Chapter 18

gene pool

All the genes, including all the different alleles for each gene, that are present in a population

Which of these sentences describe sources and preservation of genetic variation? Select all that apply.

Antibiotic resistance in bacterial populations is caused by natural selection of bacteria that inherit mutations that make them resistant to the antibiotics. If a cell has two pairs of chromosomes, four kinds of gametes are possible as a result of reshuffling of chromosomes during meiosis. Crossing-over causes a shuffling of allele combinations during meiosis as the alleles from each parent form new combinations on homologous chromosomes. When two bacteria are linked during conjugation, the donor cell passes DNA to the recipient cell which causes genetic recombination.

Single gene traits

Dominant vs. recessive

Polygenic traits

Each gene may have two or more alleles. Genes may be on the same chromosome or different chromosomes. A graph of the frequencies of phenotypes often shows a normal distribution.

Single-Gene traits

Each gene may have two or more alleles.Depending on the number of alleles involved, two to three distinct phenotypes are generally observed.All alleles are of the same gene.

speciation

Formation of new species

Several steps led to the evolution of 13 different finch species on the Galápagos Islands. Rearrange the steps that led to the many species of Darwin's finches into the correct order. Place the first step at the top and the final step at the bottom.

Founder finches arrive on one of the Galápagos Islands. A few birds crossed to another island and the two bird populations were now geographically isolated. Changes in gene pools occurred as the bird populations adapted to the specific environment of each island. Differences in beak size and mating behavior probably led to reproductive isolation as some birds crossed back from the second island to the first island. Over time, as these two species lived together on the same island, they evolved in a way that increased the differences between them.

sources of genetic variation

Mutations, Genetic Recombination during sexual reproduction, and lateral gene transfer.

Conditions for evolution to occur

Natural selection favors green beetles, because they are better camouflaged from predators and therefore their alleles will be contributing at higher rates to the next generation. Large numbers of brown beetles were killed in a forest fire and produced genetic drift of certain allele frequencies in the population. Preferred mates are red, so these individuals reproduce at a higher rate and contribute their alleles to the next generation gene pool at a higher frequency. Purple mutants appear among the beetles that will change the allele frequencies in the population. A significant number of yellow beetles left, removing alleles through gene flow out of the population.

During the last Ice Age, deer mice in Michigan became separated by a large glacial lake and are now two different species.Identify the mode of speciation.

Populations were separated through geographical isolation

The Devil's Hole water system is part of a large underground aquifer in Death Valley National Park. After the last Ice Age, around 10,000 years ago, as the water dried up and the land turned to desert, separate pools of water formed. --------of pupfish eventually became isolated in a few of these water holes and springs and then evolved different ----------to become distinct species over time. This kind of ----------likely occurred because each water pool was inhabited by a few surviving individuals of the original larger population. A change in -------- following a large reduction in population size is called a ---------

Populations, adaptive traits, genetic drift, allele frequency, bottleneck effect

Several species of leopard frogs are common throughout North America, where their ranges overlap. Different species of leopard frogs are very similar in appearance, but the males of each species have a unique courtship call. How did speciation most likely occur in leopard frogs?

Reproductive isolation occurred through behavioral isolation.

Darwin's Finches

Speciation in Galapagos finches occurs by founding a new population, geographic isolation changes in new population's gene pool, behavioral isolation, and gene pool

Five closely related species of frogs live in ranges that overlap. Some breed in woodland ponds, some in lowland swamps, and some in streams. How do these five species of frogs remain separate and do not attempt to mate?Study the graph and the text to identify two modes of isolation.

Temporal isolation: The species remain separate because the period of most active mating differs. Geographical isolation: The species remain separate because they have different breeding sites.

What does the Hardy-Weinberg principle state?

That allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change.

What do genes determine?

The number of phenotypes for a trait

The original population of salamanders migrated southward from the north of California. They avoided the Central Valley because it was too dry and hot for them to live there. As they moved south, the eastern and western salamander populations evolved and by the time they got together again in Southern California, they could no longer interbreed and had become two new species of salamanders.Identify the main mode of isolation of eastern and western salamanders in Southern California.

The populations evolved separately because they were geographically isolated.

Conditions for Hardy-Weinberg equilibrium

There should be no migration of beetles into or out of the population so that there is no gene flow that can introduce or remove alleles. The population of beetles must be large enough so that genetic drift is avoided. There should be no natural selection on the beetle population that would favor certain alleles to be contributed at higher rates to the next generation. There should be random mating among beetles, so that no individuals reproduce at a higher rate and contribute their alleles to the next generation gene pool at a higher frequency. No mutations should appear in the beetle population, because new alleles would change the allele frequencies.

Isolation

When populations become reproductively isolated, they can evolve into two or more separate species reproductive isolation can happen in a variety of ways

genetic bottleneck

a change in allele frequency following dramatic reduction in size of population- reduces the amount of diversity of an area (ex. disease)

founder's effect

allele frequencies change as a result of migration of a small subgroup of a population

Darwin's finches were

an example of natural selection, founder effect, and speciation

evolution

any change over a relative amount of time

crossing over

chromosomes move independently during meiosis

polygenic traits

controlled by two or more genes

alleles

different forms of genes

In many animals, height is an example of a polygenic trait. Which types of natural selection can affect polygenic traits?

directional, stabilizing, and disruptive

Hardy-Weinburg Equations

genetic distribution if a population is not evolving allele frequencies in its gene pool do not change

temporal isolation

happens when they reproduce at different times (ex. flowers-they don't open bloom at the same time)

genetic equilibrium

if a population is not evolving, allele frequencies in its gene pool do not change

directional selection

individuals at one end of the curve have higher fitness

stabilizing selection

narrowing toward mid section (butterflies in the middle highest fitness)

Genetic drift

natural disaster that might impact an event, a sequence of events change occurrences can cause an allele to become more or less common in a population

disruptive selection

nature is favoring those on the end, disrupting the curve

conditions that disturb genetic equilibrium

nonrandom mating, small population change, immigration or emigration

mutations

only matters if they're passed from generation to generation- has to occur in sperm or egg cell(the only cells that are passed down)

lateral gene transfer

passing of one gene from one organism to another- can occur between organisms of the same or different species

What does natural selection act on?

phenotype

Behavioral Isolation

populations are able to interbreed to develop differences in courtship rituals(different ways of singsong, way to get mate) Because ways to get mate changed species get confused and don't recognize mating call

geographic isolation

populations separated by barriers such as rivers -these populations cannot get together and breed (ex. valley, grand canyon)

allele frequency

the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene.

If there is no shift

there is no evolution