Lecture 2 & 3 Flashcards
- Discuss an examination of the study of natural selection in the wild: evolution of beak size in medium ground finches - Explain how evolution is the change in allele frequencies in a population over time - Explain how mutations generate genetic variation - Define genetic drift and describe how it alters allele frequencies in populations - Using examples, explain how bottlenecks and founder effects are mechanisms of genetic drift - Describe how gene flow is a mechanism of evolution
Describe the research conducted by Peter and Rosemary Grant.
Determined that natural selection is variable over time and can result in rapid evolutionary change by tracking the beak sizes of the medium ground finch over the course of generations. A severe drought resulted in only harder, woody seeds being available to birds; finches with bigger beaks had a better change of surviving the drought, so the next generation inherited larger beaks on average. Heavy rain came to the island a few years later and produced a significant number of small seeds, so smaller beaks became favored.
What is a gene?
a segment of DNA whose nucleotide sequence regulates the expression of other genes
What are alleles?
two or more DNA sequences occurring at a particular gene locus
What is a genotype, and what are the three types of genotypes?
the genetic makeup of an individual organism
homozygous dominant (PP), homozygous recessive (pp), heterozygous (Pp)
What is a phenotype?
observable, measurable characteristics that occur as a result of a genotype
What is complete dominance?
the dominant allele completely masks the phenotypical effects of the recessive alleles; typically giving rise to just two different phenotypes
What is incomplete dominance?
incomplete dominance - both alleles of a gene at a locus are partially expressed, typically resulting in a variety of intermediate phenotypes
What is a population?
a group of individuals from the same species restricted to one area
What is the relationship between genetic variation and environmental change?
the more genetic variation within a population, the better equipped it is to respond to environmental change
What is adaptive evolution, and what is the mechanism that causes it?
the frequency of an advantageous trait in a population increases over time, and the favorable trait is continuously changing depending on shifting environmental pressures; caused by natural selection
What is evolution?
a change in allele frequencies in a population across generations
What is a mutation?
a change in the nucleotide sequence of an organism’s DNA; can create new alleles; considered the ultimate source of all genetic variation
What is gene expression?
the information in genes used by cells to produce proteins; mistakes in gene expression can give rise to mutations
What are the two types of mutations?
somatic mutations - affects cells in the body (soma) of an organism; not heritable in animals, but can be passed down during vegetative reproduction in plants
germline mutations - affects gametes (eggs, sperm) of an individual; heritable genetic variation that is relevant to evolution
What is one way that gene expression is regulated?
complementary base pairs: only particular base pairs can form hydrogen bonds between them to make DNA double stranded and able to form helix structure
guanine + cytosine; thymine + adenine
What is genetic drift?
a change in the gene pool of a population due to chance, not due to the selection of a favorable trait (i.e. a moose trampling flowers); results from random sampling error, which is higher with a smaller sample; reduces genetic variation in a population and alters allele frequencies
What is a fixed allele? What is a lost allele? What is the gene allele frequency for each? How does this relate to loci?
alleles that become a permanent part of the population, as opposed to lost alleles; gene allele frequency of a fixed allele is 100%; gene allele frequency of a lost allele is 0%; fixed and lost genes cannot be from the same locus - they are different alleles from multiple loci
What is a bottleneck? Provide an example.
an event that drastically reduces the size of a population and results in a non-representative set of alleles for subsequent populations, even after the population size rebounds (i.e. elephant seals)
What factors determine the probability of an allele making it through a bottleneck?
- the frequency of the allele before the bottleneck (rare alleles are more likely to be lost)
- the severity of the bottleneck (the severity of the population size drop during the bottleneck)
What is the founder effect? Provide an example.
a type of bottleneck resulting from a small number of individuals colonizing a new, isolated habitat (i.e. silvereye birds)
What is gene flow? Provide an example.
the transfer of alleles from one population to another, as a result of movement of individuals or gametes (i.e. common house mosquito, or pollen)
How does gene flow effect populations?
introduces variation into a new population; causes populations of the same species to become more homogenous to each other, but overall diversity still increases
What is recombination? How does it effect populations?
pieces of DNA are broken and recombined to produce new populations of alleles; generates variation and genetic diversity (along with mutations)
What is independent assortment? How does it effect populations?
states that the allele a gamete receives for one gene does not influence the allele received for another gene; ensures novel combinations of alleles
