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Biology
Term 1, 2014 - Genetics
| Question | Answer |
|---|---|
| What is DNA: What does it stand for? Where is it found? What is its significance? | DNA stands for deoxyribonucleic acid. It is a molecule found in the nucleus (and a little in the mitochondria) of the cells, and it contains all of the organism's hereditary information. |
| Describe the structure of DNA. | It is made of a phosphate and sugar (deoxyribose) backbone, and four nitrogen bases: adenine, thymine, guanine and cytosine. A & T form two hydrogen bonds. C & G form three. A & G are purines - double ringed. C & T are pyrimidines - single ringed. |
| Define nucleotide. | A group consisting of a phosphate, a sugar, and a base. |
| Define double helix. | A helix is a spiral. A double helix is two. |
| When are chromosomes visible in a cell? | During cell division, when DNA is compacted into chromosomes (prophase). |
| Describe the structure of chromosomes. | DNA condenses into a chromosome, and is replicated, resulting in two identical sister chromatids. They are made from chromatin (protein and DNA). During cell division, the sister chromatids are split. |
| What is a karyotype? | A karyotype is a chart that shows homologous chromosomes ordered by number and size. 22 pairs are autosomal. 1 pair are the sex chromosomes. The X chromosome is larger than the Y. |
| What was the conservative replication theory? (This was an incorrect theory) | Conservative replication would leave the 2 original template DNA strands together in a double helix and would produce a copy composed of two new strands containing all the new DNA base pairs. |
| What was the dispersive replication theory? (This was an incorrect theory) | Dispersive replication would produce two copies of the DNA, both containing distinct regions of DNA composed of either both original strands or both new strands. |
| What is the semiconservative theory? Why was it considered most reasonable? | Semiconservative replication would produce two copies that each contained one of the original strands and one new strand. It seemed most reasonable as it would allow each daughter strand to remain associated with its template strand. |
| How was the semiconservative replication theory proved? | It was confirmed by the Meselson-Stahl experiment, which allowed for autoradiographic visualization of the distribution of old and new strands within replicated chromosomes. |
| Describe the process of DNA replication: Step One. | Enzyme helicase unwinds the parental strands. Enzyme DNA Gyrase relieves the strain that this generates by cutting, winding, and rejoining the DNA strands. |
| Describe the process of DNA replication: Step Two. | DNA polymerase (& series of proteins) make complementary DNA strands w free nucleotides. On leading strand (5'-3') nucleotides are made continuously. On lagging strand (3'-5'), DNA fragments are replicated in Ozaki fragments later joined by DNA ligase. |
| Describe the process of DNA replication: Step Three. | DNA molecules rewind. Each new strand is coiled around histone proteins and further wrapped up to form separate chromatids joined by a common centromere. These chromosome has double the initial genetic information, to be split during cell division. |
| Describe protein synthesis: transcription. | 1)Enzyme RNA polymerase attaches to ‘promoter region’. 2)Elongation: transcription factors (proteins) unwind DNA (= single strand) 3)Termination: polymerase makes complementary mRNA. Terminator sequence = mRNA releases & polymerase detaches. |
| Describe protein synthesis: beginning. What is tRNA? | tRNA, or transfer RNA, begins its job once the mRNA and the ribosome are joined. tRNA is composed of an anticodon on one end, and a corresponding amino acid on the other. |
| Describe protein synthesis: translation. Elongation | During elongation (translation): tRNA brings amino acids according to the information provided by the mRNA. Amino acids are transferred, eventually forming a chain of peptide-bonded amino acids (polypeptide). |
| Describe protein synthesis: translation. Termination | During termination (translation): a stop codon is encountered, and the release factor terminates the translation. The ribosome dissociates, and the protein is freed. |
| Describe the protein synthesis: how does tRNA bring amino acids according to the transcription on the mRNA strand? (Part 1) | The mRNA strand’s first codon, typically AUG, binds with the appropriate anticodon. The amino acid for AUG, methionine, is fastened to the other end of the tRNA. |
| Describe protein synthesis: how does tRNA bring amino acids according to the transcription on the mRNA strand? (Part 2) | The second codon binds with its appropriate anticodon. Once this has been completed, the previous amino acid is transferred and linked to the new one. The previous tRNA is released, the ribosome moves along the mRNA strand, and the process repeats. |
| Define mitosis and describe its function. | Mitosis is the division of a diploid cell into two identical diploid cells. All somatic cells undergo mitosis for growth and repair. (And asexual reproduction for some organisms). |
