Chapter 23 Flashcards Preview

AP Biology Semester 1 > Chapter 23 > Flashcards

Flashcards in Chapter 23 Deck (62):
1

micro evolution

the change in allele frequencies in a population over generations

2

what are three things that cause allele frequency change?

-natural selection
-genetic drift
-gene flow

3

what causes adaptive evolution?

natural selection

4

what is essential to have in a population in order for evolution to occur

variation in heritable traits
-you get variation from different genes
-you need a gene to make a certain protein which causes a phenotype
-if you don't have the gene to a trait then you can't have the trait

5

Both ____ and _____ characters contribute to variation within a population

-discrete
-quantitative

6

true or false:
discrete characters can be classified on an either - or basis

true

7

true or false:
quantitative characters vary along a continuum within a population

true

8

average heterozygosity

measures the average percent of loci that are heterozygous in a population

9

how is nucleotide variability measured?

measured by comparing the DNA sequences of pairs of individuals

10

geographic variation

most species exhibit this.
-differences between gene pools of separate populations

11

cline

which is a graded change in a trait along a geographic axis

12

how can new genes and alleles arise?

by mutation or gene duplication

13

what is a mutation?

a change in nucleotide sequence of DNA

14

only mutations in cells that produce _____ can be passed to offspring

gametes

15

what is a point mutation

a change in one base in a gene

16

what are the possible effects of point mutations?

-can be harmless
-mutations in a genes can be neutral because of redundancy in the genetic code
-result in a change in protein production are often harmful
-result in a change in protein production that can sometimes be beneficial

17

what type of chromosomal mutations are typically harmful?

mutations that delete, disrupt, or rearrange many loci

18

what type of chromosomal mutations are less harmful?

duplication of small pieces of DNA increases genome size and is usually less harmful

19

what can shuffle existing alleles into new combinations?

sexual reproduction

20

population

a localized group of individuals capable of interbreeding and producing fertile offspring

21

gene pool

consists of all the alleles for all loci in a population

22

how is a locus fixed?

if all individuals in a population are homozygous for the same allele

23

how can frequency of an allele in a population be calculated for diploid organisms

p + q = 1

24

what is the hardy-weinberg principle

-describes a population that is not evolving
-frequencies of alleles and genotypes in a population remain constant from generation to generation

25

if a hardy weinberg equation is not in equilibrium what does this mean?

-if a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving

26

what equation is used to find the genotypic ratio of alleles?

p^2 + 2pq + q^2 =1
-p is dominant
-2pq is heterozygous
-q is recessive

27

what does the hardy weinberg theorem describe?

a hypothetical population that is not evolving
FYI in real populations, allele and genotype frequencies do change over time

28

what five conditions have to occur for nonevolving populations?

1. No mutations
2. random mating
3. no natural selection
4. extremely large population size
5. no gene flow

29

true or false:
natural populations can evolve at some loci, while being in Hardy-weinberg equilibrium at other loci

TRUE

30

what three major factors alter allele frequencies and bring about most evolutionary change:

-natural selection
-genetic drift
-gene flow

31

genetic drift

describes how allele frequencies fluctuate unpredictably from one generation to the next

32

what does genetic tends to reduce what?

genetic variation through losses of alleles

33

the smaller a sample of population, the greater the chance of____

deviation from a predicted result

34

founder effect

occurs when a few individuals become isolated from a larger population
-allele frequencies in the small founder population can be different from those in the larger parent population

35

bottleneck effect

a sudden reduction in population size due to a change in the environment
-the resulting gene pool may no longer be reflective of the original population's gene pool

36

if the population remains small, it may be further affected by ______

genetic drift

37

what are 4 things to know about genetic drift?

1. significant in small populations
2. causes allele frequencies to change at random
3. can lead to a loss of genetic variation within populations
4. can cause harmful alleles to show up

38

gene flow

consists of movement of alleles among populations
-alleles can be transferred through the movement of fertile individuals or gametes

39

gene flow tends to reduce ______

variation among populations over time

40

gene flow can decrease _____

the fitness of a population

41

gene flow can increase____

the fitness of a population

42

evolution by natural selection involves both _____ and ______

-change
-sorting

43

new genetic variations arise by _____

chance

44

beneficial alleles are sorted and favored by

natural selection

45

how does natural selection bring about adaptive evolution

acting on an organism's phenotype

46

what does survival of the fittest really mean?

reproductive success

47

relative fitness

the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
-selection favors certain genotypes by acting on the phoenotypes of certain organisms

48

directional selection

favors individuals at one end of the phenotypic range

49

disruptive seleciton

favors individuals at both extremes of the phenotypic range

50

stabilizing seleciton

favors intermediate variants and acts against extreme phenotypes

51

natural selection increases _____

frequencies of alleles that enhance survival and reproduction

52

sexual selection

natural selection for mating success

53

sexual dimorphism

marked differences between the sexes in secondary sexual characteristics

54

intrasexual selection

competition among individuals of one sex for mates of the opposite sex
(usually males)

55

intersexual selection

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

56

neutral variation

genetic variation that does not confer a selective advantage or disadvantage

57

how does diploidy maintain genetic variation?

in the form of hidden recessive alleles through heterozygotes

58

balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a populations

59

what does balancing selection include?

-heterozygote advantage
-frequency-dependent selection

60

heterozygote advantage

occurs when heterozygotes have a higher fitness than do both homozygotes
-natural selection will tend to maintain two or more alleles at that locus

61

frequency dependent selection

the fitness of a phenotype declines if it becomes too common in the population
-selection can favor whichever phenotype is less common in a population

62

why can natural selection not fashion perfect organisms? (4)

1. selection can only act on existing variations
2. evolution is limited by historical constraints
3. adaptations are often compromises
4. chance, natural selection, and the environment interact