Chapter 12- Genetics and Evolution Flashcards
homologues
each human possesses two copies of each chromosome (except the male sex chromosome)
hemizygous
genotypical situation in which only one allele is present for a given gene (as is the case for parts of the X chromosome in males)
incomplete dominance
heterozygote expresses a phenotype that is intermediate between the two homozygous geneotypes.
codominance
more than one dominant allele exists for a given gene
penetrance
population measure. proportion of individuals in the population carrying the allele who actually express the phenotype
expressivity
different manifestations of the same genotype across the population
two mechanisms that allow for greater genetic diversity in offspring
segregation and independent assortment (also crossing over)
transforming principle
nonvirulent bacteria acquired the ability to form smooth capsules from the dead virulent bacteria (Griffiths experiment)
transposons
small piece of DNA that can insert/remove itself from DNA
silent mutation
change in nucleotide has no effect on final protein synthesized from the gene
degeneracy
wobble in genetic code in the third nucleotide of a codon
missense mutation
change in nucleotide results in substituting one amino acid for another in the final protein
nonsense mutations
occur when change in nucleotide results in substituting a stop codon for an amino acid in the final protein
chromosomal mutations
larger-scale mutations in which larger segments of DNA are affected
translocation mutations
occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome
deleterious
detrimental (one class is “inborn errors of metabolism)
inborn errors of metabolism
class of deleterious mutations. defects in genes required for metabolism.
genetic leakage
flow of genes between species
genetic drift
changes in composition of the gene pool due to chance. more common in smaller populations
founder effect
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 a natural barrier/bottlenecks
bottlenecks
drastically and suddenly reduce size of population available for breeding
what can decrease genetic diversity?
genetic drift, the founder effect, inbreeding
inbreeding depression
loss of genetic variation may cause reduced fitness of the population
outbreeding/ outcrossing
introduction of unrelated individuals into a breeding group
what do P and F stand for?
P generation- parent
F generation- filial (offspring)
test cross/ back crosses
when determining an unknown genotype you cross the unknown organism with one that is known to be homozygous recessive
unless told otherwise, what is always assumed about X-linked (sex-linked) traits?
that they are recessive (ex: hemophilia)
recombination frequency
the likelihood that two alleles are separated from each other during crossing over (roughly proportional to the distance between the genes on the chromosome)
in a genetic map what is a map unit and what does it correspond to?
map unit = centimorgan, which corresponds to 1% chance of recombination occurring between two genes.
5 criteria met for Hardy-Weinberg equilibrium
MEANS THAT NO EVOLUTION IS OCCURRING
- large population (no genetic drift)
- no mutations that affect gene pool
- mating b/w individuals in the population is random (no sexual selection)
- no migration of individuals in or out of population
- genes in population are all equally successful at reproducing
Hardy-Weinberg equations
p + q = 1
p^2 + 2pq + q^2 = 1
differential reproduction
when mutation/ recombination results in a favorable change then its more likely to pass on to the next generation (opposite is also true)
inclusive fitness
measure of an organisms success in the population (based on number of offspring and ability of offspring to support others)— helping others of the same species- promotes idea that altruistic behavior can improve the fitness and success of a species as a whole.
punctuated equilibrium
changes in some species occur in rapid bursts rather than evenly over time.
stabilizing selection
selecting against extremes (regular bell-curve) - ex: human birth weight
directional selection
adaptive pressure can lead to the emergence/ dominance of one extreme phenotype
disruptive selection
two extreme phenotypes are selected over the norm
adaptive radiation
rapid rise of a number of different species from a common ancestor. allows various species to occupy different niches, which decreases competition for limited resources
speciation
formation of a new species through evolution
pre and post-zygotic mechanisms resulting from reproductive isolation
pre- prevent formation of zygote
post- allow for gamete fusion but yield either nonviable or sterile offspring
divergent evolution
two species with common ancestor become less similar b/c of different evolutionary pressures
parallel evolution
two species with a common ancestor remain similar because of similar evolutionary pressures
convergent evolution
two species with no recent common ancestor become more similar b/c of similar evolutionary pressures
molecular clock model
degree of difference in the genome b/w two species is related to the amount of time since the two species broke off from a common ancestor
