Genetics and Evolution Flashcards
Alleles
alternative forms of a gene
Genotypes
combination of alleles one has at a given genetic locus
Homozygous
Heterozygous
Hemizygous –> having one allele ( male sex chromosome)
Phenotype
the observable manifestation of the genotype
Complete dominance
when the effect of one allele completely masks the effect of another
Codominance
has more than one dominant allele (AB blood)
Incomplete dominance
has no dominant allele; heterozygotes have an intermediate phenotype
Penetrance
the proportion of a population with a given genotype who express this phenotype.
the probability that, given a particular genotype, a person will express the phenotype.
Expressivity
the different manifestations of the same genotype across the population.
If expressivity is constant, then all individuals with a given genotype express the same phenotype
If expressivity is variable, then individuals with the same genotype may have different phenotypes.
Mendel’s first law of (segregation)
states that an organism has two alleles for each gene, which segregate during meiosis, resulting in gametes carrying only one allele for a trait.
can be seen through monohybrid cross
Mendel’s second law of (independent assortment)
states that the inheritance of one allele does not influence the probability of inheriting an allele for a different allele.
can be seen through dihybrid cross
Griffith experiment
demonstrated the transforming principle, converting non-virulent live bacteria into virulent bacteria by exposure to heat-killed virulent bacteria
Avery-MacLeod experiment
demonstrated the DNA is the genetic material because degradation of DNA led to a cessation of bacterial transformational
Hershey-Chase
confirmed that DNA is the genetic material because only radiolabeled DNA could be found in bacteriophage-infected bacteria
Point mutation
substituting of one nucleotide for another
Silent mutation
has no effect on the protein
Missense mutation
results in the substitution of one amino acid for another
Nonsense mutation
results in substitution of a stop codon for an amino acid
Frameshift mutation
moving three-letter transcriptional reading frame
Insertion or deletion
results in a shift in the reading frame, leading to changes for all downstream amino acids.
Deletion (chromosomal mutation)
occurs when a large segment of DNA is lost
Duplication (chromosomal mutation)
occurs when a segment of DNA is copied multiple times
Inversion (chromosomal mutation)
occurs when a segment of DNA is reversed
Insertion (chromosomal mutation)
occurs when a segment of DNA is moved from one chromosome to another
Translocation (chromosomal mutation)
occurs when a segment of DNA is swapped with a segment of DNA from another chromosome
Genetic leakage
the 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 –> small population of a species finds itself in reproductive isolation from other populations as a result of natural barriers.
Bottleneck –> suddenly reduce the size of the population available for breeding, b/c breeding group is small, inbreeding.
Crossing two heterozygotes with complete dominance
Aa x Aa = 1:2:1 genotypic ratio
3:1 phenotypic ratio
Test cross
used to determine an unknown genotype.
The organism with an unknown genotype is crossed with an organism known to be a homozygous recessive.
Heterozygous Dihybrid cross: PpTt x PpTt
Phenotypic ratio: 9:3:3:1 , (9 Tall and Purple) (3 Tall and white) (3 dwarf and Purple) (1 dwarf and white)
[12 tall : 4dwarf] [12purple : 4white]
Chiasma
further apart two genes are, the more likely it is that there will be a point of crossing over
Recombination frequency
the likelihood that two alleles are separated from each other during crossing over.
Hardy-Weinburg principle
states that if a population meet certain criteria, then the allele frequencies will remain constant.
p^2 + 2pq +q^2 = 1
p + q = 1
the equation to use to demonstrate that evolution is not occurring in a population.
Conditions to meet Hardy-Weinburg principle
- The population is very large (no genetic drift)
- No mutation that affects the gene pool
- Mating between the individual in the population is random
- No migration of individuals into or out of the population
- The gene in the population are all equally successful at being reproduced
Moderon synthesis model (neo-Darwinism)
accounts mutation and recombination as mechanisms of variation and consider differential reproduction to be a mechanism for reproductive success.
Inclusive fitness
the measure of an organism’s success in population, based on a number of offspring, success in supporting offspring, and ability of the offspring to then support others.
Punctured equilibrium
punctured equilibrium suggests that change in some species occurs in rapid bursts rather than evenly over time.
Stabilizing selection
keeps phenotype in a narrow range, excluding extremes
Directional selection
move the avg phenotype toward one extreme.
Favors one side more than other
Disruptive selection
moves the population toward two different phenotypes at the extremes and can lead to speciation.
Polymorphisms
naturally occurring differences in form between members of the same population. such as light and dark coloration in the same species of butterfly.
Adaptive radiation
the rapid rise of a number of different species from a common ancestor.
Prezygotic mechanisms
prevent the formation of zygote completely.
temporal isolation: breeding at different times
ecological isolation: living in different niches within the same territory
behavioral isolation: lack of attraction between members of two species.
reproductive isolation:
gametic isolation: intercourse occurs, but fertilization cannot occur
Postzygotic mechanisms
allow for gamete fusion but yield either nonviable or sterile offspring.
hybrid inviability: formation of the zygote that cannot develop to term.
hybrid sterility: formation of a zygote that cannot reproduce
hybrid breakdown: formation of first-generation hybrid offspring viable and fertile but the second generation are sterile and inviable.
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 way 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.
