Natural Selection Flashcards
Unpredictability of Evolutionary Patterns
Evolution does not follow a predetermined or predictable pattern because it is influenced by random mutations, environmental changes, and genetic drift. These factors create diverse, non-linear outcomes rather than following a specific trajectory
Gregor Mendel’s Contributions to Genetics
He discovered the basic principles of heredity through experiments with pea plants. He established the laws of segregation and independent assortment, demonstrating how traits are inherited through discrete units called genes
Definition and Function of Genes
A segment of DNA that codes for a specific protein or function. Genes act as instructions for building and maintaining an organism, influencing physical traits, and controlling various biological processes
Definition and Function of Proteins
Proteins are complex molecules composed of amino acids that perform a wide range of functions in living organisms. They can catalyze biochemical reactions, provide support, such as collagen in connective tissue, and carry molecules throughout the body. Their diverse roles are due to the vast variety of amino acid sequences and structures, allowing proteins to function in virtually every cellular process
Definition and Significance of Mutations
Changes in the DNA sequence of an organism. They can introduce new genetic variations, which are the raw material for evolution, enabling populations to adapt to changing environments through natural selection. Mutations can be neutral, beneficial, or harmful, and their significance depends on the context of the organism’s environment
Random and Non-Random Aspects of Mutations/Natural Selection
Mutations occur randomly and introduce new genetic variations, without regard to whether they are beneficial. Natural selection is a non-random process that favors beneficial mutations, increasing the frequency of advantageous traits in a population. Thus, while mutation is a random event, natural selection systematically shapes the direction of evolutionary change
Theodosius Dobzhansky’s Quote
“Nothing in biology makes sense except in the light of evolution,” emphasizing that evolutionary theory is the foundation for understanding biological processes
Impact of Population Bottlenecks on Genetic Variability
If all humans were destroyed by an epidemic except a single tribe in New Guinea, the global human gene pool would suffer a severe loss of genetic variability. This would lead to reduced diversity and increase the risk of genetic disorders in future generations
Species
A group of organisms that can interbreed and produce fertile offspring. When living in the same geographical range, reproductive barriers, such as behavior isolation or incompatible mating rituals, keep species separate
Importance of Genetic Variability
It is crucial for populations because it enhances their ability to adapt to environmental changes, resist diseases, and reduce the likelihood of extinction
Ring Species
A group of geographically connected populations that can interbreed with neighboring populations but have diverged enough that the populations at the ends of the range cannot interbreed. This phenomenon illustrates gradual evolutionary change
George Gaylord Simpson’s View of Directed Evolution
He argued that there is no evidence for directed evolution, meaning that evolutionary changes are not guided by a predetermined plan or purpose. Instead, they are shaped by natural selection acting on random mutations
Overproduction in B Cell Evolution
B cells are produced in large numbers, similar to the overproduction of offspring in natural populations. This ensures a diverse array of B cells exists, increasing the likelihood that some will be able to recognize and respond to a wide range of pathogens
Heritable Variation in Receptors in B Cells
Each B cell has unique receptors on its surface, which are genetically determined and passed through cell division. This diversity is akin to heritable variation in organisms, providing the immune system with the potential to recognize and bind to a broad array of pathogens
Selection of Effective B Cells
Only B cells with receptors that can bind effectively to an antigen are selected to proliferate. This selection process mirrors natural selection in larger populations, where only individuals with beneficial traits survive and reproduce
Clonal Selection in B Cells
When a B cell receptor weakly binds to an antigen, the immune system selects that B cell for clonal expansion. This process leads to the production of a large population of nearly identical B cells, enhancing the body’s ability to fight the pathogen
Genetic Rearrangement and Hypermutation of B Cells
During clonal expansion, antibody genes undergo genetic rearrangement and hypermutation, creating slight variations in the receptors. B cells with better binding receptors are selected, while poorly binding ones are eliminated, similar to how advantageous mutations are favored in evolution
Formation of Memory B Cells
After repeated rounds of selection and adaptation, a group of memory B cells is created. These cells have receptors that bind almost perfectly to the pathogen and are retained in the body for future encounters, enabling a faster and more effective response
Primary vs Secondary Immune Response
The primary immune response occurs when the body is first exposed to a new pathogen, leading to a slow and weak antibody production. The secondary immune response is faster and more robust due to the presence of memory B cells, which allow the immune system to recognize and respond to the pathogen more efficiently
Immunity Explained
Occurs when the body is equipped with memory B cells that can rapidly produce antibodies upon re-exposure to a pathogen, preventing illness. Vaccinations mimic this process by stimulating the primary response without causing disease
Role of Vaccines in Immune Response
Vaccines simulate the primary immune response, preparing the immune system to launch a strong secondary response if exposed to the actual pathogen. This reduces the risk of severe illness and promotes long-term immunity
Pathogen Evolution and Vaccine Updates
Pathogens like flu viruses evolve rapidly, altering their surface proteins and evading immune detection. As a result, vaccines must be updated regularly to match circulating strains, ensuring continued protection
Adaptation Through Natural Selection in Immune Responses
The immune system’s adaptation to pathogens mimics natural selection. B cells with more effective receptors are selected and proliferate, leading to a stronger and more specialized immune defense
Danger of Primary Response Without Vaccination
Without vaccination, the first exposure to a pathogen can be dangerous because the primary immune response is slow and weak. The delay in producing sufficient antibodies can lead to severe illness or death before the immune system fully adapts
