Pre Midterm Notes Flashcards
1
Q
what is it called when you cut just one strand of DNA?
A
a nick
2
Q
how does DNA become super coiled
A
single strand nick
multiple 360 rotation
ligation
3
Q
what is it called when you seal the nick?
A
ligation
4
Q
how much bigger is a eukaryote than a prokaryote?
A
10x
5
Q
what is supercoiling?
A
a double helix (as of DNA) that has undergone additional twisting in the same direction as or in the opposite direction from the turns in the original heli
6
Q
how large is the human nucleus?
A
5-10 micrometers
7
Q
what is a eukaryotic chromosome composed of?
A
- one large linear molecule of DNA
- 5 histones (positive charged)
- divergent group of non-histone proteins
8
Q
DNA + histone + protein =
A
chromatin
9
Q
how many levels of DNA packaging are in chromatin
A
3:
- nucleosome
- 30 nm chromatin fiber
- inter-phase chromosome
10
Q
level 1 : nucleosomes
A
- 146 nucleotide pairs of DnA wrapped as 1 3/4 turns around an octamer histone
- linker DNA carry in length from 8-114 nucleotide pair
- width: 11 nm
11
Q
Nucleosome core
A
-consist of 2 molecules of each of the 4 histones 2(H2a + H2b + H3 + H4)
12
Q
what does H1 do
A
- comes in and seals the 1 3/4 turn
- just one
- becomes complete nucleosome once H1 is involved
13
Q
level 2: 30 nm chromatin fibre
A
- have chromatin DNA and protein
- least elegant step
- compact everything into a fibre that ends up being 30 nm wide
- linear
14
Q
level 3: inter-phase chromosome
A
- divergent non-histone proteins
- fibre forms loops (less space)
- 300 nm wide
- tethered to scaffold
15
Q
what is inter-phase chromosome?
A
how your DNA in your cells look when they’re not dividing
16
Q
what is simplest level of DNA?
A
double stranded helical structure
17
Q
what does interphase chromosome wrap around to become metaphase chromosome?
A
chromosome scaffold
18
Q
what is another level of packaging that a chromosome undergoes during mitosis?
A
the metaphase chromosome
19
Q
what kind of DNA does each eukaryotic chromosome contain?
A
nucleosomes
20
Q
what is a nucleosome?
A
1 giant molecule of DNA packaged into 11 nm ellipsoidal beads
21
Q
what is a gene?
A
a genetic factor that helps determine a characteristic
22
Q
what is an allele?
A
One of two or more alternative forms of a gene
23
Q
how is genetic info carried?
A
DNA
24
Q
where are genes located?
A
chromosomes
25
what is the flow of genetic info transfer?
DNA to RNA to protein
26
what is a locus?
Specific place on a chromosome occupied by an allele
27
what is a genotype?
Set of alleles possessed by an individual organism
28
what is a heterozygote?
An individual organism possessing two different alleles at a locus
29
what is a homozygote
An individual organism possessing two of the same alleles at a locus
30
what is a phenotype?
The appearance or manifestation of a character
31
what did Gregor Johann Mendel discover?
the basic principles of heredity
32
what is the phenotypic ratio in the F2 generation of a monohybrid cross?
3:1
33
what is the phenotypic ratio in the F2 generation of a dihybrid crop?
9:3:3:1
34
what do we assume if the trait is rare and autosomal recessive?
individuals who marry into the pedigree are not carriers: homozygous for the normal allele
35
what are the 2 types of recessive mutations?
null/amorphic alleles
| hylomorphic alleles
36
what is a Null/Amorphic allele?
a nonfunctional protein is produced
or
no protein is produced
37
what is a hylomorphic allele?
a poorly functioning protein is produced
or
reducing amounts of a normally function protein is produced
38
when do you use the multiplication rule?
when the word AND is used
39
when do you use the addition rule?
when the word OR is used
40
what often involves a loss of gene function?
recessive mutations
41
what are the 2 types of dominant mutations?
dominant hypermorphic alleles
or
neomorphic alleles
42
what often involves gain/change of gene function?
dominant mutations
43
what is a dominant hypermorphic alleles?
- Negative phenotypic consequences due to the over-production of a normal protein
OR
- Negative phenotypic consequences due to the production of a protein with increased activity levels
44
what is a neomorphic allele?
