Ch. 12: Genetics and Evolution Flashcards
Chromosomes
Contain genes in a linear sequence
Alleles
Alternative forms of a gene
- Dominant allele: requires only one copy to be expressed
- Recessive allele: requires two copies to be expressed
Genotype
Combination of alleles one has at a given genetic locus
Homozygous
Having two of the same allele
Heterozygous
Have two diff alleles
Hemizygous
Having only one allele (such as male sex chromosomes)
Phenotype
observable manifestation of a genotype
Complete dominance
Has one dominant allele and one recessive allele
Codominance
Has more than one dominant allele
Incomplete dominance
Has no dominant alleles; heterozygotes have intermediate phenotypes
Penetrance
The proportion of a population with a given genotype who express the phenotype
Expressivity
Varying phenotypic manifestations of a given genotype
Mendel’s laws:
Help explain inheritance of genes from parent to offspring
Mendel’s first law
Law of segregation: states that an organism has 2 alleles for each gene, which segregate during meiosis, resulting in gametes carrying only one allele for a trait
Mendel’s second law
Law of independent assortment: states that the inheritance of one allele does not influence the probability of inheriting a given allele for a diff trait
DNA as genetic material experiments
Griffith experiment: demonstrated that transforming principle, converting non-virulent bacteria into virulent bacteria by exposure to heat-killed virulent bacteria
Avery-MacLeod-McCarty: experiment demonstrated that DNA is the genetic material because degradation of DNA led to a cessation of bacterial transformation
Hershey-Chase: experiment confirmed that DNA is the genetic material bc only radiolabeled DNA could be found in bacteriophage- infected bacteria
Gene pool
All of the alleles in a given population
Mutations:
changes in DNA sequence
Point mutations
Substituting of one nucleotide for another
Frameshift mutations
Moving the three-letter transcriptional reading frame
Silent mutation
has no effect on the protein
Missense mutation
Results in the substitution of one amino acid for another
Nonsense mutation
Results in the substitution of a stop codon for an amino acid
Insertions and Deletions
Result in a shift in the reading frame, leading to changes for all downstream amino acids
Deletion mutation
Occur when a large segment of DNA is lost
Duplication mutation
Occur when a segment of DNA is copied multiple times
Inversion mutations
Occur when a segment of DNA is reversed
Insertion mutations
Occur when a segment of DNA is moved from one chromosome to another
Translocation mutation
Occur when a segment of DNA is swapped w a segment of DNA from another chromosome
Genetic leakage
Flow of genes between species through hybrid offspring
Genetic drift
Occurs when the composition of the gene pool changes as a result of chance
Founder effect
Results from bottlenecks that suddenly isolate a small population, leading to inbreeding and increased prevalence of certain homozygous genotypes
Punnett Squares
Visually represent the crossing of gametes from parents to show relative genotypic and phenotypic frequencies
Parent generation
Represented by P
Filial generations
Offspring, represented by F1, F2, and so on in sequence
Monohybrid Cross
Accounts for one gene
Dihybrid Cross
Accounts for two genes
Sex-linked crosses
Sex chromosomes are usually used to indicate sex as well as genotype
Recombination Frequency
Theta, is the likelihood of two alleles being separated during crossing over in meiosis
Genetic maps
Can be made using recombination frequency as the scale in centimorgans
Hardy-Weinberg Principle
States that if a population meets certain criteria (aimed at lack of evolution), the then the allele frequencies will remain constant (Hardy-Weinberg equilibrium)
Natural Selection
States that chance variations exist between individuals and that advantageous variations- those that increase an individual’s fitness for the environment- afford the most opportunity for reproductive success
Modern synthesis model (neo-Darwinism)
Accounts for mutation and recombination as mechanisms of variation and considers differential reproduction to be the mechanism of reproductive success
Inclusive Fitness
Considers an organism’s success to be based on the number of offspring, and the ability of the offspring to then support others; survival of offspring or relatives ensures continuation of genes in subsequent generations
punctuated equilibrium
Considers evolution to be a very slow process with intermittent rapid bursts of evolutionary activity
Different types of selection:
Lead to changes in phenotypes
Stabilizing selection
keeps phenotypes in a narrow range, excluding extreme
Directional Selection
Moves the average phenotype toward one extreme
Disruptive selection
Moves toward 2 diff phenotypes at the extremes and can lead to speciation
Adaptive radiation
Is the rapid emergence of multiple species from a common ancestor, each of which occupies its own ecological niche
Species
The largest group of organisms capable of breeding to form fertile offspring
Reproductively isolated
Species are reproductively isolated from each other by pre- or postzygotic mechanisms
Two species can evolve w different relationship patterns
- Divergent evolution: occurs when two species sharing a common ancestor become more different
- Parallel evolution: occurs when two species sharing a common ancestor evolve in a similar ways due to analogous selection pressure
- Convergent evolution: occurs when two species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures
Molecular clock model
The degree of diff in the genome between two species is related to the amount of time since the two species broke off from a common ancestor
