Exam 2 Flashcards
(216 cards)
1
Q
The further apart two genes are, the greater the probability of
A
recombination
2
Q
What are synthetic genes?
A
genes located on the same chromosome
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
4
Q
__ __ leads to separation of linked genes
A
crossing over
5
Q
Departure from 1:1:1:1 ratio of F1 gametes in dihybrid cross indicates
A
linkage
6
Q
__ __ always most numerous or equal to recombinant
A
parental classes
7
Q
__ __ are never >50% of total F2 progeny
A
recombinant classes
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
9
Q
Recombinant gametes are __ __ than parental gametes when genes are linked
A
less frequent
10
Q
What is recombination?
A
the reciprocal exchange as a result of crossing-over during meiosis
11
Q
What is terminalization?
A
movement of chiamata
12
Q
What happens during anaphase?
A
chromosome separation occurs after chiasmata reach the telomeres
13
Q
What are the products of anaphase?
A
two recombinant and two parental gametes
14
Q
Dihybrid test cross of independently assorting genes produces a ___ progeny ratio
A
1:1:1:1
15
Q
Dihybrid test cross of completely linked genes produces a __ progeny ratio
A
1:1
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
17
Q
1 percent recombination =
A
1 RF (recombination frequency) = 1 map unit (m.u.) = 1 centiMorgan (cM)
18
Q
In linked genes, parents __ recombinants
A
>
19
Q
In unlinked genes (exhibit independent assortment), parents __ recombinants
A
=
20
Q
Linked genes must be __ and __ so that they do not assort independently
A
syntenic; sufficiently close together or on the same chromosome
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
22
Q
We can use recombination frequencies from __ for pairs of genes to establish relative gene position
A
two-point crosses
23
Q
Genes chained together by linkage relationships form a
A
linkage group
24
Q
Linkage group =
A
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
