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Genetics BSC-315 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

The further apart two genes are, the greater the probability of

A

recombination

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2
Q

What are synthetic genes?

A

genes located on the same chromosome

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3
Q

When genes on the same chromosome are completely linked, the test cross results in only two possible genotypes in progeny, and these are

A

parental phenotypes

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4
Q

__ __ leads to separation of linked genes

A

crossing over

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5
Q

Departure from 1:1:1:1 ratio of F1 gametes in dihybrid cross indicates

A

linkage

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6
Q

__ __ always most numerous or equal to recombinant

A

parental classes

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7
Q

__ __ are never >50% of total F2 progeny

A

recombinant classes

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8
Q

Crossing over is a random event that will only result in ___ if genes are independently assorting

A

equivalent parental and recombinant phenotype ratios

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9
Q

Recombinant gametes are __ __ than parental gametes when genes are linked

A

less frequent

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10
Q

What is recombination?

A

the reciprocal exchange as a result of crossing-over during meiosis

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11
Q

What is terminalization?

A

movement of chiamata

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12
Q

What happens during anaphase?

A

chromosome separation occurs after chiasmata reach the telomeres

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13
Q

What are the products of anaphase?

A

two recombinant and two parental gametes

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14
Q

Dihybrid test cross of independently assorting genes produces a ___ progeny ratio

A

1:1:1:1

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15
Q

Dihybrid test cross of completely linked genes produces a __ progeny ratio

A

1:1

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16
Q

Dihybrid test cross of genes on same chromosome that are sometimes but not always separated by crossing over in meiosis produce

A

intermediate progeny ratios

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17
Q

1 percent recombination =

A

1 RF (recombination frequency) = 1 map unit (m.u.) = 1 centiMorgan (cM)

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18
Q

In linked genes, parents __ recombinants

A

>

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19
Q

In unlinked genes (exhibit independent assortment), parents __ recombinants

A

=

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20
Q

Linked genes must be __ and __ so that they do not assort independently

A

syntenic; sufficiently close together or on the same chromosome

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21
Q

Independent assortment (unlinked genes) occurs wither when genes are on __ or when they are __

A

different chromosomes; sufficiently far apart on the same chromosome

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22
Q

We can use recombination frequencies from __ for pairs of genes to establish relative gene position

A

two-point crosses

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23
Q

Genes chained together by linkage relationships form a

A

linkage group

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24
Q

Linkage group =

A

chromosome = 1 DNA molecule

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25
Q

Order of genes revealed by genetic mapping corresponds to

A

the actual order of genes along the chromosome

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26
Q

Recombination frequency becomes a less precise estimator of genetic distance at

A

large physical distances

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27
Q

What limits the correspondence between map and physical distance?

A
  • double, triple, and more crossovers
  • 50% limit on observable recombination frequency
  • non-uniform recombination frequency across chromosomes
  • mapping functions compensate some inaccuracies
  • recombination rates differ between species and across genome (recombination hotspots)
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28
Q

Genes close together on the same chromosome are __ and __

A

linked; do not assort independently, they segregate together

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29
Q

Linked genes lead to a __ number of parental class progeny than expected in independent assortment

A

larger

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30
Q

The mechanism of recombination is

A

crossing over

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31
Q

__ are the visible signs of crossing over

A

chiasmata

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32
Q

The further away genes are the __ the opportunity for chiasmata to form between them

A

greater

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33
Q

Recombination frequencies reflect

A

physical distance between genes

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34
Q

Recombination frequencies between two genes vary from

A

0% to 50%

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35
Q

Deviations from 1:1:1:1 ratios can represent

A

chance events or linkage

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36
Q

Chi squared tests evaluate

A

deviation from expected values and the probability that the data fit the expected outcome

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37
Q

What does the null hypothesis state?

