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Flashcards in Exam 2 Deck (216):
1

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

recombination

2

What are synthetic genes?

genes located on the same chromosome

3

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

parental phenotypes

4

__ __ leads to separation of linked genes

crossing over

5

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

linkage

6

__ __ always most numerous or equal to recombinant

parental classes

7

__ __ are never >50% of total F2 progeny

recombinant classes

8

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

equivalent parental and recombinant phenotype ratios

9

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

less frequent

10

What is recombination?

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

11

What is terminalization?

movement of chiamata

12

What happens during anaphase?

chromosome separation occurs after chiasmata reach the telomeres

13

What are the products of anaphase?

two recombinant and two parental gametes

14

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

1:1:1:1

15

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

1:1

16

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

intermediate progeny ratios

17

1 percent recombination =

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

18

In linked genes, parents __ recombinants

>

19

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

=

20

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

syntenic; sufficiently close together or on the same chromosome

21

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

different chromosomes; sufficiently far apart on the same chromosome

22

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

two-point crosses

23

Genes chained together by linkage relationships form a

linkage group

24

Linkage group =

chromosome = 1 DNA molecule

25

Order of genes revealed by genetic mapping corresponds to

the actual order of genes along the chromosome

26

Recombination frequency becomes a less precise estimator of genetic distance at

large physical distances

27

What limits the correspondence between map and physical distance?

-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)

28

Genes close together on the same chromosome are __ and __

linked; do not assort independently, they segregate together

29

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

larger

30

The mechanism of recombination is

crossing over

31

__ are the visible signs of crossing over

chiasmata

32

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

greater

33

Recombination frequencies reflect

physical distance between genes

34

Recombination frequencies between two genes vary from

0% to 50%

35

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

chance events or linkage

36

Chi squared tests evaluate

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

37

What does the null hypothesis state?

observed values are no different from expected values

38

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

little deviation from expected; significant deviation from expected

39

Can a chi-square test prove linkage?

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

40

All of the genetics functions of DNA depend on

specialized proteins that "read" the info in DNA sequence

41

DNA is localized almost exclusively within

chromosomes

42

DNA contains four kinds of __ linked in a long chain

nucleotides

43

What are phosphodiester bonds?

covalent bonds joining adjacent nucleotides

44

What is a polymer?

linked chain of subunits

45

DNA is made of only __ different subunits

4

46

Protein is made of __ different subunits

20

47

DNA is a __ structure with __ diameter

helical; 20 A

48

Spacing between repeating units in DNA is

3.4 A

49

The DNA helix undergoes a complete turn every

34 S

50

What are the 4 nitrogenous bases of DNA

adenine, guanine, cytosine, thymine

51

What are the ratios of nitrogenous bases?

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

52

What are DNA's chemical constituents?

deoxyribose, phosphate, 4 nitrogenous bases

53

What are the purines?

adenine and guanine

54

What are the pyrimidines?

thymine and cytosine

55

The attachment of base to a sugar makes a

nucleoside

56

The addition of phosphate to a nucleoside makes a

nucleotide

57

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

5'-3'

58

Phosphodiester bonds always form covalent link between

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

59

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

hydrogen

60

Each base pair has the same

shape (can fit together without disrupting shape of chain)

61

The strands of DNA are

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

62

In a double helix of DNA, sugar phosphate backbones are

on the outside

63

In a double helix of DNA, base pairs are

in the middle

64

The double helix of DNA is two chains held together by

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

65

How does DNA carry information?

base sequence of A,T,C, and G's

66

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

DNA replication

67

What mechanisms allow genetic information to change?

-recombination
-mutations

68

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

gene functions

69

Most genetic info is "read" from

unwound DNA
e.g. synthesis of DNA or RNA

70

Some genetic info is accessible within

double-stranded DNA
e.g. DNA- binding proteins that regulate gene expression can access chemical info from "grooves" of DNA helix

71

What are the 3 possible models of DNA replication?

-semiconservative (Watson-Crick model)
-conservative
-dispersive

72

What is the conservative model of DNA replication?

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

73

What is the dispersive model of DNA replication?

