Unit 4 AoS1 INHERITANCE Flashcards
(168 cards)
1
Q
What is a gene?
A
Definition: A gene is a short section of DNA that codes for a specific polypeptide/protein.
A gene is a unit of inheritance made up of DNA and usually codes for a protein. (Can code for more than one protein [alternative splicing])
2
Q
What is the locus?
A
The position of the gene on a chromosome
3
Q
What happens in transcription?
A
- DNA unwinds and unzips, exposing DNA nucleotides on the template strand.
1) Pre-mRNA is synthesised by RNA Polymerase from the DNA that codes for the gene by joining of complementary RNA nucleotides (complementary to DNA template strand)
2) Introns are spliced, methylated cap is added to 5’ end, poly-A tail added to 3’ end.
3) Mature mRNA formed leaves the nucleus
4
Q
What happens in translation?
A
1) Ribosomes read mRNA strand from 5’ to 3’ end
2) tRNA brings specific amino acids to the ribosome.
3) Anticodon of tRNA is complementary to triplet codon on mRNA
4) Peptide bonds are formed between amino acids and polypeptide is formed.
5
Q
Promoter
A
part of the upstream flanking region of a gene containing base sequences that control activity of that gene (where RNA polymerase binds to)
6
Q
Coding region
A
part of a gene that contains coded information for making a polypeptide chain
7
Q
Exon
A
part of the coding region of a gene that is transcribed and translated
8
Q
Intron
A
part of the coding region of a gene that is transcribed but not translated
9
Q
What are the pre-mRNA modifications after transcription?
A
1) Introns in the coding region are spliced out (producing shorter mRNA molecule)- Splicing
2) Pre-mRNA is chemically capped [methylated cap] (at the 5’ end) to prevent mRNA from being degraded by enzymes like ribonucleases.
3) Poly-A tail is added (at 3’ end)
10
Q
Spliceosomes
A
Enzymes that cut out the introns
11
Q
Alternative splicing
A
- Many genes can produce more than one protein because the mRNA transcript can contain different combinations of exons.
- Through alternative splicing, number of outputs from genetic instructions (genes) in a genome is far greater than number of genes
12
Q
What is intron retention?
A
Can produce different mRNA molecules from the same pre-mRNA, depending on whether or not all the introns are cut out and discarded
13
Q
What is exon juggling?
A
Can produce different mRNA molecules from the same pre-mRNA, depending on whether or not all the exons are used in final mRNA
14
Q
What is point mutation?
A
Point mutation or single base substitution- type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material
15
Q
A disease caused by point mutation?
A
Sickle- cell anaemia
16
Q
What are the two major types of point mutations?
A
Substitution point mutations and frameshift mutations
17
Q
What are the types of substitution point mutations?
A
- Missense- different amino acid results after the mutation has taken place
- Neutral/silent- Same amino acid coded for after mutation
- Nonsense- protein synthesis stops (due to a mutation leading to a stop codon i.e from UAU –> UAA)
18
Q
Types of frameshift mutations?
A
- Deletion- a single nucleotide is deleted from the sequence- results in a shift in ‘frame’
- Insertion- a single nucleotide is inserted into the sequence- results in a shift in ‘frame’
19
Q
Haploid
A
(of a cell or nucleus) having a single set of unpaired chromosomes.
*In humans–> sex cells have 23 chromosomes
20
Q
Diploid
A
(of a cell or nucleus) containing two complete sets of chromosomes, one from each parent.
*In humans–> somatic cells have 46 chromosomes
21
Q
What is a genome?
A
Definition: the total genetic material (full set of genes) found within a cell or individual.
- each species has a unique genome–> organisms of the same species (ie humans) have the same genome.
- All the genetic information found in one set of an organism’s chromosomes (ie total amount of DNA in a haploid cell (gamete) in eukaryotes/ or the singular chromosome in prokaryotes)
22
Q
What is a housekeeping gene and what are some examples?
A
Genes which are switched on in all cells
Examples:
*Enzymes required for respiration
*Proteins required in structure of plasma membranes
*Proteins required for cellular respiration (cytochrome c) in eukaryotic cells
23
Q
What are some advantages of regulating genes and gene expression?