A

observed values are no different from expected values

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38
Q

For chi square tests, low p values show __ and high p values show __

A

little deviation from expected; significant deviation from expected

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39
Q

Can a chi-square test prove linkage?

A

no, only provides a quantitative measure of the likelihood that the data can be explained by a hypothesis

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40
Q

All of the genetics functions of DNA depend on

A

specialized proteins that “read” the info in DNA sequence

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41
Q

DNA is localized almost exclusively within

A

chromosomes

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42
Q

DNA contains four kinds of __ linked in a long chain

A

nucleotides

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43
Q

What are phosphodiester bonds?

A

covalent bonds joining adjacent nucleotides

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44
Q

What is a polymer?

A

linked chain of subunits

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45
Q

DNA is made of only __ different subunits

A

4

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46
Q

Protein is made of __ different subunits

A

20

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47
Q

DNA is a __ structure with __ diameter

A

helical; 20 A

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48
Q

Spacing between repeating units in DNA is

A

3.4 A

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49
Q

The DNA helix undergoes a complete turn every

A

34 S

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50
Q

What are the 4 nitrogenous bases of DNA

A

adenine, guanine, cytosine, thymine

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51
Q

What are the ratios of nitrogenous bases?

A

A:T ratio is 1:1, G:C ratio is 1:1

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52
Q

What are DNA’s chemical constituents?

A

deoxyribose, phosphate, 4 nitrogenous bases

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53
Q

What are the purines?

A

adenine and guanine

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54
Q

What are the pyrimidines?

A

thymine and cytosine

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55
Q

The attachment of base to a sugar makes a

A

nucleoside

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56
Q

The addition of phosphate to a nucleoside makes a

A

nucleotide

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57
Q

Nucleotides are linked together in a __ chain in the DNA molecule

A

5’-3’

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58
Q

Phosphodiester bonds always form covalent link between

A

3’ carbon of one nucleotide and 5’ carbon of the next nucleotide

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59
Q

Base pairs consist of __ bonds between a purine and a pyrimidine (G with C, A with T)

A

hydrogen

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60
Q

Each base pair has the same

A

shape (can fit together without disrupting shape of chain)

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61
Q

The strands of DNA are

A

antiparallel (one is 5’-3’ going up-to-down, while other is 3’-5’ going up-to-down)

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62
Q

In a double helix of DNA, sugar phosphate backbones are

A

on the outside

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63
Q

In a double helix of DNA, base pairs are

A

in the middle

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64
Q

The double helix of DNA is two chains held together by

A

hydrogen bonds between A-T and G-C base pairs

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65
Q

How does DNA carry information?

A

base sequence of A,T,C, and G’s

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66
Q

How is the information DNA carries coped for transmission to future generations?

A

DNA replication

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67
Q

What mechanisms allow genetic information to change?

A
  • recombination

- mutations

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68
Q

How does DNA-encoded info govern the expression of phenotype?

A

gene functions

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69
Q

Most genetic info is “read” from

A

unwound DNA

e.g. synthesis of DNA or RNA

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70
Q

Some genetic info is accessible within

A

double-stranded DNA

e.g. DNA- binding proteins that regulate gene expression can access chemical info from “grooves” of DNA helix

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71
Q

What are the 3 possible models of DNA replication?

A
  • semiconservative (Watson-Crick model)
  • conservative
  • dispersive
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72
Q

What is the conservative model of DNA replication?

A

parental double helix remains intact, both strands of daughter helices are newly synthesized

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73
Q

What is the dispersive model of DNA replication?

A

both strands of both daughter helices contain original and newly synthesized DNA

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74
Q

What does the model of DNA replication postulated by Watson and Crick state?

