Chapter 17: Evolution of Populations

Where do new genes come from

-one way in which new genes evolve is through the duplication, and then modification, of existing genes

variation?

-raw material for natural selection

founder effect?

-situation where allele frequencies change as a result of the migration of a small subgroup of a population

what is a current hypothesis about galapagos finches speciation?

-speciation in Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, behavioral isolation, and ecological competition

mutations

-species cannot mutate if it wants to stay at equilibrium -in reality, mutations can introduce new alleles into a gene pool, changing the frequency, causing evolution to occur

nonrandom mating

-species pick individuals to mate with based on heritable traits like size, strength, or coloration called sexual selection -has to be nonrandom for natural selection to occur

what is alleles

-specific forms of a gene that may vary from individual to individual

What determines the number of phenotypes for a given trait

-the number of phenotypes produced for a trait depends on how many genes control the trait

lateral gene transfer:

-the passing of genes from one organism to another organism that is not its offspring

what are the sources of genetic variation?

-the three are mutation, genetic recombination during sexual reproduction and lateral gene transfer

single-gene trait

-trait controlled by only one gene -like a snail band color -thus, it is controlled by two alleles and only two alleles -may only have two or three distinct phenotypes

polygenic traits

-traits controlled by two or more genes -more common than single-gene traits

true or false:modern genes probably descended from a much smaller number of genes in the earliest life forms

-true

allele frequency?

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

directional selection

-one end of the curve has higher fitness than individuals in the middle or other end -direction(shifts parabola)

how may hox genes be involved in evolutionary change

small changes in hox gene activity during embryological development can produce large changes in adult animals

how are phenotypes produced?

- an individual's genotype plus environmental conditions produces this

what did researcher realize about meiosis and fertilization, by themselves, in terms of changing allele frequencies?

- it does not change it

how many gene combinations can be made from 23 pairs of chromosomes

-8.4 million gene combinations

can lateral gene transfer occur between organisms of the same species and organisms of different species?

-Yes! Both!

since members of a population interbreed, they share...?

-a common group of genes, gene pool

how does natural selection affect polygenic traits?

-affects the relative fitness of phenotypes and thereby produces one of three types of selection:directional, stabilizing, or disruptive

what do phenotypes include

-all physical, physiological, and behavioral characteristics of an organism -such as eye color or height

hardy-weinberg principle?

-allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change -predicts using punnett squares but for a population, not individuals

What do scientist study to determine whether a population is evolving?

-allele frequency

mutation?

-any change in the genetic material of a cell

evolution?

-any change over time in the allele frequency in a population

what is an evolutionary adaptation?

-any genetically controlled trait that increases an organism's ability to pass along its alleles

immigration or emigration

-any movement of individuals in or out of a population can cause natural selection -by leaving or entering a population, the gene pool changes

Why does natural selection never act directly on genes?

-because it is an entire organism-not a single gene- that either survives or reproduces or dies without reproducing

bottleneck effect?

-change in allele frequency following a dramatic reduction in the size of a population -can sharply reduce a population's genetic diversity

Different types of mutations:

-changes to individual genes -changes in larger pieces of chromosomes -some are neutral and does not change phenotype

gene pool?

-consists of all the genes, including all the different alleles for each gene, present in a population

species

-defined as a population or group of populations whose members can interbreed and produce fertile offspring

how are phenotypic ratios determined?

-determined by the frequency of alleles in the population as well as by whether the alleles are dominant or recessive

Why do biological family members resemble each other, but also look different?

-differences come from gene shuffling during reproduction and environmental influences. -some are caused by random mutation -look alike because of shared gene pool

What does natural selection act on

-directly on phenotype, not genotype -meaning, natural selection acts on an organism's characteristic, not directly on its alleles

small population size

-does not have major effects in large population but in small ones, genetic drift can strongly affect it. -evolutionary change because of genetic drift happens more easily in small populations -has to be somewhat small for natural selection to occur

How common are mutations?

-each of us is born with roughly 300 mutations that make part of our DNA different from those of our parents -most of them are neutral, one or two can be harmful, and a few are beneficial

How is evolution defined in genetic terms?

