Molecular Biology and Genetics Flashcards
1
Q
What is a sex-linked chromosome?
A
Genes that appear on the sex chromosomes
2
Q
What are linked genes?
A
Two genes on the same chromosome
3
Q
What are some examples of sex-linked traits
A
Red/green colour blindness
Haemophilia
4
Q
Define autosomes
A
Chromosomes that are not sex chromosomes
5
Q
What is haploid/diploid sex determination?
A
When an individual with a haploid set of chromosomes is (for example) male and an individual with a diploids set of chromosomes is female
6
Q
How is sex determined in humans?
A
the presence of the Y chromosome ensures that an individual is male because it encodes the development of the testis
7
Q
How do you describe individuals which have two different sex chromosomes (such as males in humans or females in birds)
A
Heterogametic
8
Q
How do you describe individuals which have two of the same sex chromosomes (such as females in humans or males in birds)
A
Homogametic
9
Q
Define hemizygous
A
eg. a male is hemizygous
Males can not be homozygous or heterozygous because they only have one X chromosomes which means they cannot have two different alleles for the same trait
10
Q
If a trait is a sex-linked trait then it appear on the _______ chromosome
A
X
11
Q
X-linked DOMINANT alleles will show more in
A
females
12
Q
X-linked RECESSIVE alleles will show more in
A
males
13
Q
Explain the predicted phenotypes of the two sons and two daughters of parents if the
- mum is a normal homozygous female
- dad is a colour blind male
and colour blindness is a recessive sex-linked trait
A
- the mother can only produce eggs that have X chromosomes that are normal (eg. n,n)
- the father can produce sperm with either an X chromosome (that will be colour blind - c) and produce a girl, or a Y chromosome and produce a boy
- the daughters of this couple will have two X chromosomes, one from mum and one from dad so will both have the genotype XnXc and be carries
- the sons of this couple will carry the Y chromosome which means they can not inherit the c from their dad so must both have the genotype XnY and be normal
14
Q
Explain the predicted phenotypes of the two sons and two daughters of parents if the
- mum is a carrier female
- dad is a normal male
and colour blindness is a recessive sex-linked trait
A
- the mother can produce eggs that have X chromosomes are with normal (n) or colour blind (c)
- the father can produce sperm with either an X chromosome (that will be normal - n) and produce a girl or, a Y chromosome and produce a boy
- the sons of this couple will inherit the Y chromosome from the dad but can inherit the normal (n) X chromosome from mum or the colour blind (c) X chromosome from mum
- half the sons will have the genotype XnY and be normal and half will have the genotype XcY and be colour blind
- the daughters of this couple will inherit the Xc from their dad and either the Xc or Xn from their mum
- half the daughters will have the genotype XnXn and be normal and half the daughters will have the genotype XnXc and be carriers
15
Q
Linked genes show a bias towards
A
parental phenotypes
16
Q
Independent assortment creates new combinations of ________ genes
A
unlinked
17
Q
Crossing over creates new combinations of ________ genes
A
linked
18
Q
What does Mendel’s 1st Law (Law of Segregation) state?
A
Genes segregate at meiosis so that each gamete contains only 1 of the two possessed by the parent
19
Q
What does Mendel’s 2nd Law (Law of Independent Assortment) state?
A
Alleles of different genes assort independently during gamete formation
20
Q
Define a population
A
Localised groups of individuals of the same species
21
Q
Define the gene pool
A
total aggregate of genes (and their alleles) in the population at one time
22
Q
Why might we have to estimate the frequencies of genotypes in a population?
A
- to predict how many individuals in a population will inherit a genetic disease
- to estimate the proportion of individuals in a population who are carriers of a genetic disease
23
Q
p + q = ?
where p = ________ and q = ________
A
1
p = frequency of dominant alleles
q = frequency of recessive alleles
24
Q
What is the Hardy-Weinberg equation and when would it be used?
A
p² + 2pq + q² = 1
It would be used to predict the number of genotypes in a population
25
What do p², 2pq and q² represent in the Hardy-Weinberg equation?
- p² = the proportion of homozygous dominant genotypes there are in the population
- q² = the proportion of homozygous recessive genotypes there are in the population
- 2pq = the proportion of heterozygous dominant genotypes there are in the population
26
What are 7 ways allele frequencies can change?
