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65 Cards in this Set
- Front
- Back
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What is a Gene? |
A length of DNA that codes for a polypeptide. |
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What is the Genetic Code? |
A triplet code which is degenerate so all amino acids except methionine have more than one code. Some are "start" and "stop" genes. It is widespread but not universal. |
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Describe the process of transcription. |
RNA polymerase attaches to the double helix breaking hydrogen bonds and so the DNA uncoils. RNA polymerase lines up free RNA nucleotide bases by complementary base pairing. Hydrogen bonds form between bases. RNA polymerase detaches when it reaches a stop codon. The mRNA leaves the nucleus and attaches to a ribosome. |
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Describe the process of Translation. |
tRNA carries amino acids to the ribosome. A tRNA molecule with a complementary anticodon attaches to the mRNA. A second tRNA molecule attaches in the same way. The two amino acids attached to tRNA are joined by a peptide bond and the first tRNA molecule moves away. This is continued until there is a stop codon. |
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What are the different types of mutation? |
Subsitution, Deletion, Insertion, Duplication, Inversion. |
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Why can some mutations have a neutral effect? |
1) The mutation changes a base in a triplet, but the amino acid coded for doesn't change due to the genetic code being degenerate so coded by more than one triplet. 2) The mutation produces a different amino acid but it is chemically similar to the original. 3) The mutated amino acid is not involved in protein function. |
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How do some mutations have a beneficial effect? |
They increase an organim's chances of survival. eg. Antibiotic resistance in bacteria. |
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How do some mutations have a harmful effect? |
They decrease chances of survival. eg. Cystic fibrosis. |
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Outline protein activation involving Cyclic AMP. |
PKA is an enzyme made of four subunits. When cAMP isn't bound the four units are inactive. The binding of cAMP causes a change in the enzyme's 3D structure, releasing the active subunits. |
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What is the function of B-galactosidase? |
It catalyses the hydrolysis of lactose to glucose and galactose. |
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What is the function of Lactose permease? |
It transports lactose into the cell. |
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What is the function of the operator region? |
It switches genes on and off. |
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What is the function of the promoter region? |
It is where RNA polymerase binds to in order to begin the transcription of structural genes. |
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What is the function of the regulator gene? |
It codes for the repressor protein. |
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Decribe activities of the lac operon when lactose is absent. |
The regulator gene produces the lac repressor which binds to the operator region and blocks the promoter region where RNA polymerase normally attaches. So RNA polymerase cannot bind and structural genes cannot be produced. |
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Describe activities of the lac operon when lactose is present. |
Lactose binds to the repressor, changing its shape so that it cannot bind to the operator site. RNA polymerase binds to the promoter region, thus starting the production of enzymes. |
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What are homeobox genes? |
Genes which code for the development of body plans. Homeotic genes have regions called homeobox sequences that code for the homeodomain. This binds to DNA at the start of developmental genes, activating or repressing transcription and so altering the production of proteins involved in body plan development. |
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What is apoptosis? |
Programmed cell death. The cell produced enzymes which break down important components such as proteins in the cytoplasm and DNA. The cell begins to shrink and break into fragments. The fragments are engulfed by Phagocytes. |
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What are the uses of apoptosis? |
Development of hands and feet. Tadpole development. Nerve cells that are not needed. |
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Describe Prophase 1. |
DNA condenses, the nucleoli and nuclear evelope dispear. The spindle starts to form Chromosomes become visible as tetrads. |
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Describe Metaphase 1. |
Tetrads line up at the equator, the spindle has completely formed. Independent assortment occurs. |
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Describe Anaphase 1. |
Tetrads pull apart and chromosomes with two chromatids move towards the poles. |
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Describe Telophase 1. |
Chromatids decondense and the nuclear envelope reforms. Each daughter cell is haploid. Cytokinesis follows. |
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Describe Prophase 2. |
Chromosomes become visible as they condense. |
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Describe Metaphase 2. |
Chromosomes line up and the equator. Crossing over occurs. |
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Describe Anaphase 2. |
Chromosomes split, so that a chromosome with only on chromosome heads towards each pole. |
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Describe Telophase 2. |
Chromosomes with only one chromatid decondense and are surrounded by a new nuclear envelope. The four daughter cells are haploid. Cytokinesis follows. |
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What is Crossing over? |
Non-sister chromatids twist around eachother and bits of the chromatids swap over. Therefore the chromatids have a different combination of alleles. |
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What is independent assortment? |
Occurs during Metaphase I and II. Different combinations of maternal and paternal chromosomes go into each cell. So each cell ends up with a different combination of of alleles. |
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What is an allele? |
A different version of a gene.The order of bases is different so it codes for a different version of a characteristic. |
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What is a locus? |
The fixed position of a gene on a chromosome. |
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What is a phenotype? |
The physical expression of the genotype. |
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What is a genotype? |
The alleles an organism has. |
