Campbell: Biology Chapter 23 Flashcards

What mechanisms can cause the evolution of populations?

changes in the allele frequencies of a population over time due to either natural selection, genetic drift, or gene flow

give an example of evolution due to natural selection

there was a seed shortage in Daphne Major.

larger beaked birds that could eat the more plentiful large seeds survived at a higher rate

they had a higher fitness

the offspring of the survivors tended to have large beaks and therefore the average beak depth increased in the next generation

Define microevolution

the change in allele frequencies in a population over generations, is evolution at its smallest scale

again, what three mechanisms cause allele frequency change?

natural selection (adaptation to the environment)

genetic drift (chance events that alter allele frequencies)

gene flow (transfer of alleles between populations)

define allele

a variation of a gene

what is needed for evolution by natural selection to occur?

genetic variation

define genetic variation

refers to the differences in genes or ither DNA sequences among individuals

define phenotype

the product of an inherited genotype and environmental influences

the physical, outside effects of the genotype

define genotype

the sequence of the specific genes

i.e. Bb, BB, or bb

how does genetic variation originate?

it originates when new genes and alleles arise by: mutation gene duplication or other processes

genetic variations are produces rapidly in organisms with ______________

short generation times

sexual reproduction can produce genetic variation by______________

recombining existing alleles (crossing over)

define mutation

a change in the nucleotide sequence of DNA

what are 2 ways mutations can occur?

through replication errors or exposure to certain types of radiation or chemicals

Most mutations that alter phenotype are at least _______________

slightly harmful

point mutations in noncoding regions usually cause ___________

neutral variation

in multicellular organisms, only ________________ are passed to offspring

mutations in cell lines that produce gametes

if duplicated genes persist over generations ________ and __________ may arise

mutations can accumulate, new functions

one key potential source of genetic variation

duplication of small segments of DNA

define neutral variation

usually caused by point mutations in the noncoding regions

no selective advantage or disadvantage

in multicellular organisms, only mutations in _______ are passed to offspring

give four examples of large chromosomal mutations

duplication, deletion, inversion, translocation

give an example of a genetic mutation that was highly beneficial

P53 gene. it Identifies cells that are at risk for developing cancer

elephants have extra copies and therefore have significantly lower chances of cancer

mutation rates are ____ in animals and plants

low

mutations can ______ in viruses due to _______

accumulate rapidly, to short generation times and rapid mutation rates

examples of high mutation rate in HIV and why?

drug resistance in HIV because they have a short generation time of about two days

HIV's RNA genome lacks repair mechanisms to catch mutations

what is the main cause of genetic variation in sexually reproducing organisms?

the recombination of alleles

give three mechanisms that create new combinations of existing alleles

1. crossing over (occurs in meiosis)

2. Independent assortment (also occurs in meiosis)

3. Fertilization

what does "crossing over" refer to?

the exchange of genetic material between homologous chromosomes during meiosis

what is independent assortment?

the random distribution of chromosomes into gametes during meiosis

what is fertilization

the random combination of gametes

in which stage does crossing over occur?

during prophase 1 of meiosis

what is the Hardy- Weinberg equation used for?

to test for evolution in a population

what two things are required for a population to evolve?

genetic variation and a factor that causes evolution

What is a population?

all the individuals of the same species that live in the same area at the same time and interbreed and produce fertile offspring

define gene pool

all the possible alleles that exist in a population

a locus is fixed if _____________________________

all individuals in a population are homozygous for the same allele

how do you calculate genotype frequencies?

divide the number of individuals of each genotype by the total number of individuals in the population

how do you calculate the number of copies of each allele in a population?

(# of individuals with homozygous genotype x 2) + # of individuals with heterozygous genotype

nonrandom mating can affect genotype frequencies but not _______ frequencies

allele

define natural selection

differential success in survival and reproduction based on certain heritable traits.

those with traits better suited to their environment produce more offspring than others

natural selection can cause adaptive evolution which is?

a process in which traits that enhance survival or reproduction increase in frequency over time

define genetic drift

the process in which chance events cause allele frequencies to fluctuate unpredictably from one generation to the next

the smaller the sample, the _____ the chance of random deviation from a predicted result

greater

genetic drift tends to ___________ through the random loss of allels

reduce genetic variation

what is the founder effect?

when a few individuals become isolated from a larger population

define the bottleneck effect

when there is a drastic reduction in population size due to a sudden change in the environment

the resulting gene pool may no longer be reflective of the original population's gene pool

Genetic drift summary:

genetic drift is significant in _____ populations

it can cause the ________ to change at __________

it can lead to a loss of ________ within populations

it can cause _________ to become fixed

small

allele frequencies, random

genetic variation

harmful alleles

define gene flow

the movement of alleles among populations

gene flow tends to ______ variation among populations over time and can mitigate the effects of _________

reduce, natural selection

only ________ consistently increases the frequencies of alleles that provide reproductive advantage

natural selection

define relative fitness

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

what are the three ways that natural selection can alter the frequency distribution of heritable traits?

directional selection, disruptive selection, stabilizing selection

define directional selection

favors individuals at one extreme end of the phenotypic range

define disruptive selection

favors individuals at both extremes of the phenotypic range

Define stabilizing selection

favors intermediate variants and acts against extreme phenotypes

natural selection __________ the frequencies of alleles that enhance survival and reproduction

define sexual selection

the process in which individuals with certain heritable traits are more likely to obtain mates than other individuals of the same sex

define sexual dimorphism

a difference in secondary sexual characteristics between the sexes

i.e. different colors, sizes, and behaviors between males and females

define intrasexual selection

the direct competition among individuals of one sex

(often males) for mates of the opposite sex

define intersexual selection

(mate choice) occurs when individuals of one sex (usually females) are choosy in selecting their mates

female choice is often dependent on the male's _______________ and although ________ can can increase the likelihood of mating, it can also ______ the chances of survival

appearance or behavior, showiness, decrease

define frequency - dependent selection

the fitness of a phenotype depends on how common it is

define heterozygote advantage and give an example

when heterozygotes have a higher fitness than both kinds of homozygotes

i.e. sickle cell disease

how does sickle cell disease happen?

a point mutation in the sickle cell allele changes one amino acid, causing improper protein folding, and binding of the proteins into chains forming a fiber

the abnormal hemoglobin fibers distort the red blood cell into a sickle shape in low oxygen conditions