1. non-random mating
2. random genetic drift
3. bottleneck effect
4. founder effect
5. natural selection
6. gene flow or migration
7. mutation
27
What are two types of non-random mating?
- assortative mating
| - inbreeding
28
Define assortative mating
Intentionally choosing mates that look identical to you or the complete opposite
29
Define inbreeding
Breeding between related individuals
30
Define random genetic drift
A random change in allele frequencies due to sampling error over generations
31
Define bottleneck
A random event causes a collapse of the population so that only a few individuals survive. This causes a change in allele frequency as some alleles become fixed and some become lost
32
Define the founder effect
A few individuals leave a population and establish new population in a new location, so there is reduced genetic diversity in new population
33
What are 5 types of natural selection?
1. stabilising selection
2. disruptive selection
3. directional selection
4. sexual selection
5. frequency dependent selection
34
Define stabilising selection and give an example
Extreme variations are selected against and middle range are retained in greater numbers. This reduces variation but does not change the mean.
eg. birth weight in babies
35
Define directional selection and give an example
When the adaptive phenotype is shifted in one direction and one phenotype is favoured over others. This changes the mean towards one extreme
eg. taller giraffes are favoured or wild mustard evolving to cabbage, cauliflower, Brussel sprouts, kale, broccoli
36
Define disruptive selection and give an example
Phenotypic extremes are favoured at the expense of intermediate phenotypes. This means two peaks form
eg. beak size in West African black bellied seed crackers
37
Define sexual selection and give an example
Females are more likely to mate with males with an attractive phenotype
eg. Females like males with long tails therefore long tailed males are more likely to mate so over time we have a population with longer tails
38
Define frequency dependent selection
Over a long period of time, natural selection maintains an equal proportion of differing phenotypes
eg. left or right mouthed Perissodus microlepis (one year there is a higher frequency of right mouthed individuals but then the fish they feed on stop them from feeding so the next year left mouthed individuals are more common and so on
39
Define a cline and give an example
The gradual geographic change in genetic/phenotypic composition
eg. more clovers producing cyanide in warmer climates
40
Describe how a mutation can act within a population
- Mutations occur randomly
- very slow to act
- usually disadvantageous
41
Define migration
an individual from another population successfully mates (and contributes) to the gene pool
42
What does migration do to a population?
- brings new alleles
- changes proportions of existing alleles
- changes population size
- makes two populations more similar
43
What is the role of primase?
It makes RNA primers in the 5` to 3` direction. The RNA primer is the starting point for DNA polymerisation and it provides the 3` OH group
44
What is the role of DNA polymerase |||?
It is the enzyme that synthesises a new DNA strand by adding complementary nucleotides to the parent strand. DNA polymerase ||| uses the 3` OH group from the RNA primer to start building DNA in the 5` to 3` direction
45
What is the role of helicase?
It is the enzyme that pulls strands of DNA apart at the origin of replication
46
Why does helicase pull DNA apart at the origin of replication?
Because the origin of replication is an A/T rich region which means that there are only two H bonds to break instead of three
47
What is the role of topoisomerase?
It cuts off the DNA and sticks it back together to remove the pressure from it being twisted so hard when helicase pulls the strands apart. The DNA is no longer twisted when it is put back together
48
What is the role of single stranded DNA binding proteins?
They stop the newly separated DNA from snapping back together.
The cells like to break down single stranded molecules so the SSBP protect the DNA from this happening
49
What is the role of DNA polymerase |?
It removes the RNA primer and will use the 3` OH groups from the Okazaki fragments next door to fill the gap between the neighbouring Okazaki fragment
50
What is the role of DNA ligase?
It makes a phosphodiester bond between the 5` phosphate group and the 3` OH group of neighbouring Okazaki fragments
51
Describe how leading strands are synthesised
1. helicase separates the strands of DNA
2. single stranded DNA binding proteins hold the strands apart and protect the strands
3. Primase builds a primer in the 5` to 3` direction
4. DNA polymerase ||| extends from the primer by adding nucleotides in the 5' to 3` direction
52
Describe how the lagging strand is synthesised
1. helicase separates the strands of DNA
2. single stranded DNA binding proteins hold the strands apart and protect the strands
3. Primase builds a primer in the 5` to 3` direction
4. DNA polymerase ||| extends from the primer by adding nucleotides in the 5' to 3` direction
5. DNA polymerase | removes the RNA primer and fills the gaps between the Okazaki fragments by building DNA nucleotides from the 3' OH group of the RNA polymer
6. DNA ligase makes a phosphodiester bond between the 5` phosphate group and the 3` OH group of neighbouring Okazaki fragments
53
When can DNA errors be corrected?