- Negative phenotypic consequences due to the presence of an altered protein that has a new function
- Negative phenotypic consequences when the altered protein interferes with the wildtype protein (Dominant-negative allele
45
why for traits that are rare and dominant, affected individuals are most likely to be heterozygous (Bb)?
If the trait is rare in the population, then matings between Bb individuals would be infrequet
46
what is incomplete dominance?
Bb is intermediate between homozygous phenotype
47
what is codominance?
Bb exhibits phenotypes of both homozygote
48
true or false:
| Multiple Alleles Often Exist for a Gene at a Particular Locus
true
49
what does the IA allele in blood encode?
a transferase which adds acetylgalactosamine
50
what does the IB allele in blood encode?
a transferase which adds galactose
51
what does the i allele in blood encode?
a non-functional transferase
52
what does the IAIB blood type encode?
acetylgalactosamine and galactose
53
what is a wild type allele?
a functional enzyme or other protein is produced (most common found in a natural population)
54
what is a loss of function allele?
an enzyme or other protein is no longer being produced, is produced at lower levels, or is nonfunctional
55
what is haplosufficiency?
Half as much protein is synthesized yet this is often sufficient to achieve the wildtype phenotype
56
what's an example of a gain of function dominant allele?
Huntington's disease
57
what is haploinsufficent?
in the heterozygote, half as much protein is synthesized and this is not sufficient for a normal phenotype
58
when do you get a severe mutant phenotype?
recessive amorphic loss-of-function allele does not produce a functional polypeptide
OR
dominant-negative allele produces a polypeptide that interferes with the wild-type polypeptide
59
when do you get a mild mutant phenotype?
recessive hylomorphic loss-of-function allele produces a partially functional polypeptide
60
what is penetrance?
The proportion of individual organisms having a particular genotype that express the expected phenotype
-variation in the population
61
what is expressivity?
The degree to which a phenotype is expressed (mild to severe);
variation in the individual
62
what is polydactyly an example of?
incomplete penetrance
63
what are some examples of variable expressivity?
split hand-foot syndrome
piebaldism
Huntington's disease
64
what causes incomplete penetrance and expressivity?
due to the effects of other genes and to environmental factors that can alter or completely suppress the effect of a particular gene
65
what are the 4 environmental factors that can affect phenotypic expression?
1. age
2. sex
3. temperature
4. chemicals
66
what is the norm of reaction?
The range of phenotypes expressed by a single genotype under different environmental conditions
67
what is a phenocopy?
change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene
68
what is Mendel's law of independent assortment?
The inheritance pattern of one trait will not affect the inheritance pattern of another trait
69
when will complementation occur?
when two strains of an organism with different homozygous recessive mutations that produce the same phenotype, produce offspring of the wild-type phenotype when mated or crossed
70
true or false:
| complementation can occur if the mutations are in the same gene
false:
| only if they're in different genes
71
what is a heterogeneous trait?
a mutation in any one of a number of genes can give rise to the same phenotype
72
what is epistasis?
The masking of the expression of one gene by another.
| No new phenotypes are produced
73
what is the F2 phenotypic ratio of the recessive epistasis?
9:3:4
74
what is the F2 phenotypic ratio of the dominant epistasis?
12:3:1
75
what is the F2 phenotypic ratio of the recessive lethal allele?
2:1
76
what is the F2 phenotypic ratio of the incomplete dominance or codominance?
1:2:1
77
what is the F2 phenotypic ratio of complementation?
9:7
78
what is pleiotropy?
when A single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects
79
what is heterosis?
when 2 different inbred lines are crossed
80
what does inbreeding do?
increases the frequency of homozygotes and decreases the frequency of heterozygotes
81
what is the Hardy Weinberg principle?
predicting genotypes through allele frequencies in a population
82
what is the Hardy Weinberg equation?
p^2 + 2pq + q^2
83
what needs to be absent for the Hardy Weinberg Principle t be correct?
evolutionary influences:
1. Nonrandom mating
2. Unequal survival
3. Population subdivision
4. Migration
84
what is the expected frequency of heterozygotes in a population with allelic frequency x and y that is in Hardy–Weinberg equilibrium?
a. x+ y
b. xy
c. 2xy
d. (x-y)2
c. 2xy
85
what is dosage compensation?
a way of equalizing gene expression in the face of different gene dosa
86
what are the only 2 chromosomes that pair even though they're not homologous?
the X and Y
87
where are X and Y chromosomes homologous?
only at pseudoautosomal regions
88
what is a Barr body?
inactive X chromosome
89
how many active X chromosomes can a person have?
