Exam #2 Flashcards
when does crossover happen
prophase 1 of meiosis
what results from crossover?
recombinants AND nonrecombinants
recombinants
result of crossover, the physical exchange of parts of homologous chromosomes
genetic map
diagram showing the relative position of genes along a chromosome
map unit
the distance between genes resulting in 1% recombination
when distances are less than 15 map units…
the map distances between adjacent genes can be added to get the distance between the genes at the ends
when distances are more than 15 map units apart…
the observed recombination frequency is somewhat smaller than the sum of the map distances between genes
epistasis
MULTIPLE genes affect phenotype; pliotropy = 1 gene MULTIPLE phentotypes
Harmful mutations are often eliminated in one or a few generations because
they decrease the survival and the capacity to reproduce of those affected
genotype-by-environment interaction
combination of homozygous (genes) and smoking (environment)
For X & Y sex chromosomes, reciprocal crosses…
are not equivalent
sex chromosomes
X and Y chromosomes
autosomes
chromosomes that are NOT sex chromosomes
X is ____(size)___ than Y
X is LONGER than Y
Regions of homology on tips of chromosomes…
allow pairing during meiosis (crossover)
Segregation of the sex chromosomes predicts…
a 1:1 ratio of females to males
who discovered x linked genes
Morgan; genetics of fruit flies
“wild type”
most common phenotype
Criss cross inheritance:
An X chromosome present in a male in one generation must be transmitted to a female in the next generation, and in the generation after that can be transmitted back to a male
Linked
genes that are close together in the same chromosome & do NOT assort INDEPENDENTLY
nonrecombinants
alleles are present in the same combination as the parent
crossover
the physical exchange of parts of homologous chromosomes, prophase 1 of meiosis
the frequency of recombination is a measure of…
the genetic distance between linked genes
if 2 genes are so close together that crossing over never takes place…
we would expect only nonrecombinant chromosomes
if 2 genes are located very far apart from each other..
1 or more crossovers will occur, and there will be a 1:1:1:1 ratio of nonrecombinant and recombinant gametes
maximum frequency of recombination
50%
natural selection results in…
allele frequencies changing from generation to generation according to the allele’s impact on the survival and reproduction of indiviuals
What did Malthus point out in his Essay on the Principle of Population?
natural populations have the potential to increase in size geometrically, meaning that populations get larger at an ever-increasing rate (does not actually happen doe)
fitness
a measure of the extent to which the individual’s genotype is represented in the next generation (reproduction)
paraphyletic
a group that includes a common ancestor and SOME but not all of its descendents
polyphyletic
group of organisms that does not include a common ancestor
taxa
tips of the branches that are groups of organisms
sister groups
two groups that are closest relatives bc they share a common ancestor not shared by any other group
speciation
the set of processes by which physically, physiologically, or ecologically isolate populations diverge from one another to the point where they can no longer produce fertile offspring
taxonomy
to recognize and name groups of individuals as species, and to group close species into more inclusive taxonomic group
phylogenetics
aims to discover the pattern of evolutionary relatedness among groups of species by comparing their anatomical or molecular features
phylogenetic tree
hypothesis about the evolutionary history of species
genus (plural: genera)
closely related species grouped together
taxonomic classification order
genus > family > order > class > kingdom >domain
characters
the anatomical, physiological, or molecular features that make up organisms
character states
several observed conditions
character states in diff. species can be similar for 1 of two reasons:
the character state was present in the common ancestor of the two groups and retained over time (common ancestry), OR the character state independently evolved in the two groups as an adaptation to similar environments (convergent evolution)
analogous
similarities due to independent adaptation by diff species (result of convergent evolution)
what is used in constructing phylogenetic trees?