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

74

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

-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

75

Energy for DNA synthesis comes from

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

76

__ __ catalyzes new phosphodiester bonds

DNA polymerase

77

What happens during initiation of DNA replication?

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

78

What happens during elongation of DNA replication?

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

79

What are the 3 strict requirements for DNA polymerase action?

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

80

DNA synthesis ALWAYS proceeds in the __ direction

5' to 3'

81

Template and newly synthesized strands are

antiparallel

82

Initiation begins at the

origin (Ori) of replication

83

What happens in the process of initiation?

-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

84

What happens in the process of elongation in DNA replication?

-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)

85

Leading strand of DNA synthesis has __ synthesis

continuous

86

Lagging strand of DNA synthesis has __ synthesis

discontinuous

87

What is an Okazaki fragment?

short DNA fragment on lagging strand

88

DNA polymerase moves along the template in the __ direction

3'-5'

89

What does DNA polymerase I do?

replaces RNA primer with DNA sequence

90

What does DNA ligase do?

covalently joins successive Okazaki fragments together

91

There are __ replication forks for each origin of replication

2

92

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

linear, circular; double, single

93

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

2

94

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

supercoiled DNA

95

In replication of a circular bacterial chromosome, DNA topoisomerases

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

96

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

ligase

97

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

replication forks meet

98

What do telomeres do?

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

Telomeres consist of __ and don't contain __

specific repetitive sequences; genes

100

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

TTAGGG

101

Telomeres prevent __ and maintain __

chromosome fusions; integrity of chromosomal ends

102

Cells must preserve telomeres to maintain

normal genetic complement

103

Telomerase RNA is complementary to

telomere repeat sequences

104

Telomerase RNA serves as template for

addition of new DNA repeat sequences of telomere

105

Additional rounds of telomere elongation occur after telomeres

translocate to newly-synthesized end

106

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

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

107

Most somatic cells have low expression of telomerase. Why?

-telomeres shorten slightly at each cell division
-senescence after <50 generations in culture

108

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

at each generation, telomere length is maintained

109

What do initiator proteins do?

bind to and open up origin of replication

110

What does DNA polymerase III do?

catalyzes polymerization of new strands of complementary DNA

111

What does DNA polymerase I do?

fills in gaps between Okazaki segments

112

What does DNA helicase do?

unwinds double helix

113

What do single-stranded binding proteins do?

keep helix open

114

What does primase do?

creates RNA primers to initiate synthesis

115

What does ligase do?

welds together Okazaki fragments

116

What does topoisomerase do?

relaxes supercoils by nicking strands

117

What does telomerase do?

extends telomeres

118

What are 3 ways to ensure fidelity of DNA info?

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

What are mutations?

heritable changes in DNA base sequences

120

Mutations can be caused by

errors in DNA replication or environmental factors

121

What is a forward mutation?

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

122

What is a reverse mutation (reversion)?

mutation that changes a mutant allele back into wild type
ex: a --> A+ or B --> b+

123

Forward mutation rate is usually __ than reversion rate

greater

124

What is a substitution?

replacement of a base by another base

125

What is a transition?

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

126

What is a transversion?

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

127

What are deletions?

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

128

What are insertions?

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

129

What is an inversion?

180 degree rotation of a segment of DNA

130

What happens in reciprocal translocation?

parts of two non homologous chromosomes change places

131

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

gamete

132

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

higher

133

Germ line mutations occur in __ and are __

gametes or in gamete precursor cells; transmitted to next generation

134

Somatic mutations occur in __ and are __

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

135

Germ line mutations provide

raw material for natural selection

136

Somatic mutations can affect __ and can lead to __

survival of an individual; cancer

137

Base changes are often corrected by

DNA repair

138

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

3' to 5' exonuclease

139

Complementation testing reveals

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

140

Complementation testing can only be used with __ phenotypes

recessive

141

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

DO NOT

142

Proteins are chains of amino acids linked by

peptide bonds

143

Polypeptides have an __ and a __

N terminus; C terminus

144

Types of amino acids determine protein

shape, interactions, and function

145

Primary structure of a polypeptide is the

amino acid sequence

146

Secondary structure of a polypeptide is the

characteristic geometry of localized regions

147

The tertiary structure of a polypeptide is the

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

148

The quaternary structure of a polypeptide are the

complexes of polypeptide subunits

149

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

nucleotide sequence; amino acid sequence; protein structure and function

150

Protein recognition of DNA

1. particular structure
2. specific DNA shapes
3. specific nucleotide sequences

151

RNA polymerase transcribes DNA to

produce an RNA transcript

152

Ribosomes translate mRNA sequences to

synthesize polypeptides

153

What is the central dogma?