| What is the acronym for mitosis? What does it mean? | IPMAT Interphase, prophase, metaphase, anaphase, telophase (and cytokinesis). |
| What are the phases of cell division? | Growth Phase 1 - rRNA, mRNA, tRNA produced in nucleolus Synthesis - interphase Growth Phase 2 - centrioles replicate, mitochondria/chloroplasts divide Meiosis - PMAT |
| Describe the process of mitosis: Interphase. | - DNA replicates |
| Describe the process of mitosis: Prophase. | - DNA condenses into chromosomes - Nuclear membrane and nucleolus break down - Centrioles migrate to opposite poles - Mitotic spindle fibres lay down - Aster forms (microtubules from spindles) |
| Describe the process of mitosis: Metaphase. | - Chromosomes line up at equator of cell - Spindle fibres attach to the chromosomes at the centromeres - Spindles constrict, causing chromatids to move slightly apart |
| Describe the process of mitosis: Anaphase. | - Centromeres split - Sister chromatids split and are pulled to opposite poles of the cell |
| Describe the process of mitosis: Telophase. | - Chromatids reach respective poles - New nuclear envelope forms around each group of chromatids - Spindle fibres disintegrate - Nucleolus reforms Cyotkinesis: - cleavage form (cells split) |
| Outline the stages of Meiosis I. (Interphase, prophase, metaphase) | Interphase - DNA replication Prophase 1 - Chromosomes & homologous pairs (synapsis) - Crossing over - Nuclear membrane/nucleolus break down - Centrioles migrate, spindles appear Metaphase 1 - Randomly line up - Slightly pulled apart |
| What is meiosis? | Meiosis is the division of a diploid cell to produce four non-identical haploid cells (gametes). |
| What is the significance of meiosis? | Since a) chromosomes 'cross over', i.e. exchange parts of genetic info to make new combos; b) line up in a random order, i.e. daughter cells aren't identical. Thus offspring is genetically different, increasing genetic variation/gene pool. |
| Define chromosome. | a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. |
| Outline the stages of Meiosis I. (Anaphase, telophase) | Anaphase 1 - Spindles contract - Homologous chromosomes separate (sister chromatids attached) Telophase 1 - Nuclear envelopes form around two new groups of chromosomes |
| Outline the stages of Meiosis II. | PMAT occurs, in the same way as mitosis. However, it occurs separately in the two cells formed form Meiosis One (these cells are still attached to each other though). |
| Define homologous. | Having the same relation or structure: in chromosomes, these are similar in structure, and contain alleles for the same genes in corresponding loci. |
| Define ova. | Plural of ovum, the mature female reproductive cell. It is haploid, produced by meiosis. |
| Define zygote. | A fertilized ovum, created from the fusion of two gametes. |
| Define fertilization. | The fusion of a male and female gamete to produce a zygote. |
| Define mutation. | The changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations. |
| Define monohybrid cross. | Hybridization using a single trait with two alleles (as in Mendel's experiments with garden peas. |
| Define hybrid. | The offspring of two plants or animals of different species or varieties, such as a mule. |
| Define locus. | The specific location of a gene. |
| Define pedigree. | The recorded ancestry or lineage of a person or family. |
| Define autosomal and sex linked traits and genes. | Autosomal: Traits/genes carried on the chromosomes other than the sex chromosomes. Sex-linked: Traits/genes carried on the sex chromosomes. |
| Name 4 types of mutations. | Point (single site on DNA) Deletion Insertion Translation (chunks of DNA moved) |
| What is the effect of the environment on phenotype? | Some characters are inherited from your parents' genes. Others are acquired from the environment, e.g. sun tans skin colour, nutrition affects growth. |
| What is Mendel's First Law of Segregation? | 'Each organism has two alleles for each trait.' |
| What is Mendlel's Second Law of Segregation? | 'The two alleles for a trait must separate when gametes are formed. A parent randomly passes only one allele from each trait to each offspring.' |
| What are alleles? | Different forms of the same gene, found at the same loci on homologous chromosomes. |
| Explain sex-linked inheritance. | Sex-linked inheritance occurs when traits are only carried on one of the sex chromosomes, e.g. on the X chromosome. This can affect the likelihood of being affected in terms of gender, e.g. more males affected by X-linked diseases. |
| Why are males more vulnerable to X-linked diseases? | If the trait was recessive, then females would need to inherit two recessive alleles to be affected - one X from each parent - which is quite rare; whereas males only need one recessive allele from their mother. |
| How can you tell a trait is dominant on a pedigree? | - It appears in every generation. - Anyone who has the trait, has a parent who has the trait. - May affect more people than not. |
| How can you tell a trait is recessive on a pedigree? | - It may not appear in every generation. - Unaffected parents may have affected children. - May affect less people than unaffected. |
