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Understanding Gene Mutations: Role in Evolution and Genetic Variation

Explore the role of gene mutations in evolution and genetic variation, including gene duplication, gene deletion, exon shuffling, and horizontal gene transfer. Discover how these genetic changes contribute to the diversity of life forms.

estherfreeman
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Understanding Gene Mutations: Role in Evolution and Genetic Variation

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  1. Questions

  2. 09_12_Mutation.jpg

  3. Gene Evolution Pages 293 - 319

  4. Learn… • How did your current genes get here… • The role of mutations on genes… • Transposons & evolution • The role of genes on evolution… • Phylogenetic studies

  5. Perspective on the human genome If we expand the distance between the bases to 1mm Then the human genome would extend 3200km - stretch across central Africa Every 300m = gene Every gene = 30m Coding region = 1m

  6. More perspectives on the human genome • Just about 2% of the entire genome is coding • About another 2% has a regulatory role • About 95% is ‘junk’ DNA! • Most mutations in the ‘junk’ DNA are neutral and free to accumulate without effect • 200 cell divisions from conception to gamete production • 6.4 billion bp of DNA • = 100 new differences in the DNA between parent and child sequences each generation

  7. Genetic variation • Nature has struck a good balance between maintaining the integrity of DNA replication allowing the functioning of the cell & the incorporation of genetic variation for evolution. • In evolution the germ cells are the important factor and not somatic cells

  8. 09_02_Germ_somatic2.jpg

  9. 5 types of genetic change • Gene Mutation • Gene Duplication • Gene Deletion • Exon Shuffling • Horizontal Gene Transfer

  10. Gene Mutation • Single base changes (point mutations) • Substitutions - swapping of one base for another - A to G • Point deletions - loss of one base • Point additions - addition of a base • E.coli maintains about 1 mistake in 10E9, and humans 1 in 10E10

  11. Gene Mutation… • Advantageous - gives a selective advantage and passed on to offspring • Selectively Neutral Mutations - no effect and is kept - also known as Silent Mutations • Deleterious - harmful and result in the death of the cell or individual, normally prior to reproduction

  12. Gene Duplications • Entire genes duplicated - by repetitive sequences on each side of the gene mis-pairing during replication

  13. 09_05_Gene.duplicate.jpg

  14. Gene Duplications • Entire genes duplicated - by repetitive sequences on each side of the gene mis-pairing during replication • Most important mechanism for generating new genes • Newly duplicated gene is free to diverge through more mutations - duplication and divergence • Gives rise to related gene families - opsin visual pigment genes & globin gene family

  15. Gene Duplications…Globins • < 500 million years ago - a single globin gene was responsible for carrying oxygen • 500 million years ago - a duplication took place in fish followed by divergence - leading to the genes for alpha and beta globin • Then came the alpha2:beta2 hemoglobin • In mammals the beta duplicated to give rise to epsilon chain - used in fetal hemoglobin

  16. Localized duplications • In genes such as for immunoglobulin proteins, each domain is coded for by an exon. • Duplication of exons leads to additional domains in the protein. • Since exons are flanked by long introns then misalignment of introns can introduce exon dulpications. • The 30,000 human genes are proposed to have arisen by duplication and shuffling of just a few thousand distinct exons.

  17. Transposons • Transposons are mobile DNA elements akin to plasmids in bacteria. They are present in large numbers (500,000 Alu-like transposons in human genome) • They are constantly moving around the genome • When two Alu-like transposons flank a gene they sometimes transpose the gene too to the new position.

  18. Horizontal transfer • Normal gene transfer through reproduction is termed VERTICAL GENE TRANSFER • Gene transfer across species is termed HORIZONTAL GENE TRANSFER • Very rare in Eukaryotes, but common in prokaryotes • Use of sex pilus to undergo conjugation • Important for Antibiotic resistance • Theory that the earliest cells exchanged genes via this method and then differentiated into the three divisions

  19. 09_13_conjugation.jpg

  20. Time & relationship • Comparison of critical gene sequences allows the determination of the evolutionary time. • Man and chimp had a common ancestor about 5 million years ago (mya) • Man and Gorilla about 8 mya • Man and Orangutan about 13 mya

  21. 09_15_Phylogen.trees.jpg

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