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25 Cards in this Set
- Front
- Back
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Define the terms allele, autosome, centromere, chiasma, chromatid. chromosome
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Allele: A variation of a gene, each individual has 2 alleles for every gene which can either be the same or different.
Autosome: a chromosome other than the sex chromosome, 23 Centromere: The region of the dupilicated choromosome, after S phase, where the 2 chromatids meet. Also the site of attachement for microtubule spindle during cell division. Chiasma: Site of crossing over during meiosis where genetic material is exchanged between 2 chromatids. Method of variation all with indepedant alignment on metaphase equator. Only when this occurs between 2 non sister chromatids ( not homologous chromosomes) will be there be genetic consequence. Chromatid: one of 2 identical components of a duplicated chromosome, containing a single double stranded DNA molecules. Has a short p arm and a long y arm. Chromosome: A structure containing one DNA molecule prior to duplication and 2 identical DNA molecules after duplication. |
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Define dominant, gene, genotype, heterozygous, homozygous, locus
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Dominant: A phenotypic trait is dominant if it occurs in both homozygotes and heterozygotes.
Gene: a length of DNA on a chromosome that codes for a protein, a unit of heridity. Genotype: the genetic make up of an individual. Heterozyous: having 2 different alleles for a particular genetic locus Homozygous: having the same 2 allels for a particular genetic locus Locus: specific postion on a chromosome |
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Define meiosis, mitosis, phenotype, recessive, somatic cell, telomere.
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Meiosis: the process of cell division that produces gamets
Mitosis: the process of cell division that produces 2 identical daughter cells. Phenotype: all observable characteristics or traits of an individual as a result of genetic makeup of one or more genetic loci. Recessive: A phenotype is recessive when it occurs in homozygotes only Somatic cells: Diploid, 23 homologous pairs Gametes: Haploid, 23 chromosomes. Telomere: |
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Describe the process and roles of mitosis.
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Mitosis is the cellular division of somatic cells to form 2 daughter cells which are genetically identical to the parent cell. Stage of mitosis:
- prophase Breakdown of nuclear envelope, spindle fibres appear, chromsomes condense - Prometaphase Spindle fibres attach to centromere of chromosomes - Metaphase chromosomes align -Anaphase centromeres divide and sister chromatids move to opposite poles - Telophase Nuclear membrane reforms, chromosomes decondense, spindle fibres disappear - Cytokinesis Cytoplasm divides to form 2 daughter cells. Somatic cells need to divide in order to grow and for maintenance, to repair worn out or dead cells. In life some cells retain capacity to divide eg bone marrow cells and epidermal cells ( epithelia ) |
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Describe the proces and roles of meiosis.
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Meoisis is cellular division of a diploid cell, resulting in 4 haploid gametes ( spermatogenesis -> spematids and Oogenesis -> oocytes)
There are 2 stages of meoisis. Meosis 1 - Prophase I Chromosomes condense and homologous chromosomes pair up to form bivalent- crossing over, nuclear envelop and nucleolus disappears Metaphase I Spindle fibres attach to centromeres and bivalents randomly align on equator. Anaphase I Homologous chromosomes are seperated as each chromosome moves to opposite pole Telophase I Nuclear envelope reforms Meiosis 2 - formation of tetrad 2 cells -> 4 Prophase 2 Chromosomes condense and spindle reforms Metaphase 2 Random alignment of chromosomes on equator, spindles attach to centromeres Anaphase 2 Sister chromatids are seperated, moving to opposite poles as centromeres divide. Telophase 2 Nuclear envelope reforms, Nucleolus reappears, spindle fibres. Cytokinesis cytoplassm separate into 4 haploid cells. Roles of Meiosis are to produce gametes in spermatogenesis and oogenesis and so retain the same chromosome number generation to generation. Meiosis also creates genetic diversity by crossing over in prophase 1 - exchanging genetic material with homologue and by independent alignment of chromosomes and chromatids in metaphase |
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Distinguish clearly between genotype and phenotype
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Genotype is genetic makeup of an individual.
