Exam 1

Question 1

What is the general idea of natural selection?

Answer 1

populations of organisms change through time, becoming adapted to their current environmental conditions

Question 2

What are the four traits of natural selection?

Answer 2

1. individuals of a species show variation
2. some of this variation is heritable
3. every generation, some individuals produce more offspring than others due to fitness
4. individuals with certain heritable traits leave the most offspring on average - they are “naturally selected”

Question 3

Define biological fitness

Answer 3

an organism’s ability to survive to reproductive age, find a mate, and produce viable off spring

Question 4

what is the equation for biological fitness

Answer 4

the highest # produced by an individual in the pop.

Question 5

define descent with modification

Answer 5

species change over time through the passing of traits from generation to generation, with variations occurring that can lead to the development of new species, all stemming from a common ancestor

Question 6

How do scientist know that species change over time?

Answer 6

• transitional forms in the fossil record
• documented changes in modern species

Question 7

what are homologies

Answer 7

characteristics shared by species because those species inherited them from a shared ancestor

Question 8

What are example of homologies?

Answer 8

• structural homologies: such as vestigial traits
• developmental homologies: gill pouches and tails
• genetic homologies: amino acid sequences of genes that are very similar

Question 9

what must happen for a trait to become more common over time

Answer 9

allele(s) associated with it must become more common within the population; therefore a change in allele frequency impacts evolution

Question 10

Define alleles

Answer 10

versions of genes

Question 11

define genotypes

Answer 11

combination of alleles possessed by individuals

Question 12

define phenotypes

Answer 12

observable traits

Question 13

allele frequency equation

Answer 13

total # of alleles in the population

Question 14

define gene pool

Answer 14

all the alleles present in a population at a particular time

Question 15

What is the Hardy Weinberg Model?

Answer 15

describes the frequencies of alleles and genotypes in a population that is not evolving

Question 16

when does the HW model occur?

Answer 16

only occurs if meiosis and fertilization occur because the allele and genotype frequencies stay the same from one generation to the next

Question 17

when does the HW principle apply?

Answer 17

• no natural selection
• very large population size
• no migration between the population and other populations
• no mutation
• random mating

Question 18

What are the three types of natural selection

Answer 18

• directional selection
• stabilizing selection
• disruptive selection

Question 19

define directional selection

Answer 19

phenotypes at one end of the range of phenotypes have the highest fitness

Question 20

define stabilizing selection

Answer 20

individuals in the middle of the range of phenotypes have the highest fitness

Question 21

define disruptive selection

Answer 21

individuals at the extreme ends of the range of phenotypes have the highest fitness

Question 22

What does directional selection change?

Answer 22

the average value of a trait

Question 23

what does stabilizing selection do?

Answer 23

reduces the amount of variation in a trait

Question 24

what does disruptive selection do?

Answer 24

increases the amount of variation in a trait

Question 25

why doesn’t selection eliminate variation from populations?

Answer 25

1. environmental conditions are constantly changing
2. recessive alleles are often still present
3. Negative Frequency - dependent selection
4. Heterozygote advantage

Question 26

What is negative frequency dependent selection

Answer 26

• genotypes have a higher fitness when they are rare, not when they are common
• example: may be less visible to predators

Question 27

what is heterozygote advantage

Answer 27

when individuals are heterozygote at a particular locus and they do better than homozygous individuals
- natural selection will act to maintain more than one allele in a population

Question 28

define genetic drift

Answer 28

a change in allele frequency arising through chance, occurs when a population size is small

Question 29

is genetic drift chosen or random ?

Answer 29

random; allele frequency changes are random and not related to any property of the allele

Question 30

what does it mean when a gene is fixed?

Answer 30

when only one allele is present within a population

Question 31

describe the founder effect

Answer 31

when some of the organisms migrate to establish a new population? the new population is likely to have different allele frequencies than the source of the originl population by change

Question 32

describe genetic bottleneck

Answer 32

high mortality strikes individual allele at random.
the bottlenecked population is likely to have a different allele frequency than the original population by change.

Question 33

describe gene flow

Answer 33

the transfer of genetic material (alleles) from one population to another, typically occurring through the movement of individuals between populations, resulting in a change in the gene pool of the receiving population

Question 34

define mutations

Answer 34

rare, random changes that occur from DNA copying errors or when damage to DNA is repaired in a way that causes a change

Question 35

what are the different types of point mutations

Answer 35

1. silent
2. missense
3. nonsense

Question 36

silent mutations

Answer 36

change in nucleotide sequences that does not change the amino