning it includes the ancestor and all its descendants.
List the six kingdoms of life and identify one distinguishing feature of each.
The six kingdoms of life are Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia. Archaebacteria live in extreme environments and have unique cell membranes. Eubacteria have cell walls containing peptidoglycan. Protists are mostly unicellular eukaryotes and very diverse. Fungi absorb nutrients and have cell walls made of chitin. Plants are autotrophic and use photosynthesis with cell walls made of cellulose. Animals are multicellular heterotrophs without cell walls and usually have specialized tissues like muscles and nerves.