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biology > topic 10 - genetics > Flashcards

topic 10 - genetics Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

why does a second meiotic division occur?

A

sister chromatids separate during meiosis II since meiosis I = diploid –> haploid

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2
Q

what are the stages of meiosis?

A

meiosis I
meiosis II

both of which follow the same stages as mitosis

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3
Q

what happens during meiosis I?

A

diploid –> haploid

P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell

A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell

T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

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4
Q

what happens during meiosis II?

A

separates sister chromatids

P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)

M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator

A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles

T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells

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5
Q

what is the outcome of meiosis?

A

four haploid daughter cells

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6
Q

what is independent assortment?

A

description of how pairs of alleles separate independently from one another during gamete formation

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7
Q

what is meiosis?

A

type of cell division that reduces the number of chromosomes in the parent cells by half and produces four gamete cells

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8
Q

the inheritance of one gene/trait is dependent to the inheritance of any other gene/trait - TRUE OR FALSE?

A

FALSE! It is independent

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9
Q

what is the formula to determine the potential chromosome combinations?

A

2^n (where n = haploid number)

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10
Q

why is there an equal chance of a gamete containing either the maternal or paternal copy of a given chromosome?

A

homologous pairs of chromosomes line up in a random orientation along the equator during Metaphase I

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11
Q

can independent assortment occur if two genes are located on the same chromosome? (linked genes)

A

no

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12
Q

what is synapsis and when does it occur?

A

the process of homologous chromosomes connecting (forming points of connections between nonsister chromatids) // occurs during prophase I of meiosis

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13
Q

what are chiasmata?

A

structure that forms between a pair of homologous chromosomes by crossover recombination and physcially links the homologous chromosomes during meiosis

POINTS OF EXCHANGE

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14
Q

what is a bivalent? or a tetrad?

A

connected homologues (two chromosomes = bivalent, four chromatids = tetrad)

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15
Q

what is crossing over?

A

nonsister chromatids breaking and recombining with their
homologous partners

OR

exchange of genetic material between non-sister homologous chromatids

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16
Q

what can chiasmata formation between nonsister chromatids result in?

A

exchange of alleles

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17
Q

until when are nonsister chromatids physically connected by chiasmata?

A

anaphase

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18
Q

what are recombinant chromosomes?

A

chromosomes that consist of genetic material from both homologues

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19
Q

what can recombination lead to?

A

novel allele combinations

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20
Q

what does crossing over do?

A

increases the genetic diversity of potential offspring

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21
Q

what are unlinked genes?

A

gene loci are on separate chromosomes

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22
Q

why are genes unlinked?

A

random orientatino of homologous pairs during metaphase I of meiosis

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23
Q

what is a dihybrid cross?

A

mating experiment between two organisms that are identically hybrid for two traits

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24
Q

what does a dihybrid cross determine?

A

the genotypic and phenotypic combinations of offspring for two particular genes that are unlinked

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25
Q

what method is used to work out potential gamete combinations in a dihybrid cross?

A

FOIL
First / Outside / Inside / Last

ex. AaBb
AB, Ab, aB, ab

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26
Q

What are the steps to complete a dihybrid cross?

A
  1. designate characters to represent alleles
  2. write the genotype and phenotype of the parents
  3. write down all of the potential gamete combinations
  4. use a punnett square to work out potential genotypes of offsprings
  5. write out the phenotype ratios of potential offspring
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27
Q

what is a linkage group?

A

group of genes whose loci are on the same chromosome and hence don’t independently assort

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28
Q

what is a locus

A

physical location of a gene or other DNA sequence on a chromosome

like genetic street address :)

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29
Q

do linked genes follow the law of independent assortment?

A

NO! they function as a single inheritable unit

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30
Q

who demonstrated the law of independent assortment?

A

mendel // peas!!!

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31
Q

how are linked genes represented?

A

in pairs, vertically (AB / ab)

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32
Q

can linked genes be separated? if so, how

A

yes, through crossing over

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33
Q

do recombinant phenotypes occur more frequently or less frequently?

A

LOWER FREQUENCY as they are only evident when crossing over increases

Frequency increases the further apart two genes are

34
Q

who determined the concept of gene linkage and how

A

Thomas Morgan, fruit fly experiment

35
Q

what is the chi-squared test?

A

statistical measure used to determine whether the difference between an observed and expected frequency distribution is statistically significant

36
Q

what does it mean if the observed frequencies do not conform to the expected frequencies for an unlinked dihybrid cross?

A

genes are linked, inheritance is not random and are potentially affected by natural selection

37
Q

how is a chi-squared test conducted? (STEPS)

A
  1. identify hypothesis
  2. table of frequencies
  3. chi squared formula
  4. degrees of freedom
  5. identify the p value
38
Q

what is the chi squared formula?

A

x^2 = sum of (O-E)^2 / E
where
O = observed frequency
E = expected frequency

39
Q

how are degrees of freedom calculated?

A

df = (m-1)(n-1)
where m = # of rows
n = # of columns

40
Q

what are monogenic traits?

A

characteristics controlled by a single gene locus (finite pattern of expression)

41
Q

what are polygenic traits

A

characteristics controlled by more than two gene loci (bell shaped distribution)

42
Q

polygenic traits can be influenced by the environment: True or False

A

True

43
Q

what are two examples of polygenic traits and how are they effected by the environment?

