Evolution - Chapter 8

Question 1

Microevolution

Answer 1

microevolution = changes in allele frequencies and phenotypic traits within a population and species
not all evolutionary changes are the result of natural selection
evolution can occur due to catastrophic event

Question 2

Natural selection

Answer 2

organisms that are homozygous for harmful alleles are less likely to survive and produce offspring than those that do not carry such genes
desirability of alleles depends on the local environment
harmful alleles do not disappear over time due to recurring mutations and the presence of heterozygous individuals

Question 3

Stabilizing selection

Answer 3

intermediate phenotypes are favoured, and the traits that lie outside the norm are selected against
improves adaptation of the population to aspects of the environment that stay constant
example = human birth weight

Question 4

Disruptive selection

Answer 4

both extreme phenotypes are favoured
example = british land snails can have dark or light shells, both forms can camouflage in their habitat, but the intermediate forms are most likely to be eaten by birds

Question 5

Directional selection

Answer 5

one extreme phenotype is favoured
shift away from current average condition due to environment change, or new to environment
example = peppered moth

Question 6

Sexual selection

Answer 6

males of some species often acquire frivolous characteristics to impress females
leads to sexual dimorphism (physical differences in appearance of males and females)

Question 7

Genetic drift

Answer 7

change in the frequency of alleles due to random events
in small populations, the likelihood of losing certain alleles due to random/chance events is much higher than in large populations

Question 8

Bottleneck effect

Answer 8

occurs when a population is subjected to near extinction
chance alone may determine which individuals survive the unfavourable times
many alleles are lost from the population, so the genetic makeup of future generations will be limited to the alleles carried by the survivors

Question 9

Founder effect

Answer 9

when a few individuals from a large population establish a new population
alleles are found at a different frequency in an isolated population
the smaller the founding group, the less likely it will represent the genetic makeup of the original population

Question 10

Gene flow

Answer 10

can increase variation in a population by introducing novel alleles from some other populations
unlike genetic drift, gene flow tends to reduce differences within populations

Question 11

Mutations

Answer 11

may be small changes to a gene, or larger changes to a chromosome
larger duplications can lead to sections of the chromosome that are free to mutate and gain new function, as their original function is already taken care of

Question 12

Speciation

Answer 12

the formation of a new species
isolation of a group of individuals from the whole population and a long period of time are key
most common forms of isolation are reproductive or geographic

Question 13

Reproductive isolation

Answer 13

biological factors prevent two populations from interbreeding, despite sharing the same region or habitat
prezygotic isolation prevents gametes from ever meeting
postzygotic isolation prevents maturation and/or reproduction in offspring

Question 14

Prezygotic isolation

Answer 14

ecological or habitat isolation 
seasonal isolation 
behavioural isolation 
mechanical isolation 
physiological isolation
gametic mortality isolation

Question 15

Postzygotic isolation

Answer 15

zygotic mortality
hybrid inviability
hybrid sterility
hybrid breakdown

Question 16

Geographical isolation

Answer 16

when a single population of a species is separated into two or more isolated populations
2 modes of speciations based on geographical relationship of the new species to its ancestral species

Question 17

Allopatric speciaion

Answer 17

speciation as a result of geographical isolation

gene flow is blocked by a geographical barrier

Question 18

Sympatric speciation

Answer 18

speciation while still sharing the same geographical area

gene flow is blocked by genetic change

Question 19

Divergent

Answer 19

species that were once similar diverge or become increasingly distinct
different selective pressures or random genetic flow
when divergent evolution occurs rapidly, it is called adaptive radiation

Question 20

Convergent

Answer 20

similar traits arise because different species have independently adapted to similar environmental conditions
examples = bats and birds, ostriches and emus

Question 21

Co-evolution

Answer 21

the evolution of one species influences another

can lead to dependence of one species on the other

Question 22

Macroevolution

Answer 22

large scale evolutionary change significant enough to warrant the classification of groups into genera or even higher taxa level
example = Cambrian explosion
2 major theories exist for macroevolution

Question 23

Theory of gradualism

Answer 23

the accumulation of many small and ongoing changes and processes
when new species first evolve, they appear very similar to the original species and only become more distinctive as natural selection and genetic drift act on both species
one would expect then to find many transitional species in the fossil record
lack of transitional species is explained by an incomplete fossil record, and the possibility that intermediate forms were not preserved

Question 24

Theory of punctuated equilibrium

Answer 24

relatively rapid spurts of change followed by long periods of little or no change
species evolve very rapidly in evolutionary time
speciation usually occurs in small isolated populations and thus intermediate fossils are very rare
after the initial burst of evolution, species do not change significantly over long periods of time

Question 25

Theory that is used today

Answer 25

both gradual and rapid evolutionary processes are at work, as both are needed to understand the fossil record
before a major extinction event, an environment may be host to many well adapted species, so evolutionary change would be slow
environmental crisis results in extinction of many species, leaving many niches empty
surviving species experience disruptive selection
once they become well adapted, stabilizing selection restarts

Question 26

Traits that have contributed to human success

Answer 26

complex reasoning and communication
ability to learn and use tools
large brain
bipedalism
hands that are capable of coordination

Question 27

Clues on the evolution of humans

Answer 27

skulls = demonstrates brain capacity (intelligence), the memory functions and communication abilities
hip bones = demonstrates the shift to bipedalism, a more energy efficient way of walking for long distances
stone tools = demonstrates the beginning of use of technology, improved eating/hunting abilities
footsteps = demonstrates that human ancestors walked upright long before they had large brains

Question 28

Darwinian medicine

Answer 28

use of evolutionary theory to understand medicine
a fever is an evolved response to help fight off infection = taking a drug to lower body temperature might be unwise
coughing is an evolved mechanism to expel disease-causing organisms from lungs = taking medication that suppresses coughs might not be helpful

Question 29

Hardy-Weinberg problems

Answer 29

allele frequencies will remain constant as long as =
no mutations occur in the alleles
alleles do not migrate into or out of the population
the population is large
mating is random
all possible offspring are equally like to survive