Phenotype are the observable characteristics or traits of an individual based on their genetic makeup of one or many genetic loci. Allele expression. Genotype causes phenotype and is affected by environment such as mutagens, radition, lifestyle, nutrition etc. Phenotype is caused by a combination of genotype and environment. |
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Explain how environmental factors have an influenece on both phenotype and genotype.
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Genotype causes phenotype and is affected by environment such as mutagens, radition, lifestyle, nutrition etc.
Phenotype is caused by a combination of genotype and environment. Cystic fibrosis is a disease caused solely by genotype. Infection is caused solely by environment eg overcrowding, contaminated water etc Diabetes, cardiovascular disease and cancer are caused by both as one might have a genetic predisposition to the disease or one might cause the disease by lifestyle choices eg diet, smoking, little exercise. |
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Distinguish between gene and allele.
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A gene is an heriditary unit. it is a length of DNA on a chromosome at a specific genetic loci that codes for a protein. More than one gene can be involved in producing a phenotype eg several genes code for several enzymes which may all be needed to achieve product. complementation when 2 homozygous mutated genomes breed to form mutant free individual - albinism.
An allele is a variation of a gene. Every individual has 2 alleles which might be the same- homozygous or different - heterozygous. |
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Describe the different patterns of inheritance and be familiar with examples
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AUTOSOMAL - gene in question is located on an autosome
SEX-LINKED - gene in question is locatied on sex chromosome. Autosomal recessive traits: - Sickle cell anaemia - heterozygotes unaffected - mating between 2 heterozygotes - 25% risk of affected child - 2 affected individuals- all offspring usually affected unless mutation has occured or recombination - males and females are at equal risk Autosomal dominant recessive - heterozygotes affected - very rarely found in homozygous states - affected person has 50% chance of transmitting the trait - males and females affected equally - every affected individual usaully has an affected parent Sex linked recessive inheritance - haemophilla A - x chromosome - hemizygous males ( only have 1 X chromosome) and homozygous females - Phenotypic expression more common in males as only one X chromosome - affected males transmit the gene to daughters but not to sons ( give them Y chromosome) - daughters of affected males are usually heterozygous - sons of heterozygous females have 50% chance of recieving recessive allele. |
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Explain dominance, recessiveness, co- dominance and complementation.
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Dominance - Phenotype expressed in heterozygotes.
Recessiveness - Phenotype only expressed in homozygotes of the allele. Co- dominance - Both alleles contribute to phenotype and so when both alleles occur together there is a blend of features or both features or presented eg blood group Isoglutamin (AB). Complementation: The relationship between 2 different strains of an organism which both have homozygous recessive mutations that produce the same phenotype. |
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How could you use genetic data to calculate probability of inheritance and recombination frequency.
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look at question 9 in book.
Linkage - If 2 genes are on different chromosomes they show independent assortment during meiosis. - Two genes that lie closely together on the same chromosome are linked and co-segregate ( inherited together) and so don't show independent assortment. Linked alleles can become seperated during crossing over resulting in recombination. The further away the genes are from each other on the chromosome, the more likely they are to be seperated by recombination. The recombination frequency is used to calculate the relative distance between the 2 genes. This is calculated by looking at offspring showing linked genetic traits and finding the percentage of offspring where the genes do not run together. A high percentage will show the genes are far apart. For example in ten offspring, if 1 recombinant progeny is produced then the recombination frequency is 1 in 10 ( 10%) and must be included when calculating inheritance probabilities. Recombination occurs in parent with both genes in question. |
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During which phases of mitosis are the chromosomes replicated.
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The chromosomes are replicated in S phase to form 2 sister chromatids which are genetically identical forming the chromosome. The chromosomes remain replicated through G2, prophase, metaphase but during anaphase the chromatids are seperated. They are no longer called chromatids, but chromosomes - the un-replicated form.
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If hearing loss is an autosommal recessive disease and 2 death people have 3 children, what proportional would be expected to be death. If it wasn't what you expected what could be the reason? write down the likely genotypes of parent and children.
