Natural selection and mechanisms of evolution pt 1

Going public 7 years have passed since the Beagles voyage 1844: Darwin gave his wife a 213 page manuscript outlining his theory Worried of public feedback, he didn’t go public By 1858 he had written 250,000 words!! 250, 000!! That same year he received a letter from a certain Alfred Russell Wallace, naturalist in Malaysia He had arrived at the same conclusions, independently of Darwin==uh oh Darwin 20 years vs. Wallace 2 days

Still going public Darwin submitted his paper along with Wallace’s at the next Linnaean Society meeting, July 1, 1858 A year and a half later, Darwin condensed his 250, 000 word behemoth into On the Origin of the Species.

Natural Selection Darwin’s words: “…can we doubt that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable traits and the rejection of injurious variations I call Natural Selection.”

Evolution by natural selection Observation 1 Individuals within a species vary in many ways Observation 2 Some of this variability can be inherited Observation 3 Every generation produces far more offspring than can survive and pass on their variations. Observation 4 Populations of species tend to remain stable in size Inference 1 Members of the same species compete with each other for survival Inference 2 Individuals with more favourable variations are more likely to survive and pass them on. Survival is not random. Inference 3 As these individuals contribute proportionately more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)

Opposition The publication of his book did not come without critical opposition Recall, evolution requires time==many people didn’t believe in the view that earth was many millions of years old Fossil record wasn’t as extensive during their time==many gaps Looking back at whales, today scientist have found 50-million year old whale fossils with fully functioning hips and hind limbs. They also have found 38-million year old ancestral whales that have tiny, non-functional hind limbs.

Environmental change Before the industrial revolution most trees in England were covered with a light coloured lichen This lichen provided good camouflage for light coloured peppered moths With the onset of the industrial revolution in the early 1800’s most plant life became covered in black soot By the late 1800’s most of the lichen was dead and everything became black==started to see a new black variety of the moth By 1920, almost all of the peppered moths were black Any guesses why?

Biggest "flaw" Darwin and Wallace’s theory failed to provide and explain where new variations came from The answer to this lie in the work of Mendel and his experiment testing inheritance within the pea plant Today new variation is attributed largely to genetic mutation and recombination Advances in genetics have provided further evidence for evolution and solved most of the evolutionary puzzle

Genetic Variation Geneticists study changes in the inheritable traits of organisms. Inheritable traits are represented by genes: these are portions of DNA (nucleic acid) that code for polypeptides (i.e. proteins and traits) Genes are located at specific points (loci) of the chromosomes Most eukaryotic organisms are diploid==2 sets of chromosomes; one from each parent

GV continued Genes can come in multiple forms called alleles An organism whose alleles are the same for a given trait is said by homozygous Conversely, if that organism has different alleles for that trait then they are heterozygous

More GV All individuals of a species possess the same genome: which is the complete set of chromosomes, genes and DNA, for that organism However each individual will have a different genotype, which is the set of all alleles possessed by the individual The phenotype, is the physical manifestation of the individual’s traits, based on the interaction between genes and the environment And these phenotypes are acted on by natural selection

Genomes With the advances in genomic technology such as DNA sequencing, scientists have the power to map genomes, analyzing and comparing genetic code Results? Amount of DNA varies from species to species The larger the genome the greater potential for genetic diversity==more mutation Many eukaryotic organisms such as humans have non-coding sequences in their DNA==introns The greater the number of alleles for a gene the greater the genetic diversity

Amount of DNA Species Common name DNA kilobases Estimated number of genes Mycoplasma genetalium bacterium 580 470 Saccharomyces cerevisiae yeast 1200 6500 Drosophila melanogaster fruit fly 180 000 13 000 Xenopus laevis toad 3 100 000 unknown Macaca nigra macaque 3 399 900 Homo sapiens human 3 400 000 42 000 Necturus maculosus mud puppy 81 300 000 Amphiuma means newt 84 000 000 Trillium species trillium 100 000 000 Amoeba dubia amoeba 670 000 000

Populations A population consists of all members of the same species living in the same region The amount of genetic diversity goes through the roof through sexual reproduction For example: an organism with 10, 000 genes is only heterozygous at 10% of the loci. This means that the organism could produce 2^1000 = 1.07150861 × 10301 This is more than the total number of atoms in the universe! (if you were curious this number is around 10^81) Needless to say, unless dealing with twins or clones, no two offspring will ever ever have the same genotype Note: this number is purely based on probability alone and doesn’t take mutation or crossing over into account

References Pgs 529-546 Review Q’s: Pg 516 #1, 6, 9 Pg 518 #3 Pg 528 #3, 4, 7, 8 Pg 546 #1, 3