Biology Ch 12. Genetics and Evolution Flashcards
Chromosomes
Contain genes in a linear sequence
Genes
Genetic sequences that code for heritable traits that can be passed from one generation to the next, organized in a linear sequence into chromosomes
Alleles
The alternative forms of a gene
Dominant allele
Requires only one copy to be expressed
Recessive allele
Requires two copies to be expressed
Genotype
The combination of alleles one has at a given genetic locus
Locus
Location on a specific chromosome for each gene, consistent among human beings
Homozygous
Having two of the same allele
Heterozygous
Having two different alleles
Hemizygous
Having only one allele, ex. the male sex chromosome
Phenotype
The observable manifestation of a genotype
Complete dominance
When the effect of one allele completely masks the effect of another
Codominance
When more than one dominant allele is present
Incomplete dominance
No dominant alleles, heterozygotes express a phenotype that is intermediate between the two homozygous genotypes
Penetrance
The proportion of a population carrying the allele who actually express the phenotype, or the probability that, given a particular genotype, a person will express the phenotype
Expressivity
The varying phenotypic manifestations of a given genotype
Mendels first law (of segregation)
States than an organism has two alleles for each gene, which segregate during meiosis, resulting in gametes carrying only one allele for a trait
Mendels laws
Help explain the inheritance of genes from parent to offspring
Mendels second law (of independent assortment)
States that the inheritance of one allele does not influence the probability of inheriting an allele for a different trait
The Griffith Experiment
Demonstrated the transforming principle, converting non-virulent live bacteria into virulent bacteria by exposure to heat-killed virulent bacteria
The Avery-MacLeod-McCarty experiment
Demonstrated that DNA is the genetic material because degradation of DNA led to a cessation of bacterial transformation
The Hershey-Chase experiment
Confirmed that DNA is the genetic material because only radio labeled DNA could be found in bacteriophage-infected bacteria
Full penetrance
Individuals with more than 40 sequence repeats, all individuals with their allele show symptoms of Huntington’s disease
Constant expressivity
All individuals with a given genotype express the same phenotype
Variable expressivity
Individuals with the same genotype may have different phenotypes
Recombination
Small segments of genetic material are swapped between chromatids in homologous chromosomes, resulting in novel combinations of alleles that were not present in the original chromosome, allows for the inheritance of one gene to be independent of the inheritance of all others, complicated by discovery of linked genes
Gene pool
All of the alleles that exist within a species
Mutations
Changes in the DNA sequence
Nucleotide mutations
Point mutations and frameshift mutations
Point mutations
The substituting of one nucleotide for another
Frameshift mutation
Moving the three-letter transcriptional reading frame
Silent mutation
No effect on the protein, typically because wobble in genetic code
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, leads to changes for all downstream amino acids
Chromosomal mutations
Include larger-scale mutations affecting whole segments of DNA
Deletion mutations
Occur when a large segment of DNA is lost
Duplication mutations
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 mutations
Occur when a segment of DNA is swapped with a segment of DNA from another chromosome
Genetic leakage
A flow of genes between species through hybrid offspring
Genetic drift
Occurs when a 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
Wild type allele
Alleles that are considered “normal” or “natural”
Mutagens
Substances that cause mutations
Transposons
Can insert and remove themselves from the genome, will disrupt gene if inserted into middle of a coding sequence
Inborn error of metabolism
Class of deleterious mutations that result in defects in genes required for metabolism
Things that result in decreased genetic diversity
Genetic drift, founder effect, inbreeding, may reduce fitness of population
Inbreeding depression
Loss of genetic variation that results in decreased fitness
Outbreeding/Outcrossing
The introduction of unrelated individuals into a breeding group
Punnett squares
Visually represent the crossing of gametes from parents to show relative genotypic and phenotypic frequencies
Parent generation
Represented by P in punnett square
Filial generations
Offspring generations, represented by F1, F2… in punnett square
Monohybrid cross
Accounts for one gene
Dihybrid cross
Accounts for two genes
Sex-linked traits
Traits on the X chromosome that are more common in men because they only have one copy of the X chromosome so one recessive allele means they have the trait
Recombination frequency
The likelihood that two alleles being separated during crossing over in meiosis, proportional to the distance between the genes on the chromosome
Genetic maps
Can be made using recombination frequency, scale in centimorgans, 1 centimorgan = 1 % chance of recombination
Hardy-Weinberg Principle
States that if a population meets certain criteria (aimed at a lack of evolution), then the allele frequencies will remain constant
Criteria: Population large No mutations that affect gene pool Mating is random No migration of individuals Genes are equally successful at being reproduced
Allele frequency
How often an allele appears in a population
Hardy-Weinberg Equilibrium
When allele frequencies remain constant in a population
Biometric techniques
Quantitative approaches to biological data
Test cross
Crossing an organism of an unknown genotype with a organism that is homozygous recessive to determine the unknown genotype
Hardy Weinberg equations
p - freq of dominant allele q - freq of recessive allele p^2 - freq of homozygous dom 2pq - freq of heterozygous q^2 - freq of homozygous recessive
p+q=1
p^2+2pq+q^2=1
Natural selection
States that chance variations exist between individuals and that advantageous variations afford the most opportunities for reproductive success and will thus pass those variations on to their offspring
Advantageous variations
Those that increase an individuals fitness for survival or adaption to the environment
Modern synthesis model
neo-Darwinism - accounts for mutation and recombination as mechanisms of variation and considers differential reproduction to be the mechanism for reproductive success
Differential reproduction
When a mutation or recombination that is favorable occurs, that chance will more likely pass on to the next generation and it will become more common
Inclusive fitness
Considers an organisms success to be based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others, survival of offspring or relatives ensues appearance of genes in subsequent generations, promotes the idea that altruism can improve the fitness and success of a species as a whole
Punctuated equilibrium
Considers evolution to be a very slow process with intermittent rapid bursts of evolutionary activity
Stabilizing selection
Keeps phenotypes in a narrow range, excluding extremes
Directional selection
Moves the average phenotype toward one extreme
Disruptive selection
Moves the population toward two different phenotypes at the extremes and can lead to speciation, reason for polymorphisms
Speciation
The formation of new species through evolution
Adaptive radiation
The rapid emergence of multiple species from a common ancestor, each of which occupies its own ecological niche
Species
The larges group of organisms capable of breeding to form fertile offspring, reproductively isolated from each other by pre or post zygotic mechanisms
Reproductively isolated
Once evolution has lead to enough changes that these populations could no longer freely interbreed
Prezygotic mechanisms
Prevent formation of the zygote completely, includes temporal isolation, ecological isolation, behavioral isolation, reproductive isolation, and gametic isolation
Postzygotic mechanisms
Prevents reproductive success after the zygote is formed, includes hybrid inviability, hybrid sterility, and hybrid breakdown
Divergent evolution
Occurs when two species sharing a common ancestor become more different
Parallel evolution
Occur when two species sharing a common ancestor evolve in similar ways due to analogous selection pressures
Convergent evolution
Occurs when two species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures
Molecular clock model
States the degree of difference in the genome between two species is related to the amount of time since the two species broke off from a common ancestor
Fitness
Level of reproductive success, directly related to the relative genetic contribution of this individual to the next generation
Polymorphisms
Naturally occurring differences in form between members of the same population, such as light and dark coloration in the name species of butterfly
Niche
A specific environment, including habitat, available resources, and predators for which a species is specifically adapted