During replication or after replication
54
DNA errors are fixed during replication by
an exonuclease
55
DNA errors are fixed after replication by
an endonuclease
56
How does an exonuclease fix errors in DNA during replication?
DNA polymerase ||| acts as an exonuclease and removes the incorrect base from the 3` end and works towards the 5` end removing the incorrect base. DNA polymerase then adds the correct base
57
How does an endonuclease fix errors in DNA after replication?
- the endonuclease removes a chunk of bases including the incorrect one
- this takes a chunk out of the strand
- a DNA polymerase adds the correct bases
- DNA ligase forms the phosphodiester bonds between the new bases and the existing ones
58
What is PCR and why is it important?
Polymerase Chain reaction
| to amplify of a specific (target) region of DNA.
59
Which PCR components are the same as in vivo DNA replication?
DNA template
Primers
DNA polymerase
dNTPs
60
What is the role of the DNA template in PCR?
It is the DNA molecule to which complementary nucleotides can be matched to make identical copies via DNA synthesis
61
What is the role of the primers in PCR?
they provide a free 3` OH group to initiate DNA synthesis
62
What is the role of the DNA polymerase in PCR?
it is the enzyme which adds nucleotides complementary to the DNA template and joins them together forming the phosphodiester bond
63
What is the role of the dNTPs in PCR?
free nucleotide blocks (equal amounts of A, C, G and T) used by the DNA polymerase
64
What are the three steps of PCR?
Denaturation
Annealing
Extension
65
Describe the process of denaturation in PCR
The double stranded DNA is denatured (separated) by briefly heating the sample to 95°C.
66
Describe the process of annealing in PCR
the sample is cooled to allow annealing (joining) of the primers to the single strands of DNA. The annealing temperature depends on the primer sequence, but is generally between 45-70°C.
67
Describe the process of extension in PCR
the temperature is increased to 72°C and the DNA polymerase makes the new DNA strand, starting at the primers and adding new nucleotides to match the existing strand in the 5’ to 3’ direction
68
What is the consequence of errors in DNA replication not being fixed?
The DNA error becomes part of the template, there is a permanent DNA change and mutation
69
What is a karyotype?
An ordered, visual representation of chromosomes in a cell
70
What is a locus?
a place or location on a chromosomes where we find a gene
71
What are the phases of the cell cycle?
Interphase
| Mitotic phase
72
What occurs during interphase?
G1
S phase
G2
73
What happens during S phase?
DNA replication
74
What occurs during the mitotic phase?
Mitosis and cytokinesis
75
What is mitosis?
A type of cell division that produces two genetically identical daughter cells
76
What are the 5 stages of mitosis?
```
prophase
prometaphase
metaphase
anaphase
telophase
```
77
Describe what happens during prophase
- the chromosomes have condensed and become visible
| - centrosomes form early mitotic spindles and move towards each cell pole
78
Describe what happens during prometaphase
- the nuclear envelope fragments
- the kinetochore microtubules connect to the kinetochores
- the centrosomes have moved to each pole of the cell
79
Describe what happens during metaphase
- the pairs of sister chromatids line up along the metaphase plate
80
Describe what happens during anaphase
- the kinetochore microtubules shorten pulling the sister chromatids apart
- the non-kinetochore microtubules lengthen to start to push the ends of the cells apart
81
Describe what happens during telophase/cytokinesis
- separate nuclei begin to form
| - the cells separate
82
What is the sexual life cycle?
- meiosis to form egg and sperm
- fertilisation to form diploid gametes
- mitosis and development
- make gametes via meiosis
83
What is the purpose of meiosis?