1
90
what are genetic mosaics?
females that are heterozygous for X-linked traits
91
what is polyploid?
more than 2 sets of chromosomes
92
how much of the plant kingdom is polyploidy?
30-35% of flowering plants
93
true or false:
| polyploidy is rare in the animal kingdom
true
94
describe autopolyploids
- the chromosome sets are all identical
| - All chromosomes are derived from the same species
95
what d autopolyploid plants usually have?
–More vegetative growth (larger cells, thicker leaves, bigger flowers, larger plants, bigger fruits)
–Less seed production
96
why are many polyploids sterile?
due to problems with pairing and separation of homologous chromosomes in meiosis
97
what are allopolyploids?
polyploids that are the result of the crosses between 2 or more species
98
describe polyploidy in animals
- interspecies crosses can result in a sterile animal
| - Chromosome doubling which potentially could restore fertility is not well tolerated
99
what is aneuploidy?
Diploid genome which lacks a chromosome or has an extra chromosome
100
what can cause aneuploidy?
Meiotic nondisjunction
101
what are the only 3 autosomal trisomies seen as live births in humans?
- trisomy 21 (Down syndrome)
- trisomy 13 (Patau syndrome)
- trisomy 18 (Edwards syndrome)
102
what are the aneuploid conditions involving sex chromosomes?
- X0 Turner Syndrome
- XXY Klinefelter Syndrome
- XXX Triple X Syndrome
- XYY Double Y male
103
what is another word for bivalent?
homologous pair
104
a diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species?
2n + 1 = 36 + 1 = 37
105
what is the cause of Down's syndrome?
96% meiotic non-disjunction
| 4% Robertsonian translocation of the chromosome 21 long arm onto the long arm of chromosome 14
106
Why Is There A Correlation Between The Incidence Of Trisomies And Maternal Age?
Bivalents with crossovers near the ends of the chromosomes are fragile and are increasingly unstable over time
107
in humans, where do germ cells remain until ovulation?
arrested prophase 1
108
what sorts of chemicals can cause nondisjunction?
```
colchicine
Bisphenol A (BPA)
```
109
what is deletion?
a missing chromosome segment
110
what is duplication?
an extra chromosome segment
111
what is paracentric inversion?
not including the centromere in the inversion
112
what is pericentric inversion?
including the centromere in the inversion
113
when does translocation occur?
when a segment from one chromosome is detached and reattached to a different (nonhomologous) chromosome
114
what is reciprocal translocations?
pieces of two nonhomologous chromosomes are exchanged without any net loss of genetic material
115
how are compound chromosomes formed?
by the fusion of homologous chromosomes, sister chromatids, or homologous chromosome segments
116
how are Robertsonian translocations formed?
by the fusion of two nonhomologous chromosomes at their centromeres
117
true or false:
| genes that are of the same chromosome travel through meiosis together
true
118
what did TH Morgan discover?
- Genes are “linked” if present on the same chromosome
| - The divergence from linkage is called recombination
119
what did AH Sturtevant discover?
The frequency of recombination reflects distance between genes
120
map units =
recombinants / total x 100
121
if genes are linked, what do you see in F1?
two major classes of offspring with equal frequencies with two minor classes of offspring that are the result of recombinant gametes in the dihybrid parent
122
when does homologous recombination occur?
prophase 1 of meiosis
123
what is a chiasma?
- the physical junction between the homologous chromatid
| - site where recombination occur
124
true or false:
| multiple crossovers can be simultaneously taking place over the same tetrad
true
125
when does crossing over occur?
prophase of meiosis 1
126
true or false:
the closer genes are to each other on the chromosome, the likelier they are to crossover together, decreasing the likelihood of a recombinant gamete
true
127
what are the 3 possible scenarios for dihybrid cross AaBb X AaBb
1. Genes A and B are independently assorting (4 classes of offspring with a 9:3:3:1 ratio)
2. Genes A and B are tightly linked so that crossing over does not happen (2 classes of offspring with a 3:1 ratio)
3. Genes A and B are linked and crossing-over occurs (variations in the 3:1 ratio)
128
what is recombination caused by?
by a physical exchange between paired homologous chromosomes early in prophase of the first meiotic division after chromosomes have duplicated
129
true or false:
At any one point along a chromosome, the process of exchange (crossing over) involves only two of the four chromatids in a meiotic tetrad
true
130
when do crossovers become visible as chiasmata?
late in prophase 1
131
how can linkage between human genes be detected?
by analyzing pedigrees
132
true or false:
| pedigree analyses can have a limited success in complex genetic traits
true
133
what are the mechanisms of genetic exchange in bacteria?
conjugation
transformation
transduction
134
what makes bacteria a valuable research object?
