Bio lec 13

create detailed summary

Okay, I can provide a detailed summary of the concepts presented in the source material, drawing on the information provided.

The source begins with information about the Mayapple (Podophyllum peltatum), a woodland plant found in eastern North America. It grows in colonies and all parts except the fruit contain a toxin called Podophyllotoxin, which has been used to create medications for viral infections. The fruit is edible, said to taste like pineapple, and is eaten by various animals.

The core of the sources discusses the theory of Evolution by Natural Selection, developed by Charles Darwin. Darwin's path to natural history involved initial studies in medicine and theology, which he found unengaging, before following his interests in observing nature. An anecdote highlights his eagerness in collecting beetles. Darwin wrote about his life in his Autobiography.

Darwin became the ship's naturalist on the H.M.S. Beagle, sailing around the world from 1831-1836. Prior to Darwin's work, the dominant view held that species were created and remained unchanged. However, in the 1700s, advances in geology began to challenge this static view. Geologists observed that rocks occur in layers, or strata, with different types of fossils found in different layers. Fossils are preserved remnants or impressions of past organisms. By digging deeper into the strata, one goes further back in time. Fossils can include hard parts like teeth and bones, preserved thin tissues, entire organisms (e.g., frozen or in amber), petrified plant tissue, and imprints like footprints.

The discovery of fossil records showed that many types of plants and animals had gone extinct, and ancient fossil layers did not contain today's species, raising questions about the idea of fixed, created species. Geologists like Charles Lyell proposed the concept of uniformitarianism, suggesting that the gradual geological processes occurring today were also at work in the past. Lyell argued that very gradual changes over long periods could result in large physical features like mountains and canyons, implying the Earth must be very old (estimated at 4.6 billion years). Lyell's writings influenced Darwin by suggesting the Earth was old enough for slow processes to result in big changes over long periods.

Before Darwin, some naturalists believed species changed over time but proposed different mechanisms. One notable figure was Jean Baptiste Lamarck, who suggested organisms evolved by the inheritance of acquired characteristics. This idea proposed that an organism could change during its lifetime to adapt to its environment and then pass that acquired trait to its offspring, such as a giraffe stretching its neck to make it longer and passing that longer neck trait on.

During his Beagle voyage, Darwin observed plants and animals along the coasts of South America and the Galapagos Islands. He noted that Galapagos species were similar to those on the South American continent but also adapted to each other and their specific island environments, such as tortoises and cacti, and finches with different beaks.

In addition to his observations, Darwin was influenced by the writings of Lyell and Thomas Malthus. Malthus was an economist who wrote about the exponential population growth of humans and resulting famines. Malthus noted that the power of population growth exceeded the Earth's ability to produce enough food, leading to "premature death". Darwin extrapolated Malthus's ideas to all creatures, reasoning that all species could reproduce faster than their food supplies if unchecked, leading to competition between individuals.

Darwin was also aware of artificial selection, where humans select for desirable traits to create varieties of plants and animal breeds. Examples include the diverse forms of vegetables like broccoli, cabbage, and cauliflower, derived from a kale-like ancestor through human selection, and the wide variety of dog breeds created through artificial selection.

Putting these ideas together, Darwin developed his theory of evolution by natural selection, which he called "Descent with Modification". This concept suggested that descendants were genetically modified through interaction with their environment. Natural Selection itself is defined as "the differential survival and reproduction of individuals with different inheritable characteristics".

The core principles of the Theory of Natural Selection are:

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Every species can produce more offspring than can survive to maturity.

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Population sizes tend to remain constant, limited by the environment.

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There is competition for survival and reproduction.

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Individuals within populations vary in traits affecting their survival chances.

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THEREFORE, individuals with the best traits will survive and reproduce better than other individuals.

Independently, a young British naturalist named Alfred Russel Wallace also developed the theory of natural selection while studying in the East Indies. Wallace's work spurred Darwin's publication of On the Origin of Species in 1859.

Today, Darwin's theory is further supported by modern genetics, forming the basis of the "Modern Synthesis" or "Synthetic Theory of Evolution". An example illustrating evolutionary change is the development of antibiotic resistance, such as Methicillin-resistant Staphylococcus aureus (MRSA), which has spread in various settings.