only homologies
synamorphies
shared derived character
cladistics
phylogenetic reconstruction on the basis of synamorphies
parsimony
choosing the simpler of two or more hypotheses to account for a given set of observations
the extent of similarity (or distance) indicates…
how recently 2 groups shared a common ancestor
single gene traits
each one is determined by variation at a single gene and the traits for the most part are not influenced by environment
complex traits
(such as human height) influenced by multiple genes as well as by the environment…found in all organisms…important in human health and disease…phenotype determined by measurement
environmental risk factor
a characteristic in a person’s surroundings that increases the likelihood of developing a particular disease
inbred lines
true-breeding strains (homozygous)…often used for research
complex traits are affected by (one/many) genes
many
phenotypes of many complex traits show ___ distribution
normal
complex traits
both genetic factors and environmental factors contribute to variation in phenotype among individuals
norm of reaction
for any genotype graphically depicts how the environment (x axis) affects phenotype (y axis) across a range of environments
heritability
the proportion of the total variation due to genetic differences among individuals
when heritability is 100%…
slope of the line is 1; average phenotype of the offspring from any pair of parents will = the average phenotype of the parents themselves
when heritability is 0%…
the line representing the trait has a slope of 0. the average phenotype of offspring will be = to the average of the population as a whole, despite the phenotypes of parents
cultural transmission
some environmental effects in phenotype (ex: rich parents = rich kids)
Single nucleotide polymorphism (SNP)
site in the genome where either of two different nucleotide pairs can occur and where each nucleotide pair is common enough in the population to be present in a random sample of 50 diploid individuals …AKA single base changes in individuals
positive selection
natural selection that increases the frequency of a favorable allele
negative selection
natural selection that decreases the frequency of a deleterious allele
stabilizing selection
maintains status quo and acts against extremes (ex: human birth weight must be between both extremes) …keeps a trait the same over time (extremes are eaten)
directional selection
leads to a change in a trait over time (finches and their bills size for food) (skewed right or left)
artificial selection
form of directional selection…analogous to natural selection but the competitive element is removed
disruptive selection
operates in favor of extremes and against intermediate forms (apple maggot flies) (middle is eaten)
sexual selection
promotes traits that increase an individual’s access to reproductive opportunities
intrasexual selection
male vs male to get the girl
intersexual
not fighting, just compete for attention with bright colors and displays. IN THIS CASE, FEMALES CHOOSE
migration, mutation, genetic drift, and non random mating..
cause allele frequencies to change, but do NOT lead to adaptations
migration
movement of individuals from one population to another…results in gene flow (decrease pop’s average fitness…ex: white ppl going to the equator and getting sunburn and skin cancer)
gene flow
the movement of alleles from one pop. to another
mutation (increases/decreases) genetic variaton
increases; source of new alleles and the raw material on which other forces act…RARE
genetic drift
random change in allele frequencies from generation to generation
bottleneck
originally large pop. falls to just a few individuals (loss of genetic variation)
founder event
when a few individuals start a new population (small number of peeps arrive on an island and colonize it) (genetic variation is lost)
genetic drift has a large effect in…
small populations
why does nonrandom mating alter genotype frequencies without affecting allele frequencies???
