Modern Theory of Evolution

1. Modern Theory of Evolution SBI3U0

2. The Age of Earth • The age of the Earth, and our solar system, has been confirmed to be approx. 4.5 billion years old • This matches well with Lyell’s geological theories • This age has been verified through several sources, one of which is through the use of radiometric dating • The use of the decay of radioisotopes

3. Radiometric Dating • Many atoms are stable and do not change over time • But certain atoms are unstable and undergo radioactive decay • Radioactive decay means that the nucleus of the atoms releases subatomic particles (or high energy light) to become more stable • This often changes the atom from one element to another

4. Radiometric Dating • Eg: Two of the main isotopes of carbon on Earth are C-12 and C-14 • C-12 has 6P and 6N, while C-14 has 6P and 8N • C-14 is unstable and breaks down into N-14 on a regular basis 14C  14N + e-1 • This decay occurs at a predictable pace • We define a “half-life” as the time it takes for half of the radioactive isotopes in a sample to decay

5. Half-life

6. Radiometric Dating • The proportion of a radioisotope in a fossil or rock can be compared to the amount in a living organism to determine how old the fossil/rock is • This method works for any radioisotope • They all have different half-lives • Eg: C-14 half-life = 5715 years No-253 = 102 seconds U-236 = 23,420,000 years K-40 = 1, 277, 000, 000 years

7. Plate Tectonics • The study of the Earth’s crust provides more evidence for evolution • The Earth’s crust is made up of several plates that shift relative to one another • This shifting creates mountains • It also moves continents relative to one another (very slowly)

8. Plate Tectonics

9. Plate Tectonics • If the motion of the plates is reversed (to look back in time), there was a time where the continents were all together • This super-continent was called Pangaea Pangaea broke up approx. 200 Million years ago

10. Plate Tectonics • Pangaea explains to locations of several fossils • Eg: Lystrosaurus (a triassic period land reptile) fossils are only found in Africa, India, and Antarctica • These land masses are adjoining in Pangaea

11. Modern Evolutionary Synthesis • Now that we know more about genetics and how traits are passed down, we have slightly redefined evolution • DNA, genes, alleles, meiosis, etc... • Evolution is defined as “a change in the gene pool of a species over time” • Gene pool: all of the alleles in a population at a given time • This means that evolution occurs when new alleles are formed, but also when the prevalence of one allele over another changes

12. Mutations • Changes to the gene pool are often due to mutations • Changes in the DNA sequence • Substitution, deletion, addition, inversion • Mutations can be either harmful, beneficial, or neutral

13. Mutations • Beneficial mutations • Convey an advantage to the organism and become selected for via natural selection • These mutations become more prevalent in the gene pool over time • Neutral mutations • Convey no advantage or disadvantage, but often become prevalent in the gene pool • Harmful mutations • Convey a disadvantage for survival/reproduction • These mutations either kill the organism outright, or do not become prevalent in the gene pool

14. Mutation • Mutations occur very rarely • Possibly once for every 1 million nucleotides that are copied • But with such a large population, and a large genome, the chance for mutations to create genetic variation is large

15. Homologous Genes • Organisms that are related have genes that code for the same things • Eg: mice and pigs are both mammals and thus have genes that code for the creation of fur, teeth, blood vessels, organs, etc... • These genes are called homologous because they are literally the same • Or at least similar due to mutations

16. Homologous Genes • Organisms that are closely related (in evolutionary terms) should have fewer mutations in their homologous genes than those that are more distantly related • And this is what we observe Cow CTATGGTTCC TAAGC ACAAG Deer CTATGGTTCC TAAGC ACGAA Whale CTATC CTTCC TAAGC ATAAA Hippo CTATC CTTCC TAAGC ATAAA Pig CCATTGTTCC CAAGC GTAAA Rat CCATC TTTCC TAAGC TCAAA

17. Pseudogenes • Species also have inactive genes called pseudogenes • These are genes that serve no purpose in the organism • Pseudogenes are very similar to vestigial features • They used to serve a purpose in an ancestral species, but have ceased to be important • Mutations caused damage to the gene to force it to stop functioning • Since the gene was not important for the organism, the mutations went unnoticed and gets passed along to offspring

18. Pseudogenes • Examples: • Humans and other primates, bats, guinea pigs, and some birds have a defective gene for vitamin K production • This gene is unnecessary due to the prevalence of vitamin K in the diet of these organisms • Mammals have approx. 1000 genes coding for the functioning of olfactory receptors (sense of smell) • Dolphins have no need for a sense of smell but still have these genes. • Only ~200 are functioning in dolphins, the rest are pseudogenes

19. Homework • Pg 313 #1-9