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51 Cards in this Set
- Front
- Back
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Why could measurements be unrepresentative? |
-sampling bias -chance |
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Sampling bias? |
Selection process may be used, investigators may intentionally/unwittingly be taking unrepresentative samples. |
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Chance? |
Even if sampling bias is avoided, individuals chosen may be by chance not be representative. (e.g. 50 plants elected might just happen to be 50 tallest plants in population) |
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How to eliminate sampling bias? |
Random sampling |
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How to eliminate effects of chance? |
Large sample size (smaller probability chance will affect results) Analysis of data collected (analyse data using statistical tests, to see to which extent chance affects results. Tests allow us to decide if variation observed due to chance or another cause) |
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2 main causes of variation? |
-genes -environment |
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Examples of genetic differences |
Mutations: sudden changes to genes/chromosomes may or may not be passed to offspring Meiosis: Nuclear division of gametes, mixes up genetic material before passing on to gametes (therefore all different) Fusion of gametes: Inherit characteristics from both parents during reproduction, so they are diff from parents. Also fusion of gametes is a random process contributes to genetic variation. |
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How can genetic variation in asexual reproducing organisms be increased? |
Only through mutation, through 3 methods in sexually reproducing organisms. |
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What can be causes of environmental influences? |
Climatic conditions: temp, rainfall and sunlight. soil conditions, pH food availability. |
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How should we treat conclusions about the cause of variation? |
tentatively, and with caution (hard to distinguish affects of genes from environment) |
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What are the 3 components of DNA? |
-deoxyribose sugar -phosphate group -organic base |
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Two groups of organic bases? |
Single-ring: cytosine and thymine Double-ring: adenine and guanine |
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How are the sugar and phosphate groups joined in DNA molecules? |
Condensation reaction |
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Who worked out structure of DNA 1953? |
James Watson and Francis Crick |
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Structure of DNA? |
Made of two strands of long nucleotides, joined by hydrogen bonds between complimentary bases. (Can be thought of as ladder, phosphate and sugar alternate to form uprights, bases form the rungs) |
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What are the base pairings and the number of bonds that form between them? |
C-G: three hydrogen bonds A-T: two hydrogen bonds |
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Why must complementary base pairings occur? |
Double ring structure molecules are longer, must bind to single ring structure molecules for rungs of DNA ladder to be the same length. |
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Adaptations of a DNA molecule |
-Stable, can pass from generation to generation without change -It is 2 separate strands joined by hydrogen bonds, allows them to separate during DNA replication and protein synthesis -Large molecule, carries a lot of genetic information -Because base pairs are within helical cylinder of deoxyribose-phosphate backbone, to an extent genetic info is protected from corruption by outside chemical and physical forces. |
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Why did scientists initially believe proteins were responsible for passing on genetic material? |
Chromosomes only visible during cell division, and they are made of DNA and proteins. To produce the extensive variety of cells and organisms exists the hereditary material needed to be diverse, therefore they believed that proteins were the likely candidate as they have more chemical diversity. (In addition proteins such as enzymes and antibodies show great specificity) |
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Why did scientists initially believe that DNA was not the hereditary material? |
They believed DNA had too few components to fulfill the role. |
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How do scientists work to acquire evidence? |
Use observations and current knowledge to form a hypothesis, from this they make predictions about the outcome of an investigation. They carry it out a number of times, and collect experimental evidence that enables them to accept or reject hypothesis. |
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Scientific observations revealing DNA is hereditary material. |
Present in chromosomes in the right amounts, very stable quantity halved in egg and sperm cells but no other body cells. However this circumstantial evidence and not enough to prove cause an effect. |
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Experiment proving DNA is hereditary material |
Involved mice and a bacterium causing pneumonia. bacterium exists in 2 forms: -safe form (doesn't cause pneumonia) R-strain -harmful form (causing pneumonia) S-strain. Mice separately injected with living safe form or dead harmful form. When group injected with living safe form they remained healthy, so did group injected with dead harmful form. However when injected with both forms, they expected a similar result but the mice developed pneumonia. |
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DNA structure pneumonia experiment result |
Explanations include: -experimental error: not all harmful forms were killed -living safe form, mutated into harmful form (unlikely as exp, carried out numerous times with same result) -Pneumonia caused by toxin, harmful form has info to make toxin but cant because its dead. safe has means to make toxin, but not the info. Info may have been transferred from harmful to safe, which then produced it. - |
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Experiment carried out to explain 3rd explanation |
-Living harmful bacteria in mouse collected -Various substances in bacteria isolated and purified -Each substance added to suspensions of living safe bacteria, to see whether it would transform them into harmful form -Only substance that produced this transformation was purified DNA -When enzyme that breaks down DNA added ability to carry out this transformation ceased. Other x to support: Virus infect bacteria causing them to produce more viruses. Viruses made of just DNA and protein, one of them must possess instructions for bacteria to produce viruses. |
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What is gene? |
Sections of DNA, contain coded info for making polypeptides. Coded info in the form of specific sequences of bases along DNA molecule. Polypeptides combine to make proteins, so genes determine proteins of an organism. |
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When are chromosomes visible? |
When a cell is dividing |
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How many chromosomes do humans have? |
46 |
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How is DNA packed into chromosome? |
DNA is a double helix, helix is wound around proteins to fit it into position. This DNA-protein complex is then coiled, before being packed into chromosome. In this way lots of DNA condensed into 1 chromosome. |
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Why is there always an equal number of chromosomes in adult cells? |
Because they occur in homologous pairs. |
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Homologous chromosomes |
In humans each parent contributes a set of chromosomes to the offspring, so one of each pair is derived from chromosomes from each parent, these are known as homologous pairs and the total number is the diploid number. A homologous pair is always 2 chromosomes that determine the same genetic characteristic. |
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What is an allele? |
Different forms of a gene. |
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What are the results of a difference in the base sequence of a gene? |
Differences of an allele of a gene, may result in diff amino acid being coded for. Diff amino acid sequence may result in, production of diff polypeptide and a diff protein. Sometimes this diff protein will not function properly or will not function at all. When the protein produced is an enzyme, it may have diff shape so will not fit enzyme substrate, not able to carry out function can have serious consequences for organism. |
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2 ways the division of the nucleus of cells occurs?
