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biology > topic 10 - genetics > Flashcards

topic 10 - genetics Flashcards

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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
what method is used to work out potential gamete combinations in a dihybrid cross?
FOIL First / Outside / Inside / Last ex. AaBb AB, Ab, aB, ab
26
What are the steps to complete a dihybrid cross?
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
27
what is a linkage group?
group of genes whose loci are on the same chromosome and hence don't independently assort
28
what is a locus
physical location of a gene or other DNA sequence on a chromosome like genetic street address :)
29
do linked genes follow the law of independent assortment?
NO! they function as a single inheritable unit
30
who demonstrated the law of independent assortment?
mendel // peas!!!
31
how are linked genes represented?
in pairs, vertically (AB / ab)
32
can linked genes be separated? if so, how
yes, through crossing over
33
do recombinant phenotypes occur more frequently or less frequently?
LOWER FREQUENCY as they are only evident when crossing over increases Frequency increases the further apart two genes are
34
who determined the concept of gene linkage and how
Thomas Morgan, fruit fly experiment
35
what is the chi-squared test?
statistical measure used to determine whether the difference between an observed and expected frequency distribution is statistically significant
36
what does it mean if the observed frequencies do not conform to the expected frequencies for an unlinked dihybrid cross?
genes are linked, inheritance is not random and are potentially affected by natural selection
37
how is a chi-squared test conducted? (STEPS)
1. identify hypothesis 2. table of frequencies 3. chi squared formula 4. degrees of freedom 5. identify the p value
38
what is the chi squared formula?
x^2 = sum of (O-E)^2 / E where O = observed frequency E = expected frequency
39
how are degrees of freedom calculated?
df = (m-1)(n-1) where m = # of rows n = # of columns
40
what are monogenic traits?
characteristics controlled by a single gene locus (finite pattern of expression)
41
what are polygenic traits
characteristics controlled by more than two gene loci (bell shaped distribution)
42
polygenic traits can be influenced by the environment: True or False
True
43
what are two examples of polygenic traits and how are they effected by the environment?
human height: diet | human skin colour: sun exposure
44
what is a gene pool
the sum total of alleles for all genes (and alleles) present in a sexually reproducing population
45
what does a large gene pool indicate? what does a small gene pool indicate?
large: high amount of genetic diversity small: low amount of genetic diversity
46
which is preferred? a high amount of genetic diversity or a low amount? why?
high amount as it increases the chance of biological fitness and survival
47
what is evolution?
cumulative change in the heritable characteristics of a population across successive generations
48
what are the mechanisms of change?
``` 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
what is the allele frequency?
relative proportion of a particular allele within a population
50
what is genetic drift?
change in the composition of a gene pool as a result of chance or random events
51
genetic drift is more significant in larger populations: true or false?
FALSE, it is more significant in smaller populations where chance events have a bigger impact on the gene pool
52
what the two mechanisms by which a large population is reduced to a small population?
population bottlenecks, founder effect
53
what is a population bottleneck?
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
what is the founder effect?
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
what is natural selectioN?
change in the composiiton of a gene pool in response to a differentially selective environenmental pressure
56
what are the three types of natural selection?
stabilizing selection directional selection disruptive selection
57
what is stabilizing selection (with example)
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
what is directional selection (with examples)
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
what is disruptive selection (with examples)
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
when does reproduction isolation occur?
when barriers prevent two populations from interbreeding
61
what are the two main categories of reproductive isolation barriers?
prezygotic isolation (before fertilization) postzygotic isolation (after fertilization, offspring are not viable or infertile)
62
what are the three main examples of prezygotic isolation barriers?
temporal behavioural geographic
63
what is temporal isolation?
populations have distinct / separate reproductive cycles
64
what is behavioural isolation?
populations exhibit or respond to different specific courtships
65
what is geographic isolation
populations occupy different habitats / niches in an area
66
what is speciation?
evolutionary process that results in the formation of a new species from a pre-existing species
67
when does speciation occur?
when reproductive isolating mechanisms prevent two breeding organisms from producing fertile, viable offspring
68
what are the two basic mechanisms via which speciation occurs?
allopatric (geographical) | sympatric (reproductive)
69
what is allopatric speciation?
geographic!! physically separated populations are exposed to different environmental conditions and begin to diverge
70
what is sympatric speciation?
divergence of species in the same geographic location (due to reproductive isolation)
71
what is sympatric speciation usually caused by?
meiotic failure during gamete formations
72
what is polyploidy?
heritable condition of posessing more than two complete sets of chromosomes
73
what is polyploidy usually caused by?
failure to undergo cytokinesis
74
what is polyploidy most common in?
plant species that can self pollinate or reproduce asexually
75
why do farmers want polyploid crops?
allows for the production of seedless fruits usually larger and disease resistant
76
what are the two models of evolution via speciation?
phyletic gradualism | punctuated equilibrium
77
what is phyletic gradualism?
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
what is punctuated equilibrium?
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
what is the Hardy-Weinberg principle? (definition + equations)
means by which the frequency of two alleles can be predicted within a population p + q = 1 (p+q+^2 = 1
80
what are the population conditions assumed when using the Hardy-Weinberg equation?
population is large with random mating no mutation/gene flow no natural selection

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