Genetics and Evolution Flashcards
What are genes?
DNA sequences that code for heritable traits that can be passed from one generation to the next
What is a locus?
the location of the gene on a specific chromosome
What is a dominant allele?
only one copy of an allele needed to express a given phenotype
What is a recessive allele?
if two copies of an allele are needed to express a given phenotype
What is complete dominance?
when only one dominant and one recessive allele exist for a given gene
What is codominance?
when more than one dominant allele exists for a given gene
What is incomplete dominance?
occurs when a heterozygote expresses a phenotype that is intermediate
What is pentrance?
a population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype
What is expressivity?
defined as varying phenotypes despite identical genotypes; constant would mean that all individuals with a given genotype express the same phenotype
What is Mendel’s First Law of Segregation?
Genes exist in alternative forms (alleles) and each organism gets two alleles from each parent. The two alleles segregate during meiosis and that if the alleles are different, one will be silenced.
What is Mendel’s Second Law of Independent Assortment?
states that the inheritance of one gene does not affect the inheritance of another gene because of recombination
What is a gene pool?
all of the alleles that exist within a species
What are wild-type alleles?
alleles are considered “normal” or “natural” and are ubiquitous in the study population
What are mutagens?
substances that cause mutations
What is a mutation?
a change in DNA sequence
What is a transposon?
elements that can insert and remove themselves from the genome
What are point mutations?
occur when one nucleotide in DNA (A,C,T,G) is swapped for another; silent, missense, nonsense
What is a silent mutation?
occur when the change in nucleotide has no effect on the final protein synthesized from the gene; most common from the wobble position
What is a missense mutation?
occur when the change in nucleotide results in substituting one amino acid for another in the final protein
What is nonsense mutation?
occur when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein
What is a frameshift mutation?
occur when nucleotides are inserted into or deleted from the genome
-insertion or deletion mutations
What are chromosomal mutations?
larger-scale mutations in which large segments of DNA are affected
What is a deletion mutation?
occur when a large segment of DNA is lost from a chromosome; small deletion are considered frameshift mutations as described previously
What is a duplication mutation?
occur when a segment of DNA is copied multiple times in the genome
What is an inversion mutation?
occur when a segment of DNA is reversed within a chromosome
What is an insertion mutation?
occur when a segment of DNA is moved from one chromosome to another; small insertion mutations are frameshifts
What is translocation mutation?
occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome
What are advantageous mutations?
conferring a positive selective advantage that may allow the organism to produce filter offspring
What are inborn errors of metabolism?
an important class of mutations that caused defects in genes required for metabolism
What is genetic leakage?
flow of genes between species when two similar species mate and produce a hybrid
What is genetic drift?
to changes in the composition of the gene pool due to chance; more pronounced in small populations
What is the founder effect?
is a more extreme case of genetic drift in which a small population of a species finds itself in reproductive isolation from other populations as a result of natural barriers, catastrophic effects, or other bottlenecks
What are bottlenecks?
events that drastically and suddenly reduce the size of the population available for breeding
What is inbreeding?
mating between two genetically related individuals - encourages homozygosity
What are three ways that reduce genetic diversity?
genetic drift, founder effect, and inbreeding
What is inbreeding depression?
the loss of genetic variation may cause reduced fitness of the population
What is outbreeding/outcrossing?
the introduction of unrelated individuals into a breeding group; could increase fitness of the population
What is the biometric techniques?
quantitative approaches to biological data
What is monohybrid?
when only one trait is being studied in a cross (Punnett square)
What are the offspring of a cross called?
F generation or filial
What is a test cross?
used to determine an unknown genotype; an organism with an unknown genotype is crossed with an organism known to homozygous recessive aka “back crosses”
What is a dihybrid cross?
when two traits are being studied in a cross (Punnett square)
What is recombination frequency?
what the likelihood that two alleles are separated from each other during crossing other and is roughly proportional to the distance between the genes on the chromosome
What is a genetic map?
a map of the relative distance/positions of genes on a chromosome based on recombination frequencies
What is allele frequency?
how often an allele appears in a population
What are the criteria for Hardy-Weinberg equilibirum?
(1) The population is very large (no genetic drift)
(2) There are no mutations that affect the gene pool
(3) Mating between individuals in the population is random (no sexual selection)
(4) There is no migration of individuals into or out of the population
(5) The genes in the population are all equally successful at being reproduced
What is the Hardy-Weinberg equation?
p + q = 1 (frequency of alleles in the population)
p^2 + 2pq + q^2 = 1 (frequency of genotypes and phenotypes in the population)
What is natural selection?
the theory that certain characteristics or traits possessed by individuals within a species may help those individuals have greater reproductive success and pass those traits on
What is fitness?
level of reproductive success
What is the modern synthesis model?
updated version of Darwins; when mutation or recombination results in a change that is favorable to organism’s reproductive success
What is differential reproduction?
over time, traits that are favorable are passed down and become ubiquitous in the gene pool
What is inclusive fitness?
a measure of an organism’s success in the population, based on the number of offspring, success in supporting offspring and ability of the offspring to support others
What is punctuated equilibrium?
little evolution would occur within a lineage of related lifeforms for long periods of time, followed by an explosion of evolutionary change; supported by research
What is stabilizing selection?
keeps phenotypes within a specific range by selecting against extremes
What is directional selection?
pushes phenotypes to one end of the extreme spectrum
What is disruptive selection?
two extreme phenotypes are selected over the norm
What are polymorphisms?
naturally occurring differences in form between members of the same population
What is adaptive radiation?
rapid rise in the number of different species from a common ancestor
What is a niche?
a specific environment for which a species is specifically adapted to
What is a species?
the largest group of organisms capable of breeding to form fertile offspring
What is speciation?
the formation of new species through evolution
What is isolation?
the progeny of two populations are no longer able to interbreed (so new species) due to changes over time
What are prezygotic mechanisms?
prevent formation of zygote completely; breeding at different times, ecological isolation, behavioral isolation, differences in reproductive anatomy or fertilization can’t occur
What are postzygotic mechanisms?
allow for gamete fusion but yield either nonviable or sterile offspring; formation of a hybrid that cannot be brought to term, sterile offspring, hybrid breakdown (sec gen can’t breed)
What is divergent evolution?
when lineages that share a common ancestor start to development different characteristics
What is parallel evolution?
related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures
What is convergent evolution?
when two lineages that do not share a common ancestor start to develop the same characteristics due to similar adaptive pressures
What is the molecular clock model?
correlating the degree of genetic similarity with the amount of time since two species split off from the same common ancestor