A
- To conserve energy and materials by blocking unnecessary gene expression
- To prevent production of enzymes for a nonexistent substrate
- To prevent overproduction of a protein
- Thus the cell can control its own metabolism- resources are only used when there is a metabolic need, resources can be redirected to other metabolic pathways
24
Q
Repressors
A
Proteins that stop the transcription of genes e.g. Lac Operon
25
Activator Proteins
Proteins that start or increase the rate of transcription of genes so that more proteins are produced. e.g. the CAP protein
26
What is the regulatory gene?
A gene that produces a protein (i.e. regulatory proteins) that controls whether the promoter region is switched on.
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The coding region (structural gene)
The DNA sequence that will be transcribed from the template strand
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The terminator region
Downstream flanking region of gene
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Operator region
Where regulatory protein (repressor protein) binds to
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What does it mean if a gene is expressed?
Gene is turned 'on'--> Transcription --> Translation --> Protein production
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Types of regulatory proteins?
Activator proteins
| Repressor proteins
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Types of genes that repressor proteins act on?
Inducible genes- always turned off, but they can be turned on e.g. lac operon
Repressible genes- always turned on, but they can be turned off e.g. tryp operon
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Difference between structural and regulatory genes?
Structural genes: produce proteins and become part of the structure and functioning of the organism.
Regulatory genes: produce proteins that control the action of other genes, eg they turn other genes on or off. These proteins can bind directly to DNA, or may bind to receptors which stimulate signal transduction.
34
What is the lac operon?
a set of genes in bacteria used for lactose metabolism
35
Regulation of the lac operon in bacteria?
Lactose --B-galctosidase--> Galactose + Glucose
Lactose present – The gene for B-galctosidase is transcribed
No lactose present- no need for B-galactosidase so gene is not transcribed
36
What happens in the absence of lactose in the lac operon (inducible gene)?
1) Active repressor protein binds to operator region,
2) This prevents RNA Polymerase from binding to the promoter region
3) No transcription takes place--> gene is turned off
4) The lac operon is not transcribed, and no beta-galactosidase is made.
37
What happens in the presence of lactose (inducer) in the lac operon (inducible gene)?
1) Lactose binds to active repressor protein, changing its conformational shape and making it inactive
2) Repressor protein is unable to bind to operator region
3) RNA Polymerase is able to bind to promoter region
3) Transcription takes place--> gene is turned on
38
What happens in the absence of tryp in the tryp operon (repressible gene)?
1) Inactive repressor protein is unable to bind to operator region
2) RNA Polymerase can bind to the promoter region
3) Transcription takes place--> gene is turned on
39
What happens in the presence of tryp in the tryp operon (repressible gene)?
1) Tryp acts as a corepressor and binds to the inactive repressor protein, changing its conformational shape and making it active
2) Active repressor protein binds to the operator region
3) RNA Polymerase is unable to bind to the promoter region
4) No transcription takes place--> gene turned off
40
What is a microarray and what is it used for?
A microarray is a set of DNA sequences representing the entire set of genes of an organism, arranged in a grid pattern for use in genetic testing.
It is used to determine which genes are active and which genes are not.
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How do microarrays work?
* Segments of DNA are placed in small wells and made into single stranded DNA.
* mRNA is isolated from the cells the scientist is interested in (this is produced by transcription so shows that the complementary DNA was expressed/turned on)
* mRNA converted to cDNA using reverse transcriptase (enzyme) (fluorescent dyes used as markers)
* fluorescent single stranded cDNA is used as probes to bind with single stranded DNA in the wells from the organism
* fluorescent cDNA lights up the wells with the DNA that is being expressed
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Factors that affect gene regulation?
* the age of the organism
* the location of the cell or organism
* the presence or absence of regulatory proteins/ substances
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Function of restriction enzymes?
Cuts DNA into fragments at precise, specific locations known as recognition sites.
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Purpose of gel electrophoresis?
DNA fragments can be sorted, according to their lengths.
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Purpose of DNA ligase enzyme?
Catalyses the joining of pieces of double-stranded DNA at their sugar-phosphate backbones (strong covalent bonds)
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What is a probe?
* A single-stranded segment of DNA which is (radioactively) labeled.
* Commonly, a piece of single stranded DNA (or RNA) with a base sequence that is complementary to the base sequence in one of the strands of target DNA.
* Target DNA must be denatured to separate its two strands- otherwise probe cannot pair with it.
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What is the purpose of a probe?
To pick out one particular DNA fragment from a large number of DNA fragments.
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What is a DNA ladder?