- Small size
- Rapid reproduction
- Selective media (e.g., antibiotics) that can easily identify the presence of an active allele
- Simple structures and physiology
- Genetic variability
135
how do bacteriophages reproduce?
by infecting bacterial cells
136
what do bacteriophages produce on plates with dense bacterial cultures?
plaques
137
describe bacteriophage T4
- Protein head
- Genome contains 168,800 base pairs and 150 characterized genes
- This is a fairly large and complex genome
- The phage goes through a lytic phase
138
describe bacteriophage lambda
- Genome contains, 48,502 base pairs and about 50 genes
| - May be lytic or lysogenic
139
Conjugation between an F+ and F− cell usually results in which of the following?
a. Two F+ cells
b. Two F− cells
c. An F+ and an F− cell
d. An Hfr and an F+ cel
a. Two F+ cells
140
what is the bacterial genome?
circular molecules of several million base pairs, called bacterial chromosome
141
where does additional genetic material reside?
in plasmids (small circular DNA) that can replicate independently of the bacterial chromosome
142
what is an episome?
large circular DNA that can integrate into the bacterial chromosome for replication or remain separate
143
true or false:
| bacteria have meiosis
false
144
true or false:
| gene transfer in bacteria is unidirectional
true:
| from donor cell to recipient cell
145
how can gene mutations in bacteria be observed?
- Colony colour and morphology
- Nutritional mutants (can not metabolise certain sugars, like lactose or galactose)
- Prototrophs and auxotrophs (can not make certain amino acids, these need to be added to the growth medium)
- Antibiotic resistance
146
define transformation
transfer of a free (out of the cell) piece of DNA from one bacterium into another
147
define conjugation
direct transfer of DNA from one cell to another via the establishment of a cytoplasmic bridge
148
define transduction
transfer of genes from one cell to another via bacteriophage (vector)
149
which parasexual process in bacteria requires cell contact?
conjugation
150
which parasexual process in bacteria is sensitive to DNase?
transformation
151
true or false:
| Transformation can be used to determine the distance between bacterial gene
true
152
what is transformation measured as?
a change in phenotype that occurs with a certain frequency
153
what is the sexual reproduction in conjugation mediated by?
the Fertility or F factor
154
how does an F-factor exist?
as an extra-chromosomal DNA
OR
it can insert into the bacterial chromosome and replicate as part of it
155
true or false:
| in general plasmids are not required for the survival of the host cell
true:
| they serve as auxiliary genetic elements
156
what are the functions of the genetic material?
must replicate, control the growth and development of the organism, and allow the organism to adapt to changes in the environment
157
where is genetic info of most living things stored?
in DNA
158
where is genetic info present in some viruses?
RNA
159
how are nucleotides joined?
phosphodiester bonds
160
true or false:
| %A=%C
false:
%A=%T
%C=%G
161
true or false:
| A+G=T+C
true
162
which are the 2 purines?
A and G
163
which are the 2 pyrimidines
T and C
164
what did Erwin Chargaff determine?
the precise base composition of different types of DNA
165
what did William Astbury discover?
X-ray diffraction Analysis showed that DNA is a polymer of stacked bases
166
what did Rosalind Franklin & Maurice Wilkins discover?
DNA is a helix
167
what are the assumptions of the Watson and Crick model?
- DNA is a double helix
- The two strands were anti-parallel
- The sugars form a phosphate backbone
- The bases are held together by H bonds
168
true or false:
| DNA has antiparallel strands
true
169
true or false:
| The two strands of the helix have opposite chemical polarity (5’ and 3’ ends)
true
170
true or false:
| the U-tube experiment concluded that genetic exchange requires direct contact between bacterial cells
true
171
true or false:
| the rate of cotransformation is proportional to the distance between genes
false:
| inversely proportional
172
what is the transforming substance in the Avery–MacLeod–McCartyexperiment?
DNA
173
what is the genetic material of TMV?
RNA