| How can you tell a trait is sex-linked on a pedigree? | More males are affected. If not, the trait is autosomal. |
| What is convergent evolution? | A type of evolution that occurs when organisms come from different ancestral lineages. This creates analogous structures - different structures that perform the same function. e.g. bird and insect wings, shark and dolphin fins |
| What is divergent evolution? | Evolution resulting in species that were once similar/had the same evolutionary origin, but are now evolving separately. This results in homologous structures - they are similar in arrangement and function, but are becoming less alike. |
| What are vestigial structures? Where do they come from? | These are a result of divergent evolution. They are structures with little or no use to the organism; remnants that used to serve important functions. e.g. whale pelvis, ostrich wings, human coccyx. |
| Variations in traits may be due to: (two things) | Selection factors or mutations. |
| What is natural selection? Who came up with this theory? | Better adapted species are more likely to survive and pass on their genes. OR An organism with beneficial mutation could be more likely to survive and pass on their genes. - Charles Darwin |
| What are examples of selection pressures resulting in survival mechanisms within organisms? | Genetic Drift Bottle-neck Effect Founder Effect Parallel Evolution Geographical Isolation Behavioural Isolation Size of Population Natural Selection |
| Define 'genetic drift'. | A change in the frequency of alleles that pushes towards fixation. It occurs faster in small/isolated populations and slower in larger/non-isolated populations. |
| Give examples of natural selection. (Peppered Moth) | - initially more light moths - variation and competition - industrialization = dark trees - more dark moths * advantageous allele* *more likely to survive* |
| Define speciation. | When two populations isolated from each other evolve into two different species. |
| What are the six stages of Natural Selection? | 1)Variation 2)Competition 3)One of the alleles become advantageous (Struggle to Survive) 4)Individuals with ad. allele become more likely to survive(Survival of the Fittest) 5)Advantageous genes passed on 6)Change in allele distribution/gene pool |
| What is the difference between microevolution and macroevolution? | Micro - leads to subtle changes in phenotype e.g. sparrows smaller and lighter to survive in cold Macro - leads to speciation e.g. varieties of lemurs in Madagascar (geographic isolation) |
| Name four types of mutations. | Neutral(common) Deleterious (harmful) Lethal (fatal) Advantageous (beneficial) |
| Mutation acts in opposition to: | Genetic drift, by increasing variation. |
| Define adaptation. | When traits are changed to adapt to the environment. |
| Give examples of the effect of Natural Selection. | Fish has decreased in size, as smaller fish escape being caught more easily. Bacteria have adapted to antibiotics. |
| How have humans used Natural Selection to their advantage? | E.g. breeding crops; breed desirable traits and rule out others. This is artificial selection - interference of humankind. |
| What is the difference between sexual and asexual reproduction? | Asexual - one parent, less energy, faster, lots of offspring, less paternal care Sexual - two parents, more energy, slower, less offspring, more paternal care |
| List the advantages and disadvantages of asexual reproduction. | Ad. - no mate required, less energy, quicker, don't require as much paternal care Disad. - there is no genetic variability as offspring is identical to parent. This makes the species less likely to cope with an environment change. |
| What are the advantages of sexual reproduction? | Ad. - Higher change of survival due to genetic diversity by reproduction method, e.g. cross over, random line-up. Characters and abilities are different. Those with the best characteristics live on and produce offspring with the same characteristics. |
| List the types of sexual reproduction. | Internal fertilization, external fertilization. |
| List the types of asexual reproduction. | Binary fission (cell divides), budding (grows off parent), parthenogenesis (unfertilised egg forms individual), fragmentation/regeneration (small bit breaks off and becomes individual). |
| What is behavioral isolation? | Rituals and behaviors of a species that prevent interbreeding. |
| What is geographic isolation? | When two populations are located in different areas; geographically isolated. e.g. lemurs in Madagascar |
| What is the founder effect? | When a small proportion of a bigger population with a typical variation of genotypes moves to a new area. |
| Give examples of divergent evolution. | e.g. beaks of Darwin's finches e.g. forelimbs in humans, bats, and whales |
| What is the bottle-neck effect? | When an event e.g. natural disaster, mass extinction, causes a population to decrease in size, thus leaving a smaller population with a smaller gene pool, leading to an alteration of allele frequencies. |
Created by:
candyclouds
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