A solution that contains DNA fragments of known lengths and is used to compare against the bands obtained to determine size of DNA, in gel electrophoresis.
*Must be placed in the same gel, because differing factors can affect the rate of movement of bands.
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General process of gel electrophoresis?
1) Dissolved DNA fragments placed at one end of jelly-like supporting material (gel)
2) Gel is exposed to electric field with positive pole at far end and negative pole at starting end
* DNA is negatively charged because of phosphate group in sugar-phosphate bond
3) End result: Series of parallel bands of DNA fragments appear at differing distances down the gel
4) Size of unknown bands are known by comparing distance moved against fragments of known sizes (standard or DNA ladder)
* Bands can run at different speeds depending on factors like pH and temperature
* Important Note: smaller bands move towards positive charge much quicker than larger bands
50
How does a probe work?
* The base sequence of the probe is complementary to part of its target.
* A probe carries a radioactive or fluorescent label, represented by the flag, so that it (and its target) can be located.
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How can DNA be transported into a cell?
Through use of a vector e.g. plasmid
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What does gene cloning involve?
* Gene cloning involves the incorporation of foreign genes into plasmid genes which can then replicate
* Example: To produce large numbers of human insulin by E. Coli bacterial cells
53
What are the general steps in gene cloning?
1) Cut the target DNA with gene of interest using restriction enzyme.
2) Cut plasmid vector with the SAME restriction enzyme so that complementary sticky ends are produced.
3) Join cut target DNA and plasmid vector with DNA ligase --> recombinant plasmid
4) Transformation of bacterial cells by making them competent (additon of CaCl2) and then using heat/electric shock-- > pores form on cell membrane through the heat or shock that allows the recombinant plasmid to enter.
5) Identify transformed bacteria. Allow bacteria and plasmid to self replicate under optimum conditions.
54
How are the transformed bacterial cells (in gene cloning) identified?
* When a bacterial plasmid (plasmid vector) is chosen, it should have an antibiotic resistance gene e.g. resistance to ampicillin
* The location of the inserted gene and the antibiotic resistance genes determine the growth of the bacteria on agar plates with antibiotic.
55
What is a transgenic organism?
Organisms that carry one or more genes artificially introduced from another species e.g. E.coli carrying the human insulin gene
56
What is the purpose of polymerase chain reaction?
To amplify (make multiple copies of) a segment of DNA.
57
PCR involves what?
PCR involves repeated cycles of:
1) Denaturation 95 degcel
2) Annealing 55 degcel
3) Extension 72 degcel
58
What "ingredients" does PCR require?
* Taq DNA Polymerase (enzyme)
* Primers (short pieces of synthetic single stranded DNA which is a pre existing nucleotide chain for the DNA polymerase to build on)
* A supply of nucleotides
59
What happens during denaturation during PCR?
* Hydrogen bonds break between complementary DNA strands
| * DNA strands separate
60
What happens during annealing during PCR?
* Addition of primers (attach with hydrogen bonding)
| * Primers complementary base pair with region spanning the target DNA
61
What happens during extension in PCR?
* Taq DNA polymerase copies the DNA strands, starting with primers (extension at 72 degcel for one minute)
* Taq DNA polymerase adds complementary base pairs to template strand.
62
What is hybridisation?
* Hybridisation is when DNA samples from two different species are denatured, mixed and then allowed to anneal. The result is DNA in which one nucleotide chain is from one species and the other chain is from another species.
* The process of forming a double stranded DNA molecule between a single stranded DNA probe and a single stranded target DNA.
63
Describe the process of DNA Sequencing?
Automated Sequencing
Fluorescent nucleotides are added to a test tube with normal nucleotides, DNA to be sequenced and DNA polymerase. The DNA is heated to separate the complementary strands. DNA polymerase then adds complementary nucleotides to form a complementary strand. When the fluorescent nucleotides are added it causes DNA polymerase to stop synthesis. This happens randomly, so you get fragments of all sizes which finish with their respective fluorescent dye.
The fragments are then run in a single lane on a gel in the automated sequencing machine, which records the colour of the fragments as they move through - the shortest fragments move the fastest towards the positive electrode. This is then converted to a print out that can easily be read from left to right.
64
Steps in DNA profiling?