A
  • unwinding of double helix exposes bases on each strand
  • each strand can as a template for synthesis of new strands
  • new strand forms by insertion of complementary base pair
  • single double helix becomes two identical daughter double helices
  • replication is semiconservative: each new molecule contains 1 parent strand and one newly synthesized strand
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75
Q

Energy for DNA synthesis comes from

A

high-energy phosphate bonds associated with dNTPs (deoxynucleotide triphosphates (dATP; dGTP; dTTP; dCTP))

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76
Q

__ __ catalyzes new phosphodiester bonds

A

DNA polymerase

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77
Q

What happens during initiation of DNA replication?

A

proteins open up the double helix and prepare it for complementary base pairing

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78
Q

What happens during elongation of DNA replication?

A

proteins connect the correct sequence of nucleotides on newly formed DNA strands

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79
Q

What are the 3 strict requirements for DNA polymerase action?

A
  • 4 dNTPs (for incorporation into chain and energy)
  • primer with exposed 3’ hydroxyl***
  • single-stranded template DNA (may be unwound by other proteins)
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80
Q

DNA synthesis ALWAYS proceeds in the __ direction

A

5’ to 3’

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81
Q

Template and newly synthesized strands are

A

antiparallel

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82
Q

Initiation begins at the

A

origin (Ori) of replication

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83
Q

What happens in the process of initiation?

A
  • initiator protein binds to Ori (origin of replication)
  • helicase unwinds the helix
  • two replication forks are formed: replication proceeds in both directions
  • single-strand binding proteins keep the DNA helix open
  • primase synthesizes RNA primer (RNA uses U instead of T)
  • primers are complementary and antiparallel to each template strand
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84
Q

What happens in the process of elongation in DNA replication?

A
  • the correct nucleotide sequence is copied from template strand to newly synthesized strand of DNA
  • DNA polymerase III catalyzes phosphodiester bond formation between adjacent nucleotides (polymerization)
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85
Q

Leading strand of DNA synthesis has __ synthesis

A

continuous

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86
Q

Lagging strand of DNA synthesis has __ synthesis

A

discontinuous

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87
Q

What is an Okazaki fragment?

A

short DNA fragment on lagging strand

88
Q

DNA polymerase moves along the template in the __ direction

89
Q

What does DNA polymerase I do?

A

replaces RNA primer with DNA sequence

90
Q

What does DNA ligase do?

A

covalently joins successive Okazaki fragments together

91
Q

There are __ replication forks for each origin of replication

92
Q

DNA can be __ or __; __ or __-stranded

A

linear, circular; double, single

93
Q

In replication of a circular bacterial chromosome, replication proceeds in __ direction(s) from a single Ori

94
Q

In replication of a circular bacterial chromosome, unwinding of DNA creates __ __ ahead of replication fork

A

supercoiled DNA

95
Q

In replication of a circular bacterial chromosome, DNA topoisomerases

A

relax supercoils by cutting the sugar phosphate backbone bond strands of DNA

96
Q

In replication of a circular bacterial chromosome, unwound broken strands are sealed by

97
Q

In replication of a circular bacterial chromosome, synthesis continues bidirectionally until

A

replication forks meet

98
Q

What do telomeres do?

A

protect the ends of eukaryotic chromosomes that require special mechanisms for replication because DNA polymerase can’t replicate some of the sequences at the 5’ end of DNA

99
Q

Telomeres consist of __ and don’t contain __

A

specific repetitive sequences; genes

100
Q

Telomeres are species-specific sequences and in humans that sequence us

101
Q

Telomeres prevent __ and maintain __

A

chromosome fusions; integrity of chromosomal ends

102
Q

Cells must preserve telomeres to maintain

A

normal genetic complement

103
Q

Telomerase RNA is complementary to

A

telomere repeat sequences

104
Q

Telomerase RNA serves as template for

A

addition of new DNA repeat sequences of telomere

105
Q

Additional rounds of telomere elongation occur after telomeres

A

translocate to newly-synthesized end

106
Q

After telomere extension, new RNA primer is synthesized and DNA is able to

A

be synthesized in 5’-3’ direction at 3’ end of template

107
Q

Most somatic cells have low expression of telomerase. Why?