To make unique haploid gametes
84
Describe what happens during prophase 1 of meiosis
- homologous chromosomes align and synapse
- crossing over occurs between non-sister chromatids at the chiasmata
- centrosomes form early mitotic spindles and move towards each cell pole
85
Describe what happens during metaphase 1 of meiosis
- Paired homologous chromosomes move to the metaphase plate
| - The chiasmata line up on the metaphase plate
86
What is the chiasmata?
the point at which crossing over and exchange of genetic material occur between the strands of homologous chromosomes
87
Describe what happens during anaphase 1 of meiosis
- recombined homologous chromosomes separate
| - sister chromatids remain attached
88
Describe what happens during telophase and cytokinesis of meiosis 1
- the haploid cells with duplicated chromosomes (the pair of sister chromatids) form
- they are haploid because only half the genetic information is in each cell
89
After telophase and cytokinesis of meiosis 1, are the cells diploid or haploid
Haploid because they only have half the genetic information in each cell
90
Meiosis || is the same as
mitosis
91
How does sexual reproduction produce genetic diversity?
- independent assortment of chromosomes
- crossing over
- random fertilisation of gametes
92
What is segregation and how does it increase sexual diversity?
Alleles segregate randomly into each gamete. When gametes are formed, each allele of one parent segregates randomly into the gametes, so half of the parent's gametes carry each allele.
93
What is independent assortment and how does it increase sexual diversity?
It is random whether a homologous pair of chromosomes lines up maternal:paternal or paternal:maternal which means that alleles of two different genes get sorted into gametes independently of one another.
94
What is crossing over and how does it increase sexual diversity?
The exchange of genetic material between non-sister chromatids of homologous chromosomes at the chiasmata during meiosis, which results in new allelic combinations in the daughter cells.
95
Crossing over creates new variations of
linked genes
96
Independent assortment creates new variations of
unlinked genes
97
What is aneuploidy? Give an example
An abnormal number of a particular chromosome
| eg. trisomy 21 (3 copies of chromosomes 21) causing Down Syndrome
98
What can cause Down Syndrome?
Non-disjunction
99
What is non-disjunction?
the failure of chromosomes to correctly separate during meiosis (could be the first or second division)
100
What are the sex chromosomes for an individual with Klinefelter Syndrome?
XXY
101
What are the sex chromosomes for an individual with Turner Syndrome?
XO
102
If a pair of chromosomes fails to disjoin at anaphase of meiosis |, what will be the likely chromosomes numbers (N) for the four resulting gametes?
N + 1
N + 1
N - 1
N - 1
103
What is polyploidy?
Possession of multiple sets of chromosomes
104
What are 6 chromosomal abnormalities?
1. non-disjunction
2. aneuploidy
3. deletion
4. duplication
5. inversion
6. translocation
105
Describe a deletion chromosomal abnormalities
The removal of a chromosomal segment
| eg. ABCDEFG is now ABCEFG
106
Describe a duplication chromosomal abnormalities
the repeating of a segment
| eg. ABCDEFG is now ABCBCDEFG
107
Describe an inversion chromosomal abnormalities
the reversal of a segment within a chromosome
| eg. ABCDEFG is now ADCBEFG
108
Describe a translocation chromosomal abnormalities
The movement of a segment from one chromosome to a non-homologous chromosome
eg. ABCDEFG and MNOPQR are now MNOCDEFG and ABPQR
109
Give an example of a syndrome caused by a deletion
Lejeune syndrome/Cri du chat caused by the deletion of the short arm of chromosome 5
110
Give two examples of conditions caused by an inversion
Philadelphia translocation t(9;22) which means that some of chromosome 22 and chromosome 9 have swapped over. This can cause myeloid leukemia
Or Familial Down syndrome from t(14;21) where a bit of 21 has broken off and joined with 14 and the rest of 21 has broken off and disappeared. If paired with a normal gamete, trisomy 21 can occur (Down syndrome)
111
Why does the lagging strand have to be synthesised as smaller fragments and what are these fragments called?
They have to be synthesised as smaller fragments so that they can be synthesised in the 5` -> 3` direction, despite this being opposite to the required direction. These fragments are called Okazaki fragments
112
In DNA replication, why is the primer removed and replaced?
Because the primer is RNA and it needs to be DNA
113
Where does DNA replication start?
At the Origin of Replication (OoR)
114
How many OoR does a human have and why?
A eukaryote has many OoR because replication is faster if it occurs simultaneously in many different locations rather
115
What is "the flow" of the Central Dogma of Molecular biology; what are the macromolecules and what is their function?