1) DNA is cut into fragments by restriction enzymes
2) DNA fragments are separated into bands by electrophoresis- there is also standard of comparison (DNA ladder)
3) DNA band pattern on electrophoretic gel is transferred to nylon membrane
4) Nylon membrane with DNA fragments positioned exactly as they were on gel
5) A radioactive probe is added to membrane where it binds to specific fragments
6) X-ray film is placed next to the membrane to detect the radioactive
7) Developed X-ray film, showing DNA fragments that combined with the radioactive probe
65
What is the purpose of DNA/gene sequencing?
In order to identify order of nucleotides across a gene.
66
What is the aim of gene manipulation/ DNA manipulation?
To isolate desirable genes in one cell and move the gene to another cell. The movement of genes can be within a species or to another species to form transgenic organisms.
67
What can mutations be caused by?
Mutations are cussed by environmental agents such as:
* ultraviolet radiation,
* X Rays,
* nuclear radiation and
* certain chemical agents.
>>the effects of chemical mutagenic agents may depend on their concentration and length of exposure.
68
Name two types of functions of genes and explain whether all genes are responsible for the production of a protein.
Genes can have one of two major functions:
* 'Structural genes' are directly responsible for a protein that is part of an organism's structure or has a function.
* 'Regulator genes' control the action of other genes by determining whether a gene is active or not. In this way, the rate of production of particular materials can be controlled.
69
Examples of the use of PCR?
* useful for forensic tests when small tissue samples may remain.
* used in prenatal diagnosis to produce enough DNA to analyse for genetic abnormalities.
70
What is an allele?
Definition: An allele is a gene that controls one function but can exist in different or varying forms. Alleles code for traits (characteristics).
*the alternative forms of a gene are called alleles--> they differ in base sequence of the gene/location.
71
What determines the number of chromosomes in a cell?
The number of centromeres in a cell.
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What are homologous chromosomes?
Homologous (literally meaning same locus) chromosomes are chromosomes of the same size that:
- have the same genes located in the same loci
- have the same centromere position
- have the same banding pattern
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What are somatic cells?
```
Body cells (cells other than germline cells)
*usually contain a diploid number (2 sets) of chromosomes.
```
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What is a gamete?
Sex cells that contain a single set of chromosomes (unpaired chromosomes).
*An egg or sperm is said to haploid
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What is a proteome?
The total protein complement that can be translated by a cell or an individual organism.
*differs for each individual--> tissue differences
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What is a karyotype?
A graphic display of the complete set of chromosomes from a cell of a particular organism.
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What are the two types of chromosomes typical of eukaryotic cells?
1) autosomal chromosomes (autosomes) form homologous pairs which do not differ between the sexes
2) sex chromosomes determine the sex of a organisms, forming a homologous pair in one sex (eg XX) and a dissimilar pair in the other (eg XY)
* genes for all gender characteristics only found on sex chromosomes
* both autosomes and sex chromosomes carry genes coding for features unrelated to sex.
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What happens during interphase?
```
Interphase occurs prior to mitosis. All organelles increase in number and DNA is replicated during this phase.
Interphase includes:
1) G1 phase (gap 1 phase)
2) S phase (synthesis)
3) G2 phase (gap 2 phase)
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What happens during G1 in interphase?
* Cell doubles in size
* Organelles, enzymes and other molecules increase in number.
* Undifferentiated cells undergo cell differentiation and cell specialisation.
* Most cells undergo apoptosis (due to a gene being activated) but some cells go onto Synthesis stage (next stage)
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What happens during synthesis (S phase)?
* DNA and associated proteins replicate; 2 copies of the cell's genetic information now exist.
* The enzyme DNA Polymerase uses free nucleotides to synthesise new DNA strands
* Chromosomes are not visible (during interphase)
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What happens during G2 (gap 2 phase)?
* Structures required for cell division begin to assemble.
| * Chromosomes begin to condense. (Only after the chromosomes have condensed sufficiently do chromatids become visible.)
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What are chromatids?
Chromatids are the two strands of a replicated chromosome which are joined together by a single centromere.
*They separate at anaphase of mitosis and anaphase II of meiosis to become daughter chromosomes.
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What are the four phases of mitosis in a cell? (2n=4)
Prophase
Metaphase
Anaphase
Telophase
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What happens during prophase in mitosis?
* Chromosomes shorten and thicken (condense)
* In animal cells, centrioles move to the poles.
* Nucleus disappears as chromosomes continue to shorten and thicken
* Chromatids become distinct
* Spindle fibres begin to form--> chromosomes attach to spindle fibres (centromeres)
85
What happens during metaphase?