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Mitosis: 2 daughter nuclei produced with same number of chromosomes as parent cell and each other. Meiosis: Produces 4 daughter cells with half the number of chromosomes as parent cell. |
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Why is meiosis necessary? |
During reproduction 2 gametes fuse together, to produce new offspring. If each gamete has diploid number of chromosomes, new cell would have 92, this doubling would occur with every generation, so to maintain a constant number of chromosomes in adults of a species, number needs to be halved at some point during the life cycle. Each cell produced in meiosis has haploid number of chromosomes. |
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How does meiosis produce genetic variation? |
-independent segregation of homologous chromosomes -recombination of homologous chromosomes by crossing over |
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Process of meiosis (simple) |
1st division: chromosomes pair up, chromatids wrap around may be exchanged through crossing over. 2nd division: chromatids move apart, 4 cells formed (each contains 23 chromosomes) |
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What is a gene? locus? |
G: section of DNA that codes for particular polypeptide L: position of gene on chromosome of DNA molecule |
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Independent segregation of homologous chromosomes |
-Chromosomes randomly line up next to homologous partner -One of each pair passed to daughter cell -Pairs lined up randomly, combination of chromosomes in daughter cells s random too |
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Crossing over |
-Chromatids line up next to partner -chromatids of each pair, wrap around each other -Tensions created and portions of chromatid break off -Broken portions rejoin with chromatids of its homologous partner -Usually equivalent portions of chromatids exchanged -So new genetic combinations are produce |
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3 situations that limit genetic diversity? |
-selective breeding -founder effect -genetic bottlenecking |
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Selective breeding/artificial selection? |
Individuals with desired characteristics selected, and they are used to parent next generation |
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How does selective breeding affect genetic diversity? |
Variety of alleles deliberately restricted to small number of desired alleles. Over many generations, leads to a population that only possesses desired characteristics but has reduced genetic diversity. |
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Why is selective breeding carried out? |
To produce high breeding yields of domesticated animals and plants |
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What is the founder effect? |
Few individuals from a population colonise a new region, only carry small fraction of the alleles from the whole population. The new population that develops from the few colonisers will show less genetic diversity than the population they came from. |
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Genetic bottleneck |
Population may suffer from dramatic drop in numbers. Sometimes caused by chance event such as volcanic eruption, not reproducing interference by man. Survivors possess smaller variety of alleles than original population, therefore less genetic diversity. As these few individuals breed and become reestablished , genetic diversity of new population will remain restricted. |
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Ethics of selective breeding |
-Scientific research requires funding, who funds the research may influence its outcome -Does it interfere with nature? Do other species have rights, should a new variety of species develop naturally -Which features should be selected and who decides? -How do we balanced increased yield with animal welfare? -Producing genetically uniform livestock, reduces genetic diversity. Could we be losing alleles that could be beneficial in the future? -Should we select animals that produce less methane, in the interests of global warming -Driven too much by consumerism? Should we stop trying to hard to produce higher yield varieties, and just pay more for our food? Is this fair to poorest in society? -Should we stop methods of sb because they are artificial, is it acceptable alternative to required characteristics by genetic enginering |
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Selective breeding cattle |
Artificial insemination of cattle (sperm of one bull used to inseminate 100s of cows). Selctively bred for 2 reasons: for meat and milk. |
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Effects of selectivly breeding cattle |
-genetic diversity reduced -doubling milk yield, reducing animal welfare -natural life span of cow is 25 years, most slaughtered after 5 years -calves suckle for 6-12 months normally, now 1-2 days so milk can be used by humans -from age 2 dairy cows continuously produce calves, and hence milk throughout their lives |
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Haemoglobin structure? |
primary: 4 polypeptide chains secondary: each polypeptide chain coiled into a helix tertiary: each pp chain folded into precise shape (important for its oxygen carrying role) quaternary: all 4 polypeptides linked to form spherical molecule. Each polypeptide associated with haem group, which contains a ferrous ion, each ferrous ion can bind with a singular oxygen molecule, so a total of 4 O2 molecules can be carried by a haemoglobin molecule in humans. |
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Role of haemoglobin? |
Transport O2. To do so effectively must, readily associate with oxygen at the surface where gas exchange takes place. Readily dissociate from oxygen at the tissues requiring it. |