Evidence supporting evolution comes from several areas:

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Fossils: The oldest known fossils (from ~3.5 billion years ago) are prokaryotic cells. Fossils trace macroevolutionary changes in a chronology, such as the evolution of vertebrates from fishes to amphibians, reptiles, mammals, and then birds. The Tiktaalik, a 375 million-year-old transitional fish, is considered a missing link between sea life and land life and a predecessor of amphibians.

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Comparative Anatomy: Comparing body structures between species reveals similarities. Homologous structures, like the forelimbs of different mammals, are derived from the same ancestral structure but modified for different functions, indicating common ancestry.

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Comparative Embryology: Comparing structures during the early development of different organisms shows similarities. All vertebrates, for example, show similarities like gill pouches and a post-anal tail in embryonic development. An interactive website is mentioned for exploring this.

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Molecular Biology: Comparing genes and proteins between species shows that the more similar the genetic code, the more closely related the species are. All species share the same genetic code.

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Biogeography: The study of the geographical distribution of species provided important evidence for Darwin. He noted that species on the Galapagos Islands were more similar to those on the nearby South American continent than to species on distant islands. Geographically close species are more likely to be related than geographically distant ones.

The sources then delve into Microevolution and Population Genetics. Evolution is defined as a change in allele frequencies in a population over time. A population is all individuals of a single species in a particular area. Microevolution is evolution at the smallest scale: a change in the genetic makeup of a population from generation to generation.

It is crucial to note that evolution occurs at the population level, not the individual level. Changes an individual undergoes during its lifetime (acquired traits) are not genetically coded and therefore do not influence future gene pools. The smallest biological unit that can evolve is a population.

Mutations are the source of all genetic variation. They can involve single genes, or larger changes like deletions, additions, duplications, or omissions of chromosome segments or entire chromosomes.

The Hardy-Weinberg Equilibrium describes a theoretical state where a population is not evolving. This equilibrium requires five conditions to be met:

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The population is infinitely large (to avoid genetic drift).

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There is no mutation.

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There is no gene flow between populations.

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Mating is random.

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There is no natural selection.

If all these conditions are met, allele frequencies remain constant over time. Evolution occurs when any of these five conditions are not met. In nature, these conditions are never perfectly met, but they can be modeled using computer simulations.

Calculating allele frequencies involves understanding the gene pool, which consists of all alleles in all individuals in a population. In a diploid population, there are two copies of each gene per individual. The source provides an example calculation for a population of wildflowers with purple (P) and white (p) alleles.

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p represents the frequency of the dominant allele.

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q represents the frequency of the recessive allele.

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The total frequency of alleles is p + q = 1. If the frequency of one allele is known and only two alleles exist for the trait, the frequency of the other can be calculated.

The Hardy-Weinberg formula (p² + 2pq + q² = 1) relates allele frequencies to genotype frequencies.

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p² is the frequency of homozygous dominants.

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2pq is the frequency of heterozygotes.

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q² is the frequency of homozygous recessives. These genotype frequencies must sum to 1 (or 100%). The source includes practice problems related to calculating allele and genotype frequencies.

Natural Selection and Adaptive Evolution make populations better adapted to their environment. While new traits originate from random mutation, natural selection itself is not random; it favors genes that increase fitness in a given environment, making them more common. Fitness is defined as an individual's contribution to the next generation's gene pool relative to others. Natural selection can have three possible outcomes on the range of phenotypes in a population:

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Directional Selection: Favors phenotypes at one extreme of the range.

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Stabilizing Selection: Favors phenotypes in the middle of the range.

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Diversifying Selection (aka Disruptive Selection): Favors phenotypes at both extremes of the range.

Other mechanisms besides natural selection can cause evolution:

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Genetic Drift: A random change in allele frequencies, more likely in smaller populations, which can lead to a loss of genetic diversity. This is particularly concerning for endangered species. Special cases include the Founder Effect (a new population founded by few individuals) and the Bottleneck Effect (population size drastically reduced, leaving few individuals to contribute genes).

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Sexual Selection: Non-random mating and competition for mates. It stems from the fundamental asymmetry of sex: female fitness is limited by resources for eggs/young, while male fitness is limited by the ability to attract mates. This includes Intrasexual selection (competition among members of the same sex, like male/male competition for female attention) and Intersexual selection (mate choice, where individuals of one sex, typically females, are choosy in selecting partners).

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Gene Flow: The exchange of genes between populations. It can spread beneficial alleles. If gene flow is stopped, it can lead to in-breeding and loss of genetic diversity in small populations, and over long periods, genetically isolated populations may diverge into new species.