* Chromosomes are arranged along the equator (middle) of the cell in a single file.
* Each chromosome is attached to a spindle fibre by the centromere. (On own spindle fibre not in pairs)
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What happens during Anaphase?
* The chromatids split (perform disjunction) at the centromere.
* Daughter chromosomes migrate to either end of the cell
* Spindle fibres begin to disappear
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What happens during telophase?
* Cytoplasm begins to constrict
* Cell starts to pinch in half (in animal cells)
* Cell plate forms in plant cells
* Spindle fibres disappear
* Nucleus reappears and chromosomes are no longer visible
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What happens during cytokinesis?
Follows telophase (not part of mitosis)
* the cytoplasm is divided into two cells.
* in animal cells, a cleavage furrow forms between dividing cells at cytokinesis.
* in plant cells, a cell plate forms from materials supplied by Golgi vesicles-->ultimately forms a cell wall.
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What is the purpose of mitosis?s
Mitosis ensures that cells maintains large surface area to volume ration.
It allows for:
-Growth of an organism
-Replacement of cells which have died or been damaged.
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What is asexual reproduction? Give examples.
Does not involve the fusion of two gametes.
*The alleles (Genotypes) of the parent and offspring are identical
*Involves some type of DNA replication
Examples: binary fission in bacteria, plant division using cuttings, bulbs etc
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What is sexual reproduction?
Involves the fusion of gametes (typically produced during cell division called meiosis)
92
Define co-dominance.
The full effects of both alleles are visible in the phenotype of the heterozygote.
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Define incomplete dominance.
The partial effects of both alleles are visible in the phenotype of the heterozygote.
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What does 'dominant' refer to?
The phenotype observed in the heterozygous individual.
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What does the term 'recessive' refer to?
The phenotype that is not observed in the heterozygous individual.
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What does the term homozygous refer to?
Both of the alleles are the same, eg AA or aa
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What does the term heterozygous refer to?
The alleles in the genotype are different eg Aa
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What is the genotype?
The combination of alleles(eg AA, Aa or aa) for a particular gene in an organism
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What is variation?
The differences between organisms.
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What is the phenotype?
Characteristics of an organism based on their genotypes (expression of their genes) and the environment.
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What does 'wild type' refer to?
The most common phenotype for a particular trait.
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What does 'mutant' refer to?
Any phenotype that is not the most common for a particular trait.
103
A plant that is tall can either be homozygous (TT) or heterozygous (Tt). How can its genotype be determined?
1) Do a test cross by crossing with a homozygous recessive dwarf plant (tt)
2) If all offspring are tall, then the plant is most likely to be homozygous dominant (TT)
3 If 50% of the offspring are dwarf plants (or at least one of the offspring is dwarf, then the tall plant is heterozygous (Tt).
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What is an autosomal trait?
A trait coded for by a gene located on an autosomal chromosome.
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What is a sex- linked trait?
Genes on sex chromosomes code for sex-linked traits.
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What are unlinked genes?
Genes found on different chromosomes.
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What are linked genes?
Genes that are (close together) on the same chromosome.
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An easy way to identify whether a trait is most likely autosomal dominant in a pedigree?
Two affected parents have at least one unaffected child.
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An easy way to identify whether a trait is most likely autosomal recessive in a pedigree?
Two unaffected parents have at least one affected child.
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An easy way to identify whether a trait is most likely X-linked dominant in a pedigree?
If fathers are affected, daughters will always be affected.
* General trend: more females than males affected.
* *If pedigree shows that affected father has unaffected daughter --> RULE OUT X-LINKED DOMINANT.**
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An easy way to identify whether a trait is most likely X-linked recessive in a pedigree?
If mothers are affected, sons will always be affected.
* *General trend: more males than females affected**
* *If pedigree shows that affected mother has unaffected son--> RULE OUT X-LINKED RECESSIVE**
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An easy way to identify whether a trait is most likely Y-linked in a pedigree?
Affected fathers always have affected sons.
| TRAIT IS ONLY SEEN IN MALES!
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What is meiosis?
A type of cell division that occurs in sex organs that results in gametes.
114
What ratio are the results in for linked genes?
Phenotypic ratio other than 1:1:1:1
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What are polygenes?
Genes involved in polygenic inheritance (characteristic controlled by more than one gene) which are typically located on different chromosomes.