It outlines the process of how information coded for in DNA can flow in proteins. This process is described in two stages; transcription and translation.
116
What are the three stages of transcription?
Initiation
Elongation
Termination
117
What macromolecule is being synthesised in transcription and in which direction is the synthesis proceeding?
RNA is synthesised in the 5' -> 3' direction
118
What is transcription?
the process of converting DNA into RNA
119
What is translation?
the synthesis of proteins by ribosomes using mRNA as a set of instructions
120
What is the template for transcription and in which direction does it run?
DNA contains both a complementary strands: coding strand (5’ -> 3’) and a template strand (3’ -> 5’). The coding strand is the strand that contains the information that codes for a protein. The template strand is the one that is used during transcription so when mRNA bases are added complementary to the template strand, the mRNA will be identical to the required coding strand.
121
What happens during initiation of transcription?
- RNA polymerase || binds to the DNA strands at the promoter region and separates the two strands.
- this forms a transcriptional initiation complex
- RNA pol || contains a 3’ OH group which means that it can start mRNA synthesis without the use of a primer.
122
What happens during elongation of transcription?
- RNA pol || separates only about 20 or 30 nucleotides and moves along the template strand (running 3’ -> 5’), adding complementary mRNA bases in the 5’ -> 3’ direction.
- Instead of adding Thymine complementary to Adenine, RNA pol || adds Uracil.
123
Which parts of a gene is transcribed from DNA to mRNA?
The coding sequence and the UTRs
124
Which parts of a gene are translated from mRNA to protein?
The exons of the coding sequence
125
What is the promoter region?
The DNA segment recognised by RNA polymerase to initiate transcription
126
What are the 5' and 3' UTRs?
UnTranslated Regions
- contain regulatory elements that influence gene expression at the transcriptional and translational level
- transcribed but not translated
127
What is the 5'G cap and what is its function?
A region prior to the 5' UTR
- it prevents mRNA degradation
- regulates translation by providing ribosome binding site
128
What is the Poly-A tail and what is its function?
A region after the 3' UTR
- it prevents mRNA degradation
- regulates translation
- regulation of nuclear export
129
Explain the process of splicing
- The coding sequence consists of sections called exons and introns
- during splicing, the introns are removed
130
Briefly outline the process from DNA to protein
1. UTRs and coding sequence (both introns and exons) undergo transcription
2. this forms precursor mRNA
3. the pre-mRNA undergoes slicing and the introns are removed from the coding sequence
4. mature mRNA is formed
5. the mRNA undergoes translation to form a protein
131
How many codons are there?
64
132
What is a codon?
Three DNA bases that codes for one amino acid
133
How many of the 64 codons code for an amino acid? What are the other codons for?
61
| The other three are stop codons
134
What are the three stop codons?
UAA, UAG, UGA
135
What is the one start codon?
AUG
136
What amino acid is the first one in a peptide sequence?
Methionine (MET)
137
What binds to the mRNA codons and to the mRNA stop codons?
tRNA
138
Describe the tRNA molecule
- single strand of RNA
- 70-80 nucleotides in length
- at least one tRNA for each amino acid
- each tRNA has a region which can bind an amino acid and a region which can interact with mRNA
139
How can tRNA bind to an amino acid and interact with mRNA?
At one end there is an amino acid attachment site and at the other end, there is an anticodon which is complementary to the mRNA
140
What is meant by "charging the tRNA"?
Attaching an amino acid to the tRNA
141
Explain how the tRNA is charged
an enzyme recognises both the specific amino acid and the correct tRNA for this acid and joins them together
142
How many different tRNA molecules are there?
20 (one for each amino acid)
143
How many different amino acids are there?
20
144
Describe the anatomy of the ribosome
- it has a large subunit and a small subunit
- it has three sites (E, P, A)
- it has an mRNA binding site
- it has an exit tunnel
145
What is the purpose of the A site?
it is the aminoacyl tRNA binding site
146
What is the purpose of the E site?
It is the exit site
147
What is the purpose of the P site?
it is the peptidyl-tRNA binding site
148
Where are the ribosomes located?
Bound to the rough endoplasmic reticulum
| free in the cytosol
149
What are the tree stages of translation?
