Chapter 23: the Evolutions of Populations Flashcards
What is MICROEVOLUTION and what was the example of it in class?
change in allele frecuencias in a population over generations
ex. ground finch,
The medium ground finch (Geospiza fortis) population had smaller beaks before the drought? Why? The drought caused small soft seeds to be short in supply. So those with large beaks were able to survive on bigger, harder seeds and thus those are the ones that reproduced.
What is a POPULATION?
all the individuals of a given species in a given area
What are GENES?
A gene is a locus (or region) of DNA that encodes a functional RNA or protein product, and is the molecular unit of heredity
What is GENETIC VARIATION?
differences among individuals in the composition of their genes or other DNA sequences
What is PHENOTYPIC PLASTICITY? What was an example of this from class?
variation in appearance due to environmental influences
ex. the caterpillars (nemoria arizonaria) which look different due to their diets and environments
What are the two ways to measure genetic variation?
- Nucleotide Variability: measured by comparing the DNA sequences of pairs of individuals
- Gene Variability: measured at the whole gene level which is quantified by average heterozygosity
What is GEOGRAPHIC VARIATION? What is an example of this talked about in class?
differences in the genetic composition of separate populations
ex. the house mice of Madera separated by mountains
from the slides: Researchers have observed differences in the karyotypes (chromosome sets) of the isolated populations. Fusion of chromosomes have occurred in both of these isolated populations; however, the patterns of fusion are different in these two population. In the blue population, the chromosome 2.4 is the fusion of chromosomes 2 and 4. In the red population, chromosome 2 has been fused with chromosome 19. Because the chromosome-level changes keep the genes intact, there is no phenotypic differences.
What is a CLINE? What is an example of this talked about in class?
a graded change in character along a geographic axis
ex. The mummichog fish
the frequency for an allele decreases at a steady rate as one observes populations of mummichogs in warmer water
from the slides: the frequency for the allele for the enzyme lactate-dehydrogenase B (which functions in metabolism)decrease fish sampled from Maine to Georgia. This form of the enzyme is a better catalyst in cold water than other versions of the enzyme; thus, individuals with this allele can swim faster in cold water than can individuals with other alleles.
What is a MUTATION? What is an example of a helpful mutation talked about in class?
change in the nucleotide sequence of an organisms DNA
ex. ancestor of mammals had a single genet for detecting odors which has been duplicated many times giving rise to better olfactory sense
What are the four sources of genetic variation?
- new alleles due to mutations
- altering gene number or position through chromosomal changes that disrupt the norm
- rapid reproduction (can increase mutation rates)
- sexual reproduction due to cross over, independent assortment, and fertilization
What are the 5 assumptions of the HW principle of equilibrium?
- no mutations are occurring
- random mating is occurring
- no natural selection is occurring
- extremely large population size
- no gene flow (e/immigration)
What is the HW equation for allele frequencies?
p + q = 1
What is the HW equation for genotype frequencies?
(PxP) + (2xPxQ) + (qxq) = 1
What are the 4 things that can alter allele frequencies?
- natural selection
- gene flow
- genetic drift
- sexual selection
What is GENETIC DRIFT? What is an example of this talked about in class?
a process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
ex. assortment of flowers that quickly turn to all red
Where is GENETIC DRIFT most likely to occur?
in small population
What are the two types of GENETIC DRIFT?
- FOUNDER EFFECT
2. BOTTLE NECK EFFECT
What is the FOUNDER EFFECT? What is an example of this talked about in class?
genetic drift that occurs when a few individuals become isolation from a larger population and form new populations whose gene pool is not reflective of the original population
ex. amish people and genetic tendency to have 6 fingers
What is the BOTTLENECK EFFECT? What is an example of this talked about in class?
genetic drift that occurs when the size of a population is reduced as by natural disaster or human actions, and the remaining population no long represents the original
ex. praire chicken
from the slides: genetic drift resulted in a drop in the number of alleles per locas and a decrease in the percentage of eggs that hatched.
What is the GENE FLOW ? What is an example of this talked about in class?
the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes
ex. PARUS MAJOR (central vs. eastern population) Parus major (Great tits) central population have a lower survival rate on the island than the Eastern population. Scientist found that this lower survival rate was due to a higher rate of gene flow from the mainland to the central population, causing them to have more alleles in the population that were not adapted for island selective pressures.
ex. water snake with bands vs. no bands
the snake with bands does not thrive on the island but does fine on the mainland. one would think that phenotype of the bands would be selected against and eventually disappear on the island but every year snakes from the mainland bring the phenotype over and keep a minority of snakes with bands present in the current population
What is the RELATIVE FITNESS? What is an example of this talked about in class?
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
What are the 3 types of directional national selection?
- Directional
- Disruptive
- Stabilizing
What is Directional Selection? example?
occurs when conditions favor individuals exhibiting one extreme of a phenotypic tang thereby shifting a populations frequency for the radical phenotype
ex. mice living amongst dark rocks (the darkest mice living amongst dark rocks)
What is disruptive selection? example?
favors individuals at both ends of the bell curve of the phenotypic ranges thereby decreasing the population size of the intermediate phenotype?
ex. black bellied seed cracker
soft seeds can be eaten by small billed
hard nuts can be eaten by large billed
neither can be eaten easily by intermediate
What is stabilizing selection? Example?
removes the extreme phenotypes and builds up the population of the intermediate phenotypes
ex. babies birth weight
What is sexual selection?
a process in which individuals w/ certain inherited characteristics are more likely than other individuals of the same sex to obtain a mate
What is INTRASEXUAL SELECTION? example?
selection between the SAME SEX. individuals compete directly for mates
ex. wild mustangs that fight each other
What is INTERSEXUAL SELECTION? example?
(mate choice) individuals of the opposite sex (usually females) are choosey in selecting their mates from the other sex
ex. HUMANs
What is DIMOPHISM? example?
Differences between the secondary sex characteristics of males and females of the same species
ex. peacocks
What are the two biological un-factors of a females sexual preferences?
good heath and good genes
What is BALANCING SELECTION? example?
natural selection that maintains two or more phenotypic forms in a population
What are two ways balancing selection can occur?
- frequency-dependant selection
2. heterozygote advantage
What is FREQUENCY DEPENDENT SELECTION? example?
selection in which the fitness of a phenotype depends on how common the phenotype is in the population
ex. left and right mouthed fish (Perissodus microlepis)
from the PP: Perissodus microlepis are a scale-eating fish in Lake Tanganyika and some are left mouths while other are right mouths. The prey species guards against the side that is most common. Thereofre, form year to year, selection favors which ever mouth is least common. As a result the frequency of left and right-mouthed fish oscillates over time.
What is HETEROZYGOTE ADVANTAGE? example?
When individuals w/ a heterozygous at a particular loci have greater fitness than both homozygous genotypes
ex.
homo recessive- malaria favors
homo dominant- leads to sickle cell
hetero- healthy
What are the 4 main reasons that national selection cannot fashion perfect organisms?
- selection can only act on existing variations
- evolution is limited by historical constraints
- adaptations are often compromises
- chance, natural selection, and the environment interact