A
  • telomeres shorten slightly at each cell division

- senescence after <50 generations in culture

108
Q

Germ cells, stem cells, and tumor cells have high expression of telomerase. Why?

A

at each generation, telomere length is maintained

109
Q

What do initiator proteins do?

A

bind to and open up origin of replication

110
Q

What does DNA polymerase III do?

A

catalyzes polymerization of new strands of complementary DNA

111
Q

What does DNA polymerase I do?

A

fills in gaps between Okazaki segments

112
Q

What does DNA helicase do?

A

unwinds double helix

113
Q

What do single-stranded binding proteins do?

A

keep helix open

114
Q

What does primase do?

A

creates RNA primers to initiate synthesis

115
Q

What does ligase do?

A

welds together Okazaki fragments

116
Q

What does topoisomerase do?

A

relaxes supercoils by nicking strands

117
Q

What does telomerase do?

A

extends telomeres

118
Q

What are 3 ways to ensure fidelity of DNA info?

A
  1. REDUNDANCY: either strand of the double helix can specify the sequence of the other strand
  2. PRECISION of cellular replication machinery: DNA polymerase I and III have proofreading ability
  3. DNA repair enzymes
119
Q

What are mutations?

A

heritable changes in DNA base sequences

120
Q

Mutations can be caused by

A

errors in DNA replication or environmental factors

121
Q

What is a forward mutation?

A

mutation that changes wild-type allele to a different allele
ex: A+ –> a or b+ –> B

122
Q

What is a reverse mutation (reversion)?

A

mutation that changes a mutant allele back into wild type

ex: a –> A+ or B –> b+

123
Q

Forward mutation rate is usually __ than reversion rate

124
Q

What is a substitution?

A

replacement of a base by another base

125
Q

What is a transition?

A

purine replaced by another purine, or pyrimidine replaced by another pyrimidine

126
Q

What is a transversion?

A

purine replaces by a pyrimidine, or pyrimidine replaced by a purine

127
Q

What are deletions?

A

when a block of 1 or more base pairs are lost from DNA

128
Q

What are insertions?

A

when a block of 1 or more base pairs are added to DNA

129
Q

What is an inversion?

A

180 degree rotation of a segment of DNA

130
Q

What happens in reciprocal translocation?

A

parts of two non homologous chromosomes change places

131
Q

Mutation rates are <10^-9 to >10^-3 per gene per

132
Q

Average mutation rate in gamete-producing eukaryotes is __ than that of prokaryotes

133
Q

Germ line mutations occur in __ and are __

A

gametes or in gamete precursor cells; transmitted to next generation

134
Q

Somatic mutations occur in __ and are __

A

non-germ cells; not transmitted to next generation of individuals, but are heritable across generations of cell-division

135
Q

Germ line mutations provide

A

raw material for natural selection

136
Q

Somatic mutations can affect __ and can lead to __

A

survival of an individual; cancer

137
Q

Base changes are often corrected by

A

DNA repair

138
Q

Incorporation of incorrect bases by DNA polymerase is rare because mispaired bases are recognized and excised by __ portion of DNA polymerase

A

3’ to 5’ exonuclease

139
Q

Complementation testing reveals

A

whether two mutations are in a single gene or in different genes

140
Q

Complementation testing can only be used with __ phenotypes

141
Q

A complementation group is a group of mutations that __ complement each other

142
Q

Proteins are chains of amino acids linked by

A

peptide bonds

143
Q

Polypeptides have an __ and a __

A

N terminus; C terminus

144
Q

Types of amino acids determine protein

A

shape, interactions, and function

145
Q

Primary structure of a polypeptide is the

A

amino acid sequence

146
Q

Secondary structure of a polypeptide is the

A

characteristic geometry of localized regions

147
Q

The tertiary structure of a polypeptide is the

A

complete 3D arrangement of a polypeptide (natural folding of polypeptide under normal conditions)

