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Chapter 10 - Nature of the Gene and Genome (Spring 2011)

And lines non repeated dna sequences code for the

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Unformatted text preview: DNA sequences code for the majority of proteins The Stability of the Genome o o o o o o o o o Genomes can change rapidly in a few ways Whole Genome Duplication (Polyploidization): occurs when offspring receive more than 2 sets of chromosomes from their parents could be the result of hybrids from closely related parents, or could result from duplicate chromosomes not separated in embryonic cells Duplication and Modification of DNA Sequences: gene duplication occurs within a portion of a single chromosome may occur by unequal crossing over between misaligned homologous chromosomes Duplication has played a major role in the evolution of multigene families extra copy acts as raw material for evolution as sometimes accumulates and has a beneficial effect on the organism Evolution of Globin Genes: the globin gene family includes haemoglobin, myoglobin and plant lechemoglobin ancestral forms have given rise to recent forms by duplication, gene fusion and divergence Some sequences, called pseudogenes, resemble goblin genes but are not functional Jumping Genes: genetic elements are capable of moving within a chromosome (transposition) called transposable elements Transposition: only certain sequences can act as transposons, but these insert into target sites randomly requires the enzyme transposase to facilitate insertion of transposons into target site; bacterial transposition occurs by replication of the transposable element followed by insertion (transposase binds to donor DNA, cleaves off transposon, and inserts it in target DNA) Integration of the element creates a small duplication in target DNA, which serves as a footpring to indentify sites occupied by transposable elements 4 o o o o Retrotransposons: use an RNA intermediate which produces complementary DNA via reverse transcriptase; viruses such as HIV use this mechanism to replicate their genome Transposable elements can play evolutionary roles: transposable elements can carry parts of the host genome with them as they move, can bring together unlinked segments of the genome evolution of proteins that are composed of domains from different ancestral genes Transposable elements can regulate gene expression there are many transposable elements found in many transcription factors Transposable elements play a role in production of new genes, example: RAG in rearrangement of antibody genes Sequencing Genomes o o o o o o The genomes of hundreds of organisms have been sequenced In 2004 the finished vers...
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