116
What is discontinuous (discrete) variation in a population?
When members if a population can be grouped into a few discrete and non overlapping classes of a trait. E.g. Number of fingers, pink or red snapdragons or flat toenails.
*Discontinuous variation is determined by a single gene. (Monogenic)
117
What is continuous variation?
Variation that results in characteristics which exhibit a continuous range of phenotypes across a population. E.g. Height, skin colour, eye colour
*Caused by polygenes (many genes working together to produce the trait.
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What is chromatin?
The DNA and protein making up the chromosome is known as chromatin.
*in order to fit within a cell, chromosomes contain supercooled chromatin.
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What is an autosome?
Chromosomes other than sex chromosomes that form homologous pairs which do not differ between the sexes.
120
What is a sex chromosome?
Chromosomes that determine the sex of organisms, forming a homologous pair in one sex (eg XX) and a dissimilar pair in the other (eg XY)
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What is a karyotype?
A graphic display of the complete set of chromosomes from a cell of a particular organism. Chromosomes are typically arranged in pairs.
122
What is the law of independent assortment?
The behaviour of each pair of genes(chromosomes) is not influenced by the behaviour of other pair of genes (chromosomes).
**ONLY if the genes' loci are on different chromosome pairs.
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Pure breeding
An organism when crossed with itself or others like it, always produces offspring like itself, ie it is homozygous.
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What is the tryp operon?
a group of genes that are used, or transcribed, together — that codes for the components for production of tryptophan. The trp operon is present in many bacteria, but was first characterized in Escherichia coli.
125
What is codominance?
Both alleles in the genotype are expressed equally in the phenotype. e.g ABO blood group gene.
126
What are the two purposes of a test cross?
1) To determine whether the dominant phenotype is homozygous or heterozygous. (in the case of a monohybrid cross)
2) To test for gene linkage: double heterozygote X double homozygous recessive (in the case of a dihybrid cross) (UNLINKED genes have phenotypic ratio of 1:1:1:1)
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What is a test cross?
A cross between an individual with the dominant phenotype and an individual with a homozygous recessive phenotype.
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What is the F1 cross?
The cross between two homozygous parents to produce a heterozygous offspring.
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What is the phenotypic outcome of a dihybrid F2 cross (e.g. RrYy X RrYy) ?
9:3:3:1 phenotypic ratio
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What is X inactivation in females?
X inactivation happens during embryonic development in order to equalise the dosage of proteins that both males and females get. (One X chromosome is inactivated)
131
What is the purpose of a reciprocal cross?
To determine if a characteristic is sex-linked or not.
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Why are the parental classes greater than the recombinant classes in a test cross with linked genes?
Parental classes have the largest proportions of phenotypes because they are a result of parental gametes, which are produced in high proportions as the alleles that are close together, tend to be inherited together.
Recombinant classes have the lowest proportions of phenotypes as they are a result of crossing over and recombination which is less likely to occur when genes are linked.
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What is a pedigree?
A family tree that shows the frequency and occurrence of particular phenotypes (hence alleles) over many generations.
134
What are plasmids?
Small, circular DNA molecules found in many bacteria in addition to their chromosome.
*They are self replicating--> used in gene cloning to make multiple copies of desired genes.
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What is reverse transcriptase?
An enzyme that synthesises DNA from an RNA template i.e. it performs the reverse of transcription found naturally in retroviruses)
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What are methods of gene transfer?
* Retroviruses
* Liposomes
* Microinjection
137
Why do smaller/shorter fragments migrate towards the positive electrode faster in gel electrophoresis?
Due to their reduced level of friction with the pores in the gel, that allows for their speedy movement.
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What is the purpose of southern blotting?
Process used to separate fragments from each other in order to distinguish and identify individuals based on their DNA.
139
What is restriction fragment length polymorphism (RFLP) in alleles?
RFLPS are sections of DNA produced by cutting homologous DNA strands with specific restriction enzymes.
140
What are short tandem repeats (STRs) used in DNA profiling?
DNA sequences of 2-5 bases which repeat, one after the other, for different lengths in different individuals i.e from 2 to 100+ bases (e.g. CATCATCATCATCAT... etc)
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Purpose of DNA profiling?
Used in criminal investigations, genetic disease diagnosis etc
142
What does it mean if DNA is said to be universal?
