Exercise 1

Question 1

What evolve?

Answer 1

populations

Question 2

what four things cause evolution?

Answer 2

1) natural selection
2) genetic drift
3) gene flow
4) mutation

Question 3

what is the HW principle?

Answer 3

gives mathematical proof that allele frequencies do not change from generation to generation in diploid, sexually reproducing populations simply as a result of sexual reproduction and recombination

Question 4

what 5 conditions must be true in order for a population to be in HW equilibrium?

Answer 4

1) large population size
2) no gene flow (immigration/emigration)
3) no net mutations
4) random mating
5) no natural selection

Question 5

what is natural selection?

Answer 5

the process in which organisms with certain inherited characteristics are more likely to survive and reproduce than organisms with other characteristics

Question 6

what happens if a population is in HW equilibrium?

Answer 6

no change in allelic frequencies

Question 7

what’s the point of HW if the conditions are basically never met?

Answer 7

it represents a null model against which we can test observations to see whether evolution is occurring

Question 8

if there are 600 roaches, how many alleles are in the population?

Answer 8

1200

each individual has two alleles

Question 9

in a population of 600 roaches, 900 are A. what is the allelic frequency of A? a?

Answer 9

F(A) = 900/1200 = .75 –> p

F(a) = 300/1200 = .25 –> q

p + q = 1

Question 10

what is F(A) or F(a)?

Answer 10

The allelic frequency

Question 11

how do you find the genotypic frequencies?

Answer 11

p^2 + 2pq + q^2 = 1

Question 12

what does p^2 represent?

Answer 12

the likelihood of receiving A from both parents

the expected frequency of the AA genotype among offspring

Question 13

what does q^2 represent?

Answer 13

the likelihood of receiving the aa genotype

Question 14

what does 2pq represent?

Answer 14

the likelihood of receiving the Aa genotype

Question 15

what did HW show?

Answer 15

sexual reproduction has no effect by itself on allele frequencies

F(A) = p in the next generation –> the proportion of A is the same as the parental population

F(a) = q also

Question 16

how do you find the number of homozygous dominant individuals if you know that p=.75?

Answer 16

so you know that the genotypic frequency of AA is p^2 =(.75)^2 = 0.5625

to find the actual # of homozygous dominant individuals you multiple the frequency by the population size to get (.5625)(600) = 336

Question 17

what is genetic drift?

Answer 17

through random chance, gene frequencies change from generation to generation even when all HW assumption (except infinite population size) are satisfied

most noticeable in small populations

Question 18

what are two types of genetic drift that occur when a population is greatly reduced but then recovers to a greater size?

Answer 18

1) founder effect

2) population bottleneck

Question 19

what is the founder effect?

Answer 19

when a few individuals from an original population disperse and inhabit a new area

the genetics of these few individuals will be passed on to all the offspring in the newly inhabited area and therefore the genetic diversity of this population will be less comprehensive compared the the original population

Question 20

what is a population bottleneck?

Answer 20

occurs when a population is greatly reduced but then recovers

because relatively few individuals survive the bottleneck they pass on their less diverse genetic diversity on to the rest of the growing population

ex. cheetahs

Question 21

what is essential for evolution?

Answer 21

variation

Question 22

what is phenotypic plasticity?

Answer 22

where physical traits vary among individuals based on individual pressures, not on genotype

ex. the lizards that are white and hatched on sand beaches are moved to black lava beds develop dark coloration

Question 23

in the experiment, why were the frequencies obtained in the first generation might have deviated somewhat from the original .5 values?

Answer 23

the cause of the deviation is due to the small gene pool which causes greater deviation in the frequency of the alleles

Question 24

would the deviation from the original frequencies be larger or smaller if more than 25 individuals were drawn per generation for an infinite number of generations?

Answer 24

the deviation would be smaller because of the bigger population

like the odds when flipping a coin

Question 25

why do zoologists encourage sharing threatened and endangered animals among different zoos as breeding partners rather than breeding only the animals within their own zoo?

Answer 25

they want to increase genetic variation and make sure than not only a certain set of alleles will become common and decrease variation

decreased variation could eventually cause evolution of the species to stop

interbreeding would prevent this from happening because new alleles are being presented into population through genetic drift –> not sharing animals decreases the effect of genetic drift

Question 26

Why do blood types vary between locations and/or cultures?

Answer 26

the centralized location of certain blood types is the result of population isolation and lack of genetic drift for many generations

the lack of allele variation causes the percent of the population of a certain to have high frequency of on particular blood type

Question 27

what is a fixed allele?

Answer 27

genetic drift sometimes causes an allele to become fixed, meaning it is the only allele left in the population

Question 28

if an allele is fixed what influence can natural selection can have on its frequency?

Answer 28

if an allele is fixed, it’s the only allele in the gene pool and natural can’t occur

no variation = no evolution