Biology Chapter 24

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What is genetic drift?

A change in allele frequencies caused by random events

Why are the large finches now living on the Galápagos Islands different from the original source population from a nearby island?

1. The separation of habitats reduced gene flow between the populations. 2. Genetic drift occurred in the two populations. 3. Natural selection favored individuals that were more fit in the new environment.

Which of the following statements about reinforcement is true?

Reinforcement is a type of natural selection.

A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time?

Increased fitness of large-beaked birds, leading to natural selection

Which term is used to describe populations that live close enough to interbreed?


What prevents speciation from occurring in sympatric populations?

Gene flow

Which statements about autopolyploid individuals is true?

They contain more than two haploid sets of chromosomes.

What would be the ploidy of the viable gametes produced by a tetraploid individual if nondisjunction of all chromosomes occurred in meiosis I?


How can an allopolyploid plant become a biologically fit new species?

Nondisjunction event during mitosis

How many chromosomes would be found in an allopolyploid plant if its parents had diploid numbers of 2 and 10, respectively?

Haploid number of 6

_____ is rapid speciation under conditions in which there is little competition.

Adaptive radiation

Mass extinctions create conditions that promote _____.

Adaptive radiation

The appearance of an evolutionary novelty promotes _____.

Adaptive radiation

The different finch species found on the Galápagos Islands probably arose as a result of _____

Adaptive radiation

How long does it take new species to form on Earth?

The time required varies considerably.

Select the correct statement describing sympatric speciation.

Sympatric speciation can occur in a single generation.

According to most paleoanthropologists, which of the following is true?

When modern humans arose, archaic humans disappeared in Africa

If your pituitary gland isn’t functioning properly, which of the following will be affected?

reproduction and growth

What do paleoanthropologists generally believe about genetic findings?

Genetic findings need corresponding fossil evidence to be true.

How do genomes of species change?

By mutations in DNA.


the process by which one species splits into two or more species. Produces life’s diversity


changes over time in allele frequencies in a population


the broad pattern of evolution above the species level

species in Latin means..?

kind of appearance

Biological Species Concept

the primary definition of species. Only refers to organisms who reproduce sexually


a group of populations whose members have the potential to interbreed and produce viable offspring

Reproductive Isolation

existence of biological factors (barriers) that impede members of two species from interbreeding and producing offspring. Blocks gene flow and limits the formation of hybrids


offspring that results from interspecific mating

Prezygotic Barriers

block fertilization from occuring

3 ways prezygotic barriers can act:

1. impeding member of different species from attempting to mate 2. preventing an attempted mating from being completed 3. hindering fertilization if mating completed successfully

What holds the population together genetically?

gene flow

What are the 5 prezygotic barriers?

1. Habitat Isolation 2. Temporal Isolation 3. Behavioral Isolation 4. Mechanical Isolation 5. Gametic Isolation

What are the 3 postzygotic barriers?

1. reduced hybrid viability 2. reduced hybrid fertility 3. hybrid breakdown

Postzygotic Barriers

contribute to reproductive isolation after the hybrid zygote formed

Morphological Species Concept

distinguishes species by body shape / structural features Can be applied to sexual and asexual organisms

Ecological Species Concept

defines species by how they interact with living and nonliving parts of their enviornment. Applies to sexual and asexual organsims

Phylogenetic Species Concept

smallest group of individuals that share a common ancestor

Allopatric (other country) Speciation

gene flow is interrupted when a population is divided into geographically isolated subpopulations.

Sympatric (same country) Speciation

speciation occurs in populations that live in the same geographic area. Is less common than allopatric speciation

When does sympatric speciation occur?

If gene flow is reduced by factors like polyploidy, sexual selection, and habitat differentiation.


when a species originates from an accident during cell division that results in an extra set of chromosomes. Causes sympatric speciation

What organism is polyploidy most common in?

plants. More than 80% of plants today are descended form polyploidy


an individual that has more than 2 sets of chromosomes that were derived from a single species. Can generate reproductive isolation in one generation


a sterile hybrid that changes into a fertile polyploid because of various mechansims Are fertile mating with each other, but can’t mate with the parent

Habitat Differentiation

when a subpopulation exploits a habitat or resource not used by the parent population. Causes sympatric speciation

Hybrid Zone

region in which members of different species meet and mate, producing offspring of mixed ancestry

Problems with hybrids

1. they have poor survival and reproduction rate, meaning they rarely produce viable offspring 2. they rarely pass on alleles to future generations

Where are hybrid zones located?

wherever the habitats of interbreeding species meet

3 outcomes for hybrid zones

1. reinforcement of barriers 2. fusion of species 3. stability


reinforcing reproductive barriers

Fusion of Species

too much gene flow occurs in a hybrid zone between reproducing species that the two species become increasingly alike

When does a hybrid species become stable?

when hybrids continue to reproduce.

How can we determine how long it takes for a new species to evolve?

fossil patterns and studies using morphological data or molecular data

Punctuated Equilibria

periods of inactivity punctuated by sudden change

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