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You would expect all 3 children to be death as both parents are homozygous for the mutant allele.
However if all children didn't suffer from hearing loss then this would suggest complementation, where more than one gene is involved in the phenotype and the genotype complements the other genotype. parents: A1A1, a2a2 and a1a1, A2A2 children all: A1a1, A2a2 - heterozygous for ear loss. 2 different strains with mutant homozyous allele produce the same phenotype, therefore breeding of 2 homozygous recessive mutant genomes would complement for the mutation and cause disease free individual |
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Describe the process and role of transcription.
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Role of translation is to produce an mRNA strand using DNA as a template. The mRNA strand is then used in translation to synthesise polypeptide chains.
1. Helicase breaks hydrogen bonds between DNA strands, exposing nucleotides. 2. Innitiation of transcription occurs when the promoter ( section of DNA upstream from ORF) is recognised by transcription innitiation factors eg c-myc which bind to it. RNA polymerase then binds to the promoter and moves along the template strand attaching complementary base pairs together in 5-> 3 direction elongation of new polynucleotide. Termination is sequence dependant and occurs when the sequence AAUAA is produced on mRNA. |
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Describe the process and role of translation.
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The role of translation is produce a polypeptide using mRNA template in the cytoplasm.
mRNA synthesised in the nucleus enters the cytoplasm via the nuclear pore. A ribosome attaches to the mRNA. The capped 5' end is recognised by methionyl tRNA and moves along strand until it find its complimentary codon to its anticodon. The codon, AUG is the innitiation codon and codes for the amino acid attached to the tRNA, methionine. Aminoacyl-tRNAs are all specific. The ribosome contains 2 aminoacyl-tRNA molecules in 2 sites, the p-site and the a-site. As the ribosome moves along the chain, the tRNAs form hydrogen bonds with their complimentary codons. The amino acid from p site tRNA moves the a site tRNA and forms a peptide bond with the amino acid catalysed by peptidyl transferase. The uncharged tRNA molecule then leaves the p-site in search for another specific amino acid. The a site amino acid moves to the p-site and a new aminoacyl tRNA attaches to the ribosome. Elongation of Polypeptide continues until a stop codon is reached which doesn't code for an amino acid eg UAA, UAG, UGA and termination of sequence is achieved.The polypeptide is assembled into a protein by forming secondary, tertiary and quaternary structure. The wobble pairing between anticodon and codon allows the tRNA to be attracted to many codons so that many codons can form the same amino acid. Therefore if there was a mutation on the wobble position, 3rd position this might not alter the amino acid. |
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Explain the wobble position.
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The wobble position is the 3rd position in a codon where normal specific base pairing rules don't apply. Therefore guanine can bond with cytosine and uracil. uracil can bind with adenine and guanine.
This allows more than one codon to code for the same amino acid and so there are 61 codons for amino acids ( 3 are stop codons) but only 50 tRNA molecules. |
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Describe a gene
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A unit of heredity. A length of DNA on the chromosome which codes for a protein as well as sequences necessary for its expression such as promoter and terminator sequences and introns.
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List and summarise the major reactions involved in the process of RNA maturation in eukaryotes and explain their importance in gene expression.
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The mRNA strand is unstable and vulnerable to degradation by exonucleases 3' and 5' in the cytoplams. Therfore in the cytoplasm, RNA processing occurs to mature mRNA.
1. Capping - guanine molecule is attached to 5' end of molecule, 5'-5'. - protects from degradation 2. Polyadenylation - 100s of adenines are added to mRNA to form a poly A tail - protects from degradation 3. Splicing - removal of introns (no functional value) using endonucleases |
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Describe the nature of the triplet code and be able to apply the genetic code.
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The triplet code comprises of 3 bases on the mRNA strand which code for a specific amino acid which is attached to a specific tRNA molecule. The anticodon on this tRNA molecule is complementary to the codon. It is a triplet code in order for all 20 amino acids to be coded for.
single code -> 4 amino acids double code -> 16 triple code -> 64 amino acids - way too many and so many codons code of the same amino acid as well as 3 stop codons. The genetic code is the universally recognised table linking 4 letter RNA bases to 20 letter amino acids. |
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Comprehend the implications of the degeneracy of the genetic code.