Initiation
elongation
termination
150
Describe initiation of translation
- 5'G cap is at the 5' end of the mRNA and this is where the ribosome binds with the mRNA
- the small ribosomal subunit recognises G cap
- small subunit latches onto mRNA and scans it until it finds the AUG (start) codon
- the tRNA charged with the Met amino acid and complementary anticodon binds to the P site
- large subunit attaches
151
Describe elongation of translation
- the tRNA carrying the next amino acid (eg. leu) enter through the A site
- two things at the same time:
1. Transfer one amino acid from tRNA in P site onto newly arrived amino acid on A site but the tRNA do not move
2. AT THE SAME TIME: the RIBOSOME moves three nucleotides ie. One codon along. Therefore the tRNA are now in the E and P sites. tRNA with chain is now in the P site and the empty one can leave through the E site
Bond between amino acids = peptide bond (strong)
152
Where do the tRNA enter the ribosome?
The first tRNA carrying Met comes through the P site and all the others come through the A site
153
What does polymorphic means?
one gene that has many different alleles
154
What is incomplete dominance?
When the heterozygous genotype codes for an intermediate phenotype that is a blend of the two phenotypes
eg. red and white giving pink
155
What is co-dominance?
When both phenotypes exist side by side within an organism
| eg. red and white giving red with white spots
156
What are polygenic traits?
when the phenotype is controlled by many genes that have an additive effect so the characters appear continuous or quantitive
157
Give 5 examples of polygenic traits
1. skin colour
2. weight
3. IQ
4. wool length
5. height
158
Describe the additive effect
the phenotype is determined by a number or alleles which could be 0 (and you could be white eg.) or 6 (and you could be black)
159
Apart from the genotype, what else can affect the phenotype?
The environment
160
What is an allopolyploid?
When two species interbreed to produce a new hybrid with chromosomes from each parent species. The hybrid is infertile because the chromosomes do not pair up (even if each species produces a gamete with the same number of chromosomes). To become sterile, a mitotic disjunction (chromosome doubling event) must occur
161
What is lyonization?
The inactivation of an X chromosome in females during early embryonic development
162
Why are females stripey?
In females during early embryonic development, one of the X chromosomes is inactivated in each cell and therefore some cells will show the phenotype of the X from dad and some will show the phenotype of X from mum.
163
What are the building blocks of DNA?
nucleotides
164
What are the three components of the building blocks of DNA?
A base (A,C,T or G), a phospate and deoxyribose sugar.
165
There are two types of bases; what are they called and how many "rings" are there in each?
Pyrimidines (1 ring)
| Purines (2 rings)
166
Give two examples of a pyrimidine
Cytosine and Thymine
167
Give two examples of a purine
Adenine and Guanine
168
How does the sugar component in a DNA and RNA molecule differ?
The sugar component of DNA is deoxyribose with an H on the second carbon and for RNA it is ribose with and OH on the second carbon
169
How do the bases in DNA and RNA differ?
DNA: C,G,T,A
RNA: C,G,U,A
170
With what type of bond are DNA and RNA nucleotide monomers joined together?
A phosphodiester bond
171
Particular carbons and chemical groups are involved in joining the nucleic acid monomers together. Which ones?
One nucleotide contains a base, a phosphate group and a sugar.
The 5th carbon (the 5' end) is bonded to the phosphate group. This phosphate is bonded to the 3rd carbon (the 3' end) of the next nucleotide's sugar. The bond between the 3' and phosphate is the phosphodiester bond.
172
How many polynucleotide chains make up a DNA molecule and how are these organised in relation to each other?
There are two chains arranged in an antiparallel arrangement
173
In which direction does a DNA chain grow when it is being synthesised?
From the 5' to 3' direction
174
How is the DNA helix stabilised?
(be specific; which component of the nucleotide is involved and include the type and number of bonds between these components)
By hydrogen bonds between the bases of the two strands.
| There are 3 H bonds between C and G and 2 H bonds between the T and A
175
What nucleotide components are located on the inside of the DNA helix?
The bases
176
What nucleotide components are located on the outside of the DNA helix?
The phosphate group and the sugar making a phosphate sugar backbone
177
What kind of replication does DNA undergo?
Semi-conservative
178
What were Chargaff's significant findings?
- the amount of A bases was the same as the T bases and the amount of C bases was the same as the G bases
The composition of DNA varies between species
