Chapter 23: the Evolutions of Populations

Question 1

What is MICROEVOLUTION and what was the example of it in class?

Answer 1

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.

Question 2

What is a POPULATION?

Answer 2

all the individuals of a given species in a given area

Question 3

What are GENES?

Answer 3

A gene is a locus (or region) of DNA that encodes a functional RNA or protein product, and is the molecular unit of heredity

Question 4

What is GENETIC VARIATION?

Answer 4

differences among individuals in the composition of their genes or other DNA sequences

Question 5

What is PHENOTYPIC PLASTICITY? What was an example of this from class?

Answer 5

variation in appearance due to environmental influences

ex. the caterpillars (nemoria arizonaria) which look different due to their diets and environments

Question 6

What are the two ways to measure genetic variation?

Answer 6

1. Nucleotide Variability: measured by comparing the DNA sequences of pairs of individuals
2. Gene Variability: measured at the whole gene level which is quantified by average heterozygosity

Question 7

What is GEOGRAPHIC VARIATION? What is an example of this talked about in class?

Answer 7

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.

Question 8

What is a CLINE? What is an example of this talked about in class?

Answer 8

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.

Question 9

What is a MUTATION? What is an example of a helpful mutation talked about in class?

Answer 9

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

Question 10

What are the four sources of genetic variation?

Answer 10

1. new alleles due to mutations
2. altering gene number or position through chromosomal changes that disrupt the norm
3. rapid reproduction (can increase mutation rates)
4. sexual reproduction due to cross over, independent assortment, and fertilization

Question 11

What are the 5 assumptions of the HW principle of equilibrium?

Answer 11

1. no mutations are occurring
2. random mating is occurring
3. no natural selection is occurring
4. extremely large population size
5. no gene flow (e/immigration)

Question 12

What is the HW equation for allele frequencies?

Answer 12

p + q = 1

Question 13

What is the HW equation for genotype frequencies?

Answer 13

(PxP) + (2xPxQ) + (qxq) = 1

Question 14

What are the 4 things that can alter allele frequencies?

Answer 14

1. natural selection
2. gene flow
3. genetic drift
4. sexual selection

Question 15

What is GENETIC DRIFT? What is an example of this talked about in class?

Answer 15

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

Question 16

Where is GENETIC DRIFT most likely to occur?

Answer 16

in small population

Question 17

What are the two types of GENETIC DRIFT?

Answer 17

1. FOUNDER EFFECT

2. BOTTLE NECK EFFECT

Question 18

What is the FOUNDER EFFECT? What is an example of this talked about in class?

Answer 18

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

Question 19

What is the BOTTLENECK EFFECT? What is an example of this talked about in class?

Answer 19

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.

Question 20

What is the GENE FLOW ? What is an example of this talked about in class?

Answer 20

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

Question 21

What is the RELATIVE FITNESS? What is an example of this talked about in class?

Answer 21

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

Question 22

What are the 3 types of directional national selection?

Answer 22

1. Directional
2. Disruptive
3. Stabilizing

Question 23

What is Directional Selection? example?

Answer 23

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)

Question 24

What is disruptive selection? example?

Answer 24

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

Question 25

What is stabilizing selection? Example?

Answer 25

removes the extreme phenotypes and builds up the population of the intermediate phenotypes

ex. babies birth weight

Question 26

What is sexual selection?

Answer 26

a process in which individuals w/ certain inherited characteristics are more likely than other individuals of the same sex to obtain a mate

Question 27

What is INTRASEXUAL SELECTION? example?

Answer 27

selection between the SAME SEX. individuals compete directly for mates

ex. wild mustangs that fight each other

Question 28

What is INTERSEXUAL SELECTION? example?

Answer 28

(mate choice) individuals of the opposite sex (usually females) are choosey in selecting their mates from the other sex

ex. HUMANs

Question 29

What is DIMOPHISM? example?

Answer 29

Differences between the secondary sex characteristics of males and females of the same species

ex. peacocks

Question 30

What are the two biological un-factors of a females sexual preferences?

Answer 30

good heath and good genes

Question 31

What is BALANCING SELECTION? example?

Answer 31

natural selection that maintains two or more phenotypic forms in a population

Question 32

What are two ways balancing selection can occur?

Answer 32

1. frequency-dependant selection

2. heterozygote advantage

Question 33

What is FREQUENCY DEPENDENT SELECTION? example?

Answer 33

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.

Question 34

What is HETEROZYGOTE ADVANTAGE? example?

Answer 34

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

Question 35

What are the 4 main reasons that national selection cannot fashion perfect organisms?

Answer 35

1. selection can only act on existing variations
2. evolution is limited by historical constraints
3. adaptations are often compromises
4. chance, natural selection, and the environment interact