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Degenerat - more than one codon codes for an amino acid due to wobble pairing in 3rd position.
Degeneracy occurs as more codons are made than encodable amino acids. 20 codons for amino acids and 1 stop codon is needed however 64 codons are made. Wobble pairing allows degeneracy to occur as 3rd position base pairing isn't normal eg guanine can bind with uracil as well as cytosine. This allows silent mutations to occur if it is a base substituion in the 3rd position and the same amino acid is synthesised. |
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Contrast the different types of RNA molecules.
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mRNA
- makes up 2% of total RNA - RNA polymerase 3 - 100,000s types - few copies of each Reason mRNA is the copy of DNA and so contains all genetic material. There are so mnay variations of mRNA because many mRNAs can be made from the same gene depending on where the innitiation site and splicing occurs. tRNA - 15% of RNA - RNA polymerase 2 - 100 kinds - very many - needed for translation to take place rRNA - 80% of RNA - RNA polymerase 1 - few types - 5 - many copies - made in nucleolus - forms large subunits an small subunits of ribosomes. - not much variety as all ribosomes are very similar, however many copies are needed as they are required for translation. |
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Compare and contrast gene expression in mammalian and bacterial cells and explain how differences can be exploited clinically.
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mammalian cells don't have cell walls and so antibiotics such as penicillin whihc inhibit the synthesis of cell walls will destroy some bacterial cells but doesn't affect mammalian cells.
mammalian cells have different RNA polymerases than bacterial cells (think erthromyocin) and have different ribosomes 80S compared to 70 (50S and 30S)( rifampicin) Prokaryotes eg bacteria have no membrane bound organells, no introns, coupled transcription and translation, very unstable mRNA, 70s ribosomes, peptidoglycan cell wall. Eukaryotes eg humans, fungi, protozoa. - membrane bond organelles, many chromosomes, introns present, compartmentalised transciption and translation, mRNA stable (mature) and unstable( immature), 80S, No cell wall. Different ribosomes so enzymes destroying 30S and 50S subunits would only damage bacteria and not humans. |
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Predict the effects of various mutations in a gene.
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Mutations can be a single base substitution which if it occurs in 3rd position may be a silent mutation or may change an amino acid -missence mutation eg in sickle cell anaemia , A->T causes glutamate(-ve polar) -> valine (hydrophobic).
Nonsense mutuation - amino acid changed for a stop codon so truncated protein formed - reduced function. Single or non multiples of 3 base deletions and additions in the ORF can alter the reading frame causing a frame shift - and so all subsequent codons are different. 3 or multiple of 3 base deletion/addition doesn't affect the reading frame. triplet repeats - usually cause neurological problems - extended mRNA - might not be able to fit through nuclear pore tandum duplication - millions of bases added |
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Explain how mutations outside the coding region (ORF) can affect gene expression.
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Mutation upstream from the open reading frame might affect the promoter sequence. The transcription innitiation factors therefore might not bind to promoter and so RNA polymerase might not bind. Without RNA polymerase transcription can't occur in the gene is not expressed. A mutation in a splice site in an intron might cause alternative splicing and so a different mRNA is made.
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Cordcephin is another name for 3'-deoxyadenosine which is used for research purposes to inhibits the synthesis of mRNA. How may this work
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3'-deoxadenosine is an analogue of adenosine. It has 2'-OH and 3'-H.
Cordcephin can enter the cell because it lacks a negatively charged phosphate group, It becomes phosphorylated by kinases and can then act as a substrate for RNA polymerase because it has a 2' hydroxyl group unlike d. nucleotides. The analogue binds at 5' to neighbouring nucleotide but then prevents elongation as the formation of the next phosphodiester bond 3' can't happen due to lack of OH group. This compound could not disrupt DNA synthesis as DNA polymerise only recognises d. nucleotides which have a 2' H group and so it would not be used as a substrate. |