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What is a dominant allele? |
An alleles whose characteristic is expressed even if there is only one allele present. |
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What is a recessive allele? |
An allele whose characteristic only appears in the phenotype when two copies are present. |
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What is codominance? |
When both alleles are expressed in the phenotype. Ratio 1:2:1 |
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What is Sex linkage? |
The Y chromosome is smaller so therefore contains fewer genes, so most genes are carried on the X chromosome. Because males only have on copy of some genes, its characteristic is always expressed and they are more likely to show recessive characteristics. |
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What is epistasis? |
An epistatic gene masks the expression of another as many genes can control the same characteristic. |
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What is recessive epsitasis? |
When having two copies of the epstatic allele masks the expression of the other gene. Ratio 9:3:4 |
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What is dominant epistasis? |
When having at least one copt of the episatic allele masks the expression of the other gene. Ratio- 12:3:1 |
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What is the null hypothesis? |
It means there is no significant difference. |
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Describe the Chi Squared test. |
Work out the column row and overall totals. Calculate expected frequencies (row x column) divided by overall. For each category work out (O-E) squared divided by E. Add up the values. Work out degrees of freedom (rows-1)(columns-1). Look up the significance level, if the value is bigger reject and smaller accept. |
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What is variation? |
The differences that exist between individuals. |
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What is continuous variation? |
When indiviuals within a population vary within a range. There are no distinct categories. It is quantitative and polygenic. |
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What is discontinuous variation? |
When there are two or mor distinct categories and no intermediates. It is qualitative and monogenic. |
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How do genes cause variation? |
Individuals of the same species have the same genes but diffferent alleles, resulting in different genotypes and therefore different phenotypes. |
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How does the environment cause variation? |
Climate, food, lifestyle influence phenotype. |
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How do both genes and the environment cause variation? |
Genetic factors determine the genotype an organism is born with but environmental factors can influence how some characteristices develop. |
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What is evolution? |
The change in frequency of alleles in a population over time. |
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What is stabilising selection? |
When the environment isn't changing, individuals with alleles towards the middle of the range are more likely to survive and reproduce. It reduced the range of possible phenotypes. |
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What is directional selection? |
When there is a change in the evironment, individuals with alleles for characteristics of an extreme type are more likely to surviv to reproduce. |
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What is genetic drift? |
Individuals within a population show variation. By chance, the allele for one genotype is passed onto offspring more often than others. If this happens again, it can lead to evolution as the alleles become more common. It usually has a greater effect on smaller populations and if there is a genetic bottleneck- a population becomes smaller due to a natural disaster. |
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What are the conditions of the Hardy-Weinberg principle? |
Large population no immigration or emigration no mutation random mating |
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How is allele frequency prediced? |
p + q= 1 p= frequency of dominant allele q= frequency of recessive allele |
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How is genotype frequency predicted? |
p2 + 2pq + q2= 1 P squared= homozygous dominant Q squared= heterozygous dominant 2pq= homozygous recessive. |
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Describe the process of natural selection? |
There is variation within a population. Predation, disease and competition create selection pressure. Individuals that have an allele which increases chance of survival are more likely to survive, reproduce an pass on the allele. Therefore a greater proportion of the next generation will inherit the beneficial allele and its frequency increases. |
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Describe the process of artifical selection? |
Individuals eith the most desirable traits are isolateed and bred together. The offspring with the most desirable traits are selected and bred together. This is continued over several generations. |
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What are the similarities between natural and artificial selection? |
Both change the allele frequencies in the next generation. Both make use of random mutations. |
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What are the differences between natural and artificial selection? |
Natural selection= environment Artificial selection= humans Artificial selection aims for a predetermined result. Artificial selection makes the species more useful to humans. |
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What is speciation? |
The development of a new species. |
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What is geographical isolation? |
A physical barrier divides a population of species. Conditions on each side will be different, so different characteristics will become more due to their being different selection pressures. Eventually the two populations will not be able to breed together to produce fertile offspring. |
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What is reproductive isolation? |
Seasonal changes Mechanical changes Behavioural changes |
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What are the problems with the biological species concept? |
They might be extinct They might reproduce asexually They might be practical or ethical reasons involved. |
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What is the phylogenetic species concept? |
The study of evolutionary history, and how closely related species are. |
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What are the problems with the hylogenetic species concept? |
There's no cut off to say how different two organisms have to be different species. |