it just rearranges alleles already in the gene pool and, unlike migration or mutation, does not add new alelles to the population
most evolutionarily significant form of non-random mating
inbreeding (increases the freq. of homozygotes and decreases the # of heterozygotes in a pop. without affecting allele frequencies)
The modern synthesis
combines mendelian genetics and darwinian evolution…several genes contribute to a trait
population genetics
the study of patterns of genetic variation
species
individuals that can exchange genetic material through interbreeding…a group of individuals capable of sharing alleles with one another
gene pool
different combos of alleles drawn from the species (human gene pool..skin color, hair type, eye color, etc)
populations
interbreeding groups of organisms of the same species living in the same geographical area
2 sources of genetic variation
mutation and recombination
somatic
body’s tissues
germ line
occurring in reproductive cells and then passed on to the next generation
allele frequency of an allele x is…
number of x’s present in the pop. divided by total number of alleles
fixed
population that exhibits only one allele at a particular gene
3 ways to measure genotype and allele frequencies in populations:
observable traits, gel electrophoresis, and DNA sequencing
@ genetic levels, evolution is simply…
a change in the frequency of an allele or a genotype from one generation to the next
5 hardy weinburg equilibrium conditions
- no natural selection 2. no migration 3. no mutation 4. large sample (no genetic drift) 5. non-random mating
allele frequencies…
p + q = 1 (are p and q)
genotype frequencies
p^2 + 2pq +q^2 (use for hardy weinburg) (each part)
species
groups of interbreeding populations that are reproductively isolated from other such groups
morphospecies concept
members of the same species usually look alike (shape, size, coloration)
probz with BSC
easier in concept than practice, does not apply to asexual (bacteria) or extinct organisms, ring species and hybridization complicate it
ring species
species with populations that are reproductively but not genetically isolated (because of gene flow)
hybridization
interbreeding (capable of exchanging genes with other species in their genera) …occurs mainly in plants
prezygotic isolating factors:
behavioral, gametic, mechanical, temporal, geographic/ecological
behavioral isolation
individuals mate only with other individuals based on courtship rituals, songs, or other behaviors (chimpanzees dont like humans)
gametic isolation
incompatibilities between the gametes of 2 diff species (plants)
mechanical incompatibility
genetalia (insects and animals)
temporal isolation
time; diff. times of year…or active only during day/night
geographic or ecological isolation
space. subtle. (bugs on specific plants)
postzgotic isolation factors:
genetic incompatibility
genetic incompatibility
genetic dissimilarity (diff # of chromosomes)
the more closely related/genetically similar a pair of species…
the less extreme the genetic incompatibility between their genomes
partially reproductively isolated
2 pops that have genetically diverged but not far enough for full reproductive isolation (speciation)
allopatric speciation
speciation that results from GEOGRAPHICAL separation of populations
subspecies
allopatric populations that haven’t evolved into speciation but have acquired population-specific traits
how does allopatric speciation occur
dispersal and vicariance
dispersal
some individuals colonize a distant place (like an island) far from the main source population
vicariance
geographic barrier arises within a single population, separating it into two or more isolated populations
peripatric speciation
specific kind of allopatric speciation where a few peeps from mainland disperse to a new location REMOTE from the original peeps and evolve separately (dispersal)
adaptive radiation
unusually rapid evolutionary diversification in which natural selection accelerates the rates of both speciation and adaption
co-speciation
occurs in response to speciation in another species (parasites)
sympatric populations
not genetically separated…DISRUPTIVE SELECTION
instantaneous speciation
caused by hybridization between 2 species in which the offspring are reproductively isolated from both parents (sympatric)
double diploid is called a…
tetraploid
polyploidy
multiple chromosome sets
allopolyploids
polyploids that are produced from hybridization of two diff species
autopolyploids
polyploids derived from an unusual reproductive event
reinforcement of reproductive isolation (reinforcement)
process by which diverging populations undergo natural selection in favor of traits that enhance prezygotic isolation, thereby preventing the production of less fit hybrid offspring (mating discrimination)
A mutation can go to fixation by selection if…
it is advantageous and by genetic drift
primates
mammals that share a # of features: nails rather than claws, front facing eyes, and opposable thumbs
humans closest relative is___
the chimpanzees
human and chimpanzee dna differ by just ___%
1% (King and Wilson)
hominins
species that have arisen on the human side of the human/chimpanzee split (ARDI)
bipedal
moving w/ 2 feet and walking upright – LUCY
first homonin
homo ergaster
neanderthals
EUROPE AND MIDDLE EAST
multiregional hypothesis
modern humans derive from h. ergaster that spread around the world 2 mya
out-of-africa hypothesis
modern humans arose from h. ergaster in africa before going to africa around 60K y.a
Cann’s ___
mtDNA
Cro-Magnon
first known pop. of homo sapiens in europe
explain why mtdna and the whole genome study may differ
- diff. patterns of transmission between mtDNA and genomic material (mtDNA from mama only) OR 2. ancient DNA stems from a sex-based difference in interbreeding (neanderthals were male)
neoteny
long term evolutionary process in which the timing of development is altered so that a sexually mature organism still retains the physical chracteristics of juvenile form