A

human height: diet

human skin colour: sun exposure

44
Q

what is a gene pool

A

the sum total of alleles for all genes (and alleles) present in a sexually reproducing population

45
Q

what does a large gene pool indicate? what does a small gene pool indicate?

A

large: high amount of genetic diversity
small: low amount of genetic diversity

46
Q

which is preferred? a high amount of genetic diversity or a low amount? why?

A

high amount as it increases the chance of biological fitness and survival

47
Q

what is evolution?

A

cumulative change in the heritable characteristics of a population across successive generations

48
Q

what are the mechanisms of change?

A 
mutation (random change in the genetic composition)
gene flow (movement of alleles into/out of a population)
sexual reproduction (assortative mating)
genetic drift (result of chance or random event changing composition of gene pool)
natural selection (differentially selective environmental pressures)
49
Q

what is the allele frequency?

A

relative proportion of a particular allele within a population

50
Q

what is genetic drift?

A

change in the composition of a gene pool as a result of chance or random events

51
Q

genetic drift is more significant in larger populations: true or false?

A

FALSE, it is more significant in smaller populations where chance events have a bigger impact on the gene pool

52
Q

what the two mechanisms by which a large population is reduced to a small population?

A

population bottlenecks, founder effect

53
Q

what is a population bottleneck?

A

event reduces population size by an order of magnitude around or greater than 50%

can be environmental (ex. fires, floods) or human induced (ex. overhunting)

54
Q

what is the founder effect?

A

small group breaks away from a larger population to colonize a new territory

original population remains intact!!

the new population has less genetic variability (more susceptible to genetic drift)

55
Q

what is natural selectioN?

A

change in the composiiton of a gene pool in response to a differentially selective environenmental pressure

56
Q

what are the three types of natural selection?

A

stabilizing selection
directional selection
disruptive selection

57
Q

what is stabilizing selection (with example)

A

when an intermediate phenotype is favored at the expense of extremes (conditions are stable)

ex. human birth weights (too large = birth complications, too small = high infant mortality)

narrow width of distribtion, gets rid of extreme variations

58
Q

what is directional selection (with examples)

A

when one phenotypic extreme is selected at the cost of the other (when conditions change)

ex. antibiotic resistance (w/ antibiotic, resistance up, no antibiotic = susceptibility up)

shifts distribution left/right, favours ONE extreme

59
Q

what is disruptive selection (with examples)

A

when both extremes are favored at the expense of the intermediate (conditions fluctuate)

ex. moth pigmentation (camouflage, depends on conditions)
favours both extremes
bimodal distribution

60
Q

when does reproduction isolation occur?

A

when barriers prevent two populations from interbreeding

61
Q

what are the two main categories of reproductive isolation barriers?

A

prezygotic isolation (before fertilization)

postzygotic isolation (after fertilization, offspring are not viable or infertile)

62
Q

what are the three main examples of prezygotic isolation barriers?

A

temporal
behavioural
geographic

63
Q

what is temporal isolation?

A

populations have distinct / separate reproductive cycles

64
Q

what is behavioural isolation?

A

populations exhibit or respond to different specific courtships

65
Q

what is geographic isolation

A

populations occupy different habitats / niches in an area

66
Q

what is speciation?

A

evolutionary process that results in the formation of a new species from a pre-existing species

67
Q

when does speciation occur?

A

when reproductive isolating mechanisms prevent two breeding organisms from producing fertile, viable offspring

68
Q

what are the two basic mechanisms via which speciation occurs?

A

allopatric (geographical)

sympatric (reproductive)

69
Q

what is allopatric speciation?

A

geographic!!

physically separated populations are exposed to different environmental conditions and begin to diverge

70
Q

what is sympatric speciation?

A

divergence of species in the same geographic location (due to reproductive isolation)

71
Q

what is sympatric speciation usually caused by?

A

meiotic failure during gamete formations

72
Q

what is polyploidy?

A

heritable condition of posessing more than two complete sets of chromosomes

73
Q

what is polyploidy usually caused by?

A

failure to undergo cytokinesis

74
Q

what is polyploidy most common in?

A

plant species that can self pollinate or reproduce asexually

75
Q

why do farmers want polyploid crops?

A

allows for the production of seedless fruits

usually larger and disease resistant

76
Q

what are the two models of evolution via speciation?

A

phyletic gradualism

punctuated equilibrium

77
Q

what is phyletic gradualism?

A

speciation occurs uniformly (constant pace over a period of time, continuous/gradual accumulation of mutations)

supported by the evolution of the modern horse hoof

78
Q

what is punctuated equilibrium?

A

speciation occurs in rapid bursts with periods of stability (characteristics are maintained if conditions are stable, environmental change promotes rapid divergence)

gaps in the fossil record support this

79
Q

what is the Hardy-Weinberg principle? (definition + equations)

A

means by which the frequency of two alleles can be predicted within a population
p + q = 1
(p+q+^2 = 1

80
Q

what are the population conditions assumed when using the Hardy-Weinberg equation?

A

population is large with random mating
no mutation/gene flow
no natural selection

biology (11 decks)

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