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34 Cards in this Set
- Front
- Back
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prokaryotic vs eukaryotic cells |
Prokaryotic: lack a nuclear membrane, don't have membrane bound organelles Eukaryotic: more complex, have a nucleus and membrane bound organelles such as chloroplast and mitochondria |
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alleles |
genes that specify a characteristic |
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are traits inherited? |
Traits are no inherited directly. genes are inherited and along with environmental factors determine the expression of a trait |
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genotype |
the genetic information that an individual organism posses (information in OCA2 genes that cause albinism is a genotype) |
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phenotype |
the trait an individual organism posseses (i.e almibinism) |
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genetic information is encoded in the molecular structure of nucleic acids which come in two types ... |
DNA and RNA |
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Mitosis |
The separation of chromosomes in the division of somatic (non sex) cells |
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Meiosis |
The pairing and separation of chromosomes in the division of sex cells to produce gametes (reproductive cells) |
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Evolution can be viewed as a two step process |
1. genetic variation arises 2. some gentic variants increase in frequency where as other variants decrease in frequency |
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What DNA strand do we usually write down? |
The non template strand because it will be the same as the sequence of RNA transcribed from the template strand (but it's U instead of T) |
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Transposable elements |
DNA sequences that can move about in the genome and they often cause mutations |
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Where are transposable elements found? |
Found in genomes of all organisms (both prokaryotes and eukaryotes) |
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What can transposable elements do? How do they cause mutations? |
- can insert themselves in different locations in the genome - through their movement (transposition) they cause mutations by inserting into a gene and disrupting it or by promoting chromosome rearrangements such as deletions, inversions and duplications |
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General characteristics of transposable elements |
- can be simple or complex - Short flanking direct repeats from 3 to 12 bp long are present on both sides of most transposable elements - these repeats are NOT part of the transposable element and do not travel with it but they yare generate in the process of transposition at the point of insertion - flanking direct repeats are created when staggered cuts are made in the target DNA - These staggared cuts leave single stranded pieces of DNA on either side of the transposable element- replication of these single stranded pieces creates the flanking repeats |
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flanking direct repeats |
- Short flanking direct repeats from 3 to 12 bp long are present on both sides of most transposable elements (sequences of these repeats vary but their length is constant for each type of transposable element)- these repeats are NOT part of the transposable element and do not travel with it but they yare generate in the process of transposition at the point of insertion - flanking direct repeats are created when staggered cuts are made in the target DNA - These staggared cuts leave single stranded pieces of DNA on either side of the transposable element - replication of these single stranded pieces creates the flanking repeats |
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When are flanking direct repeats created? |
- flanking direct repeats are created when staggered cuts are made in the target DNA - These staggared cuts leave single stranded pieces of DNA on either side of the transposable element - replication of these single stranded pieces creates the flanking repeats |
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terminal inverted repeats |
- found at the end of many transposable elements - They are sequences from 9 to 40bp in length that are inverted complements of each other - Terminal inverted repeats are recognized by enzymes that catalyze transposition and they are required for transposition to take place |
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Transposition |
the movement of a transposable element from one location to another |
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transposase enzyme |
the transposable element often codes for this enzyme, it's used to make the staggered breaks in the DNA and to integrate the transposable element into a new site |
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DNA transposons |
some transposable elements that transpose as DNA |
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Retrotransposons |
Transpose through an RNA intermediate - RNA is transcribed from the transposable elelent (DNA) and is then copied back into DNA by an enzyme called reverse transcriptase |
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Are the transposable elements found in bacteria tretrotransposons or DNA transposons? |
DNA transposons |
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Are the transposable elements found in eukaryotes tretrotransposons or DNA transposons? |
Both DNA transposons and retrotransposons are found in eukaryotes but retrotransposons are more common |
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among DNA transposons transposition can be one of two types? |
Replicative transposition non replicative transposition |
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Replicative transposition |
Type of transposition amoung DNA transposons and retrotransposons - also known as copy and paste transposition - Replicative transposition: a new copy of the transposable element is introduced at a new site while the old copy remains behind at the original site so the number of copies of the transposable element increases as a result of transposition |
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Non replicative transposition |
Type of transposition among DNA transposons - Non replicative transposition: the transposable element is excised from the old site and inserted at the new site without an increase in the number of copies |
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How do organisms limit transposition? |
- By methylating the DNA in regions where transposons are common - Methylation usually suppresses transcription preventing the production of the transpose enzyme which is necessary for transposition - in other cases translation of the transpose mRNA is controlled - some animals use small RNA molecules called Piwi-interacting RNA's (piRNA's) to silence transposons (piRNAS combine with Piwi proteins to inhibit the expression of transposon sequences) |
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What has been discovered in regards to transposition in humans? |
People differ in the number and location of their transposons |
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What can be said about cancer cells and transposition? |
some cancer cells have elevated levels of tranposition probably because cancer cells do not respond to the DNA methylation |
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can transposition be beneficial |
transposition is generally mutagenic but occasionally they may be beneficial (i.e bacterial transposable elements sometimes carry genes that encode antibiotic resistance) |
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why does transposition lead to DNA rearangements? |
Because transposition requires the exchange of DNA sequences and recombination. homologous recombination between multiple copies of transposons can lead to duplications, deletions and inversions |
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In nonreplicative transposition what can be cause by the excision of transposable elements? |
DNA rearrangements,if the DNA broken is not repaired properly DNA rearrangements can be generated |
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How do we know that many transposable elements sevre no purpose for the cell and they exist simply because they are capable of replicating and spreading? What can we think of transposable elements as? |
Because of their ability to replicate and spread (i.e replicative transposition) Transposable elements can be taught of as gnomic parasites that provide no benefit to the cell and can even be harmful. |
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domesticated transposons |
transposable elements that have evolved to serve a useful purpose for their host cells so their parasitic tendencies have been replaced by properties useful to the cell |