-evolution, in genetic terms, involves a change in the frequency of alleles in a population over time

True or false: Bacteria does not swap genes on plasmids

-false; they actually do!

behavioral isolation

-form of reproductive isolation in which two populations develop differences in courtship rituals or other behaviors that prevent them from breeding

speciations

-formation of a new species

what is another evolutionary change that is not natural selection?

-genetic drift

do most heritable differences due from mutations or genetic recombination during sexual reproduction?

-genetic recombination during sexual reproduction

In population, what is studied?

-genetic variation and evolution

population?

-group of individuals of the same species that mate and produce offspring

temporal isolation

-happens when two or more species reproduce at different times -one species of toad mate in early summer and another mates in late summer

what conditions are required to maintain genetic equlibrium

-hard-weinberg predicts that the 5 conditions that can cause evolution to occur and disrupt equilibrium is ~ nonrandom mating, small population size, immigration or emigration, mutations, or natural selection

neutral mutations

-have no effect on phenotype

example of polygenic trait?

-height

What is genetics helps us to understand?

-how heritable variation is caused

genetic equilibrium

-if a population is not evolving, allele frequencies in its gene pool do not change meaning the population reaches this state -cannot logically happen but it is a good hypothetical question to understand evolution

natural selection

-if different genotypes have different fitness, evolution will occur -meaning for equilibrium, everyone has to be genetically the same

what is genetic drift

-in SMALL populations, individuals that carry a particular allele may leave more descendants than other individuals leave, simply by chance -overtime, a series of chance occurrences can cause an allele to become more or less common in a population -thus, it is a random change in allele frequency

Why is lateral gene transfer beneficial?

-it can increase genetic variation in any species that pick up the "new" genes -basically, add more to the gene pool -ex:important in evolution of antibiotic resistance in bacteria -also very important in single-celled organisms (bacteria)

what is an organism's genotype?

-it is the particular combination of alleles it carries

how does natural selection affect single-gene traits?

-leads to change in allele frequencies, thus changes phenotype frequencies straight away

disruptive selection

-looks like a volcano opening so it "disrupts" life -individuals at out end of the curve have higher fitness than individuals near the middle of the curve -acts against those that are average, better for those who are extreme -occurs when natural selection is super strong and last long enough for bell curve to split, meaning it creates two different phenotypes fit for the conditions

gene family

-multiple copies of a duplicated gene can turn into a group of related genes -produce similar but not the same proteins as other family members

every time a molecular clock "ticks", it means that there was just a ________ in the species

-mutation

Important to note:

-natural selection operated on individual organisms, but the changes it causes in allele frequency shows up in the population as a whole

Example: will mutation in skin alleles that produce a nonlethal skin cancer be passed onto the next generation?

-no

does an allele frequency have to deal with whether an allele is dominant or recessive?

-no

Do mutations always matter in evolution?

-no, only if they can be passed from generation to generation -for that to happen, they must occur in the germ line cells that produce either eggs or sperm

since there are more than two genes making a polygenic trait, is it easy to tell the phenotypes from each other

-noap @taylor

what is another name for a bell-shaped curve?

-normal distribution

Do individuals evolve?

-not necessarily, population evolve, not individuals themself

True or false: better suited individuals produce more offspring than the less fit individuals do

-true -organisms with higher fitness pass more copies of their genes to the next generation

molecular clock

-used to compare stretches of DNA to mark the passage of evolutionary time -uses mutation rates in DNA to estimate the time that two species have been involving independently

stabilizing selection

-when individuals near center of curve have higher fitness than individuals at either ends -to remember it: the more average you are, the more stable you are -narrows curve but overall positions stays the same

reproduction isolation

-when populations evolves into two separate species. -can develop in a variety of ways including behavioral, geographic, and temporal isolation

geographic isolation

-when two populations are separated by geographic barriers such as rivers, mountains, or bodies of water, preventing them from breeding

do each chromosome in a pair move independently during meiosis?

-yes

is crossing-over another way in which genes are recombined

-yes:this process during meiosis swaps lengths of DNA at random -it increases the number of genotypes creates in each generation -making each individual phenotype different

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