DNA --> RNA --> protein

154

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

pairing of complementary bases

155

Polarities of DNA, RNA, and polypeptides help guide the

mechanisms of gene expressions

156

Gene expressions requires __ and __

input of energy; participation of specific proteins and macromolecular assemblies

157

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

mRNA; RNA-like strand of DNA

158

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

N-to-C terminus

159

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

-ribose sugar instead of deoxyribose
-U instead of T
-most RNAs are single stranded

160

Transcription generates a __ using DNA as a template

5'-to-3' polarity RNA chain

161

RNA polymerase catalyzes

transcription

162

Promoters are DNA sequences that

provide the signal to RNA polymerase for starting transcription

163

Terminators are RNA sequences that

provide the signal to RNA polymerase for stopping transcription

164

What are the 3 steps of RNA transcription?

initiation, elongation, termination

165

What happens during initiation of transcription in RNA?

-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

What happens during elongation of transcription in RNA?

-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

What are the two kinds of terminators in bacteria?

-extrinsic: require rho factor
-intrinsic: don't require additional factors

168

Terminators usually form

hairpin loops

169

The sense strand of RNA has the same sequence as the

mRNA

170

The antisense strand of RNA is used as

the template for transcription

171

Most promoters are __ to the transcription start point

upstream

172

RNA splicing removes

introns

173

What are exons?

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

174

What are introns?

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

175

RNA processing splices out __ and joins adjacent __

introns; exons

176

Splicing is catalyzed by the

spliceosome

177

Alternative splicing can produce

two different mRNAs from the same gene

178

What are the 3 stop codons?

UGA, UAA, UAG

179

Genetic code has __ codons

triplet

180

T or F? Codons are nonoverlapping

T

181

T or F? Genetic code is degenerate

T

182

Reading frame is established from a fixed starting point

codon for translation initiation is AUG

183

mRNAs and polypeptides have corresponding

polarities

184

What are the 3 ways that mutations can be created?

frameshift, missense, and nonsense

185

Codons must contain __ nucleotide

>1

186

Each point mutation affects only one

amino acid

187

What is the start codon?

AUG

188

What are missense mutations?

mutations that replace one amino acid with another

189

What are conservative missense mutations?

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

190

What are nonconservative missense mutations?

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

191

What are nonsense mutations?

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

192

Frameshift mutations result from

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

193

Silent mutations

do not alter the amino acid sequence

194

Frameshift mutations alter the reading frame of codons AFTER

the point of insertion or deletion

195

Ribosomes are the sites of

polypeptide synthesis

196

How do ribosomes facilitate polypeptide synthesis?

-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

During the initiation stage of translation in RNA,

start codon is AUG at 5' end of mRNA

198

During the elongation stage of translation in RNA,

amino acids are added to growing polypeptide

199

During the termination stage of translation in RNA,

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

200

Small subunit of a ribosome

binds to mRNA

201

Large subunit of a ribosome has __ activity

peptide transferase

202

What are the 3 tRNA binding areas of a ribosome?

A, P, and E sites

203

In prokaryotes, the ribosome binding site consists of a

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

204

The 3 sequential steps of the initiation phase in PROKARYOTES are

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

205

The initiation phase in EUKARYOTES consists of

-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

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

-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

Polyribosomes consist of several ribosomes

translating the same mRNA

208

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

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

209

Loss of function mutations result in

reduced or abolished protein activity

210

Loss of function mutations are usually

recessive

211

Null (amorphic) mutations

completely block function of a gene product

212

In hypomoprhic mutations,

gene product has weak, but detectable, activity

213

Gain of function mutations

enhance a function or confer a new activity

214

Gain of function mutations are usually

dominant

215

Hypermorphic mutations

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

216

Neomorphic mutations

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