Term
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Definition
| DNA has replicated; it is long, unravelled strands of chromatin. |
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Term
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Definition
| The chromosomes begin to shorten and fatten as the centrioles align at opposite ends of the cell. The nuclear membrane disappears and the chromatids are now held together by the centromere. |
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Term
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Definition
| Spindle fibres from the centrioles attach the spindle fibres to each pair of chromosomes and line them up along the centromere, preparing to be divided. |
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Term
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Definition
| The daughter chromosomes are pulled to each end of the cell. |
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Term
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Definition
| The daughter nuclei begin to form and the cell elongates in preparation to divide. |
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Term
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Definition
| The cell organelles divide and the cytoplasm seals off, so that the two cells become entirely separate of each other. |
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Term
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Definition
| Are made up by a sequence of triplets, sets of three bases. |
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Term
DNA Replication:
Amino acid |
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Definition
| The building blocks of proteins, these are each coded for by a gene, or three bases. |
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Term
DNA Replication:
Step One |
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Definition
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Term
DNA Replication:
Step Two |
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Definition
| DNA 'unzips', breaking the hydrogen bonds between bases. Loose nucleotides in the cytoplasm move to join up with the exposed bases. |
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Term
DNA Replication:
What is it called? |
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Definition
| Semi-conservative replication, because each daughter chromosome has 1/2 of the original DNA. |
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Term
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Definition
| The DNA for that gene unwinds. |
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Term
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Definition
| This phase is called 'transcription'. Nucleotides pair up with the exposed genes and form mRNA. Adenine pairs to uricil, cytosine to guanine. |
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Term
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Definition
| The DNA rewinds while the mRNA leaves the nucleus through the nuclear pore. |
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Term
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Definition
| In translation, mRNA binds to ribosome, which is decoded. It is read in triplets, referred to as 'codons'. |
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Term
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Definition
| tRNA brings the correct amino acid to the codon. As each mRNA codon is 'read' at the ribosome, the matching anticodon carried by the tRNA fits to it. |
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Term
Protein Synthesis:
Spot question; what does the mRNA always begin with, and so what three bases does tRNA always start with? |
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Definition
| mRNA always starts 'AUG', so the first anticodon (carried by the tRNA) always begins with 'UAC'. |
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Term
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Definition
| As the second anticodon fits into place, the first anticodon is free to go. When the third is in place the second can leave, and so on. When the mRNA reaches a 'stop' codon, this ends and produces a polypeptide chain. The completed protein is then released. |
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Term
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Definition
| An organic compound consisting of folded polypeptides which facilitates a biological function. |
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Term
Genetic variation:
What is genetic biodiversity? |
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Definition
| An expression of the range of all alleles present in a population. The greater the variation present, the more alleles evolution can act on to select for favourable traits. |
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Term
Genetic varition:
What are mutations? |
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Definition
| Mutations are a permanent change in the genetic material of an organism. Mutations are spontaneous and random, and are typically rare. |
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Term
Genetic varition:
What causes mutation? |
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Definition
| Exposal to environmental factors such as ionizing radiation and mutagens (such as formaldehyde). |
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Term
Genetic variation:
What are point mutations? |
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Definition
| Point mutations are mutations that occur within a gene. DNA bases may be inserted, deleted or substituted. |
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Term
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Definition
Chromosomes have shortened and thickened, becoming clearly visible as two chromatids held together by a centromere. The group of four chromatids is called a tetrad or bivalent.
During this step, crossing-over can occur. |
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Term
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Definition
| The chromosomes arrange themselves along the cell equator, with each member of a pair of homologous chromosomes oriented towards an opposite pole. Spindle fibres from the centrioles begin to pull the chromosomes apart. |
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Term
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Definition
| Any pair combination of chromosomes from each of the homologous pairs can move towards the cell poles here. As the homologous pairs separate, the cell membrane begins to close between them. |
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Term
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Definition
| Two new cells form, genetically uniquie because of the random assortment of alleles on the chromosomes that separated and from crossing over. |
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Term
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Definition
| Chromosomes may undergo a rest phase in which they unravel. Shortening and thickening again indicates the start of the second stage of divisions, prophase II. |
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Term
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Definition
| Again, the chromosomes line up along the centromere. Spindle fibres form. As in metaphase I, the positioning of the chromosomes is random. |
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Term
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Definition
| Chromatids separate and are pulled to the cell ends for the second time by the spindle fibres. The cell membranes constrict between them. |
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Term
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Definition
| Now there are four haploid daughter cells, each of differing genetic makeup. |
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Term
Genetic Change:
What is evolution? |
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Definition
| Evolution is the process by which new species of organisms gradually develop from earlier forms. The process occurs slowly and often because of a change in the organism's environment. |
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Term
Genetic Change:
How does evolution proceed? |
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Definition
| Evolution proceeds by changes in the frequency of alleles in the population as some alleles provide more benefit than others. |
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Term
Genetic Change:
What does evolution act on? |
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Definition
| Evolution acts on populations rather than organisms. |
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Term
Genetic Change:
What is natural selection? |
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Definition
| Natural selection is the process that allows evolution to take place. Populations produce more offspring than can be supported by the environmental resources; therefore there is competition between them. Individuals with the best adaptations will survive to reproduce and pass on their 'successful' alleles. The frequency of these alleles will then increase in the gene pool. Environmental factors act as selecting agents of successful phenotypes. |
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Term
Genetic Change:
What is migration? |
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Definition
| Migration is the movement of individuals from one population to another. It allows for gene flow between population. |
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Term
Genetic Change:
What is gene flow? |
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Definition
| The movement of individuals from one population to another, which allows for a change in the frequency of alleles in populations. |
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Term
Genetic Change:
What is emigration? |
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Definition
| The movement of organisms (and thus their alleles) out of a population, reducing the genetic biodiversity. |
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Term
Genetic Change:
What is immigration? |
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Definition
| The movement of alleles into the population, increasing the genetic biodiversity of that population. |
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Term
Genetic Change:
Genetic Drift |
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Definition
| This is the change in allele frequencies due to chance (not selection) and may involve the loss of alleles from the population. It is most likely to have an effect on a small population or on a population if it becomes small and grows again. |
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Term
Genetic Change:
Founder effect |
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Definition
| This effect refers to a small group of individuals that colonises a new isolated area such as an island. This means that not only is the group going to be vulnerable to genetic drift and will probably not be representative of the original population. |
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Term
Genetic Change:
Bottleneck effect |
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Definition
| Occurs when a population is suddenly reduced to a small size. This typically occurs because of a catastrophic event in the environment, removing individuals indescriminantly, or as a result of human action such as the destruction of habitat or the introduction of predators. |
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