148
Q

The quaternary structure of a polypeptide are the

A

complexes of polypeptide subunits

149
Q

Mutations alter __, which can alter __, and thus modify __

A

nucleotide sequence; amino acid sequence; protein structure and function

150
Q

Protein recognition of DNA

A
  1. particular structure
  2. specific DNA shapes
  3. specific nucleotide sequences
151
Q

RNA polymerase transcribes DNA to

A

produce an RNA transcript

152
Q

Ribosomes translate mRNA sequences to

A

synthesize polypeptides

153
Q

What is the central dogma?

A

DNA –> RNA –> protein

154
Q

__ is the key to the transfer of info from DNA to RNA and from RNA to protein

A

pairing of complementary bases

155
Q

Polarities of DNA, RNA, and polypeptides help guide the

A

mechanisms of gene expressions

156
Q

Gene expressions requires __ and __

A

input of energy; participation of specific proteins and macromolecular assemblies

157
Q

Template strand of DNA is complementary to __ and to the __

A

mRNA; RNA-like strand of DNA

158
Q

5’ to 3’ in the mRNA corresponds to __ in the polypeptide

A

N-to-C terminus

159
Q

What are the 3 major chemical differences between RNA and DNA?

A
  • ribose sugar instead of deoxyribose
  • U instead of T
  • most RNAs are single stranded
160
Q

Transcription generates a __ using DNA as a template

A

5’-to-3’ polarity RNA chain

161
Q

RNA polymerase catalyzes

A

transcription

162
Q

Promoters are DNA sequences that

A

provide the signal to RNA polymerase for starting transcription

163
Q

Terminators are RNA sequences that

A

provide the signal to RNA polymerase for stopping transcription

164
Q

What are the 3 steps of RNA transcription?

A

initiation, elongation, termination

165
Q

What happens during initiation of transcription in RNA?

A
  • RNA polymerase binds to promoter sequence located near beginning of gene
  • sigma factor binds to RNA polymerase (reduces affinity of RNA polymerase for binding DNA, but inc. affinity for tight binding to promoter region)
  • region of DNA is unwound to form open promoter complex
  • phosphodiester bonds formed between first two nucleotides
166
Q

What happens during elongation of transcription in RNA?

A
  • sigma factor separates from RNA polymerase (–> core enzyme)
  • core RNA polymerase loses affinity for promoter and then moves in 3’-to-5’ direction on template strand
  • within transcription bubble, NTPs added to 3’ end of nascent mRNA
167
Q

What are the two kinds of terminators in bacteria?

A
  • extrinsic: require rho factor

- intrinsic: don’t require additional factors

168
Q

Terminators usually form

A

hairpin loops

169
Q

The sense strand of RNA has the same sequence as the

170
Q

The antisense strand of RNA is used as

A

the template for transcription

171
Q

Most promoters are __ to the transcription start point

172
Q

RNA splicing removes

173
Q

What are exons?

A

sequences found in a gene’s DNA and mature mRNA (Expressed regions)

174
Q

What are introns?

A

sequences found in DNA but not in mRNA (intervening regions) (INTrons INTerrupt the exons)

175
Q

RNA processing splices out __ and joins adjacent __

A

introns; exons

176
Q

Splicing is catalyzed by the

A

spliceosome

177
Q

Alternative splicing can produce

A

two different mRNAs from the same gene

178
Q

What are the 3 stop codons?

A

UGA, UAA, UAG

179
Q

Genetic code has __ codons

180
Q

T or F? Codons are nonoverlapping

181
Q

T or F? Genetic code is degenerate

182
Q

Reading frame is established from a fixed starting point

A

codon for translation initiation is AUG

183
Q

mRNAs and polypeptides have corresponding

A

polarities

184
Q

What are the 3 ways that mutations can be created?