In all organisms. the same triplet code (3 base code) codes for the same amino acid ie AAA. (transfer genes to another species/organism and the code will translate into the same amino acid ie insulin gene )
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What does term hemizygous refer to?
Having only a single copy of a gene instead of the customary two copies. All the genes on the single X chromosome in the male are 'hemizygous'.
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What is complete dominance?
The action of a single allele coding for the dominant trait (ie in genotype Tt) or two alleles coding for the dominant trait (ie TT).
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What is a chromosome?
THread like structures composed of DNA and protein and visible incells during mitosis and meiosis.
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What is recombination?
Process of generating new combinations of alleles of various genes both by crossing over and by independent assortment during meiosis.
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What is a monohybrid cross?
A cross in which alleles of only one gene are involved
148
What is a dihybrid cross?
A cross in which alleles of two different genes are involved.
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Transcription
The base sequences in the DNA (triplets) are transcribed onto an mRNA molecule as codons.
150
Translation
The base sequence (codons) of the mRNA is used to produce the amino acid sequence of a polypeptide chain which folds to become a protein.
151
Define monomorphic.
A species in which all individuals look alike. (i.e. insects, protozoa)
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Define polymorphic.
Existing in two or more different forms within a species or population
153
What is gene regulation?
The switching on and off of specific genes.
154
What is gene expression?
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. (ie proteins)
*These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
155
What is a mutation?
A mutation is a permanent change in the genetic material (or DNA sequence).
*Mutations can affect a single point in a gene, or larger sections of DNA (e.g. chromosomal mutations).
156
What are the features of the genetic code?
* Degenerate (redundant): More than one triplet code can code for the same amino acid.
* Unambiguous: A particular code can code for only ONE amino acid (ie TAC can code only for methionine and not any other amino acid)
* Universal: The codes code for the same amino acid in almost all living cells.
157
Blunt ends
In molecular biology, a blunt end may result from the breaking of double-stranded DNA; however, there are no overhangs or unpaired bases.
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Sticky ends
A fragment of DNA (often produced by a staggered cut on the DNA using restriction enzymes) in which the terminal portion has a stretch of unpaired nucleotides, and the strands are not of the same length. -->overhanging nucleotides.
159
What is a restriction enzyme?
A class of enzyme (found in bacteria) that cuts double-stranded DNA at sites that contain a particular base pair sequence recognition site.
160
What are the steps involved in DNA Replication?
* Helicase enzyme helps to separate the DNA strands. (Single stranded binding proteins helps to keep them separated)
* RNA primase synthesises an RNA primer to which DNA polymerase adds DNA nucleotides to.
* DNA polymerase always synthesises DNA from 5' to 3'direction.
* Leading strand is synthesised in a continuous direction.
* Lagging strand is synthesised in Okazaki fragments.
* RNA primers are removed and replaced with DNA by another DNA polymerase.
* DNA ligase joins all the DNA pieces together.
161
What are the steps involved in somatic cell nuclear transfer?
1) Isolate a somatic cell and transfer nucleus from that cell to an egg cell without a nucleus (enucleated egg cell)
2) The egg cell with the new nucleus acts like a zygote which develops into an embryo.
3) The embryo is then implanted into a surrogate mother and carried to term.
162
What are stem cells?
Cells that have the ability to differentiate into many different specialised cells.
163
What are the different types of stem cells?
* Totipotent: can give rise to all cell types (fertilised egg and cells of a 2- cell/4-cell/ 8-cell embryo.
* Pluripotent: can give rise to most cell types (cells from inner cell mass of an early embryo)
* Multipotent: can give rise to certain cell types (adult/somatic cells such as bone marrow stem cells)
164
What is non-disjunction at anaphase in meiosis?
Failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2, specifically in anaphase.
165
What does it mean if an event is aneuploidy?
If single chromosomes fail to separate during anaphase (I or II) in meiosis
Eg Down syndrome, klinefelter's syndrome, turner's syndrome
166
What does it mean if an event is polyploidy?
If complete set of chromosomes fail to separate
| Not viable in humans but often viable in plants
167
What are the different types of block mutations (chromosomal mutations)?
* Deletion
* Translocation
* Inversion
* Duplication
168
Differences between mitosis and binary fission?
Binary fission differs from mitosis as (two of)
the chromosome does not line up on the equator
the chromosome does not separate at the centromere
there are no spindle fibres
there are no phases; for example, prophase
it is quicker.
