BIOB 375 1st Edition Lecture 21 Outline of Last Lecture I. Changes in chromosome numbera. Aneuploidy Outline of Current Lecture II. Transposable elementsa. DNA transposonsb. DNA retrotransposonsCurrent LectureVariation arises by Transposable elements- Transposable elements are DNA sequences capable of moving- They are found in all organisms CC x cc = CcPurple cornel x yellow cornel = Both purple and yellow? – strange McClintock’s hypothesisGenotype Cc: no transportation Genotype Cc Ctc: transportation Genotype Ccc Ctc/Cc: mosaic (transportation during development) - Early transportation produces purple color and late transportation produces yellow color, making a mosaic type of cornel (variegated) Two mechanisms of transposition:1. Cut and paste: DNA transposons2. Copy and paste: DNA retrotransposons General characteristics of transposable elements:- Terminal inverted repeats (but not all TEs have them)Copy and paste: Retrotransposons- Increase the copy number after each transposition- Increases length of DNA- Changes codingLoss-of-function- When the transposable element effects the coding and a mutation occurs that removes an internal partEffects of transposons Mutagenic effectsMutagenic effects Loss of function, Gain of function, Chromosome rearrangement (deletion) New phenotype Effects on genome size1. DNA transposons Not increase genome sizes significantly2. DNA retrotransposons Increase genome size over timeWhat can cause variation?1. Asexually reproduced –a. Mutationi. Base substritutions/indelsii. Chromosome mutationsiii. Transposition of TEs2. Sexually reproduceda. Mutationi. Base substritutions/indelsii. Chromosome mutationsiii. Transposition of TEsb. Chromosome RearangmentWhy does a triploid (AAA) watermelon have no seeds?- Due to inviable gametesHow do seeds produced? Sexual reproduction- Viable gametes requiredGametes produced by
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