A

frameshift, missense, and nonsense

185
Q

Codons must contain __ nucleotide

186
Q

Each point mutation affects only one

A

amino acid

187
Q

What is the start codon?

188
Q

What are missense mutations?

A

mutations that replace one amino acid with another

189
Q

What are conservative missense mutations?

A

missesnse mutation in which the chemical properties of mutant amino acid are similar to the original amino acid

190
Q

What are nonconservative missense mutations?

A

missense mutations in which the chemical properties of the mutant amino acid are different from original amino acid

191
Q

What are nonsense mutations?

A

mutations that change a codon that encodes an amino acid into a stop codon

192
Q

Frameshift mutations result from

A

insertion of deletion of nucleotides with the coding regions (no frameshift if multiples of three are inserted or deleted in frame)

193
Q

Silent mutations

A

do not alter the amino acid sequence

194
Q

Frameshift mutations alter the reading frame of codons AFTER

A

the point of insertion or deletion

195
Q

Ribosomes are the sites of

A

polypeptide synthesis

196
Q

How do ribosomes facilitate polypeptide synthesis?

A
  • recognizing mRNA features signaling start of translation
  • ensure accurate interpretation of code by stabilizing interaction between tRNA and mRNA
  • supply enzymatic activity to link aa’s
  • move 5’-to-3’ along mRNA molecule, exposing mRNA molecule, exposing mRNA molecules in sequence and ensure linear addition of aa’s
  • help terminate polypeptide synthesis by dissociating mRNA and the polypeptide
197
Q

During the initiation stage of translation in RNA,

A

start codon is AUG at 5’ end of mRNA

198
Q

During the elongation stage of translation in RNA,

A

amino acids are added to growing polypeptide

199
Q

During the termination stage of translation in RNA,

A

polypeptide synthesis stops at the 3’ end of the reading frame

200
Q

Small subunit of a ribosome

A

binds to mRNA

201
Q

Large subunit of a ribosome has __ activity

A

peptide transferase

202
Q

What are the 3 tRNA binding areas of a ribosome?

A

A, P, and E sites

203
Q

In prokaryotes, the ribosome binding site consists of a

A

Shine-Dalgarno sequence (AGGAGG in 5’ UTR before first AUG)

204
Q

The 3 sequential steps of the initiation phase in PROKARYOTES are

A
  1. small ribosomal subunit binds
  2. fMet-tRNA (3’ UAC 5’ anticodon) position in P site
  3. large subunit binds
205
Q

The initiation phase in EUKARYOTES consists of

A
  • small ribosomal subunit binds to 5’ cap (no S-D sequence), then scans the mRNA for the first AUG codon
  • initiator tRNA carries Met (not fMet)
206
Q

What happens during the elongation phase of translation of mRNAs on ribosomes?

A
  • ribosome moves along mRNA in 5’ to 3’ direction
  • addition of amino acids to C-terminus of polypeptide
  • charged tRNAs ushered into A site by elongation factors
207
Q

Polyribosomes consist of several ribosomes

A

translating the same mRNA

208
Q

What happens during the termination phase of translation of mRNAs on ribosomes?

A
  • no normal tRNAs carry anticodons for the stop codons
  • release factors bind to the stop codons
  • release of ribosomal subunits, mRNA, and polypeptide
209
Q

Loss of function mutations result in

A

reduced or abolished protein activity

210
Q

Loss of function mutations are usually

211
Q

Null (amorphic) mutations

A

completely block function of a gene product

212
Q

In hypomoprhic mutations,

A

gene product has weak, but detectable, activity

213
Q

Gain of function mutations

A

enhance a function or confer a new activity

214
Q

Gain of function mutations are usually

215
Q

Hypermorphic mutations

A

generate more gene product or the same amount of a more efficient gene product

216
Q

Neomorphic mutations

A

generate gene product with new function or that is expressed at inappropriate time or place

Genetics BSC-315 (3 decks)

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