Chapter 25: The History of Life on Earth

3 Main Questions:

-What is ribozymes?

An RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing.

- What is protobiont?

A collection of abiotically produced molecules surrounded by a membrane or membrane-like structure.

- What is half-life?

The amount of time it takes for 50% of a sample of a radioactive isotope to decay.

5 Main Facts:

- The earliest evidence of life on Earth comes from fossils of microorganisms that are about 3.5 billions years old.

- There is scientific evidence that Earth and the other planets of the solar system formed about 4.6 billion years ago, condensing from a vast cloud of dust and rocks that surrounded the young sun.

- As the bombardment of early Earth slowed, conditions on the planet were extremely different from those of today.

- It is unclear whether the atmosphere of young Earth contained enough methane and ammonia to be reducing.

- The presence of small organic molecules, such as amino acids, is not sufficient for the emergence of life as we know it.

Diagram:

The proposed ancestors of mitochondria were aerobic, heterotrophic prokaryotes (meaning they used oxygen to metabolize organic molecules obtained from other organisms). The proposed ancestors of plastids were photsynthetic prokaryotes.

Summary:

Conditions on early Earth made the origin of life possible. The earliest evidence of life on Earth comes from fossils of microorganisms that are about 3.5 billion years old. The hypothesize that chemical and physical processes on early Earth, aided by the emerging force of natural selection, could have produced very simple cells.

For the first few hundred million years, life probably could not have originated or survived on Earth because the planet was still being bombarded by huge chunks of rock and ice left over from the formation of the solar system.

Video:

http://www.youtube.com/watch?v=uVrzNR_UK_4

Chapter 24: The Origin of Species

3 Main Questions:

- What is speciation?

An evolutionary process in which one species splits into two or more species.

- What is macroevolution?

Evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time.

- What is biological species concept?

Definition of a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.

5 Main Facts:

- A species may originate from an accident during cell division that results in extra sets of chromosomes, a condition called polyploidy.

- A second form of polyploidy can occur when two different species interbreed and produce hybrid offspring.

- Many hybrid zones are stable in the sense that hybrids continue to be produced.

- The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then dissappear.

- The punctuated pattern suggests that once the process begins, speciation can be completed relatively repidly a suggestion confirmed by a growing number of studies.

Diagram:

A mutation in one gene cayses the shell of the Japanese land snail (a) to spiral in the opposite

direction from others. Snails with opposite spirals cannot mate, resulting in reproductive isolation.

Summary:

The "mystery of mysteries" that captivated Darwin is speciation, the process by which one species

Speciation fascinated Darwin and many other biologists because it is responsible for the tremendous

diversity of life, repeatedly yielding new species that differ from existing ones.

Speciation also forms a conceptual bridge between mocroevolution, changes over time in allele

frequencies in a population, and macroevolution, the broad pattern of evolution over the long time

spans.

Video:

http://www.youtube.com/watch?v=vfmOaAz371M

Chapter 23: The Evolution of Populations

3 Main Questions:

- What is microevolution?

Evolutionary change below the species level; change in the allele frequencies in a population over generations.

- What is mutation?

A change in the nucleotide sequence of an organism's DNA, ultimately creating genetic diversity. Mutations also can occur in the DNA or RNA of a virus.

- What is a gene pool?

The aggregate of all of the alleles for all of the loci in all individuals in a population. The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population.

5 Main Facts:

- Character that vary within a population may be discrete or quantitative.

- Average heterozygosity is often estimated by surveying the protein products of genes using gel electrophoresis.

- Nucleotide variability is measured by comparing the DNA sequences of two individuals in a population and then averaging the data from many such comparisons.

- Chromosomal changes that delete, disrupt, or rearrange many loci at once are almost certain to be harmful.

- In organisms that reproduce sexually, most of the genetic variation in a population results fromthe unique combination of alleles that each individual receives.

Diagram:

The small wildflower population has a stable size of ten plants. Suppose that by chance only five plants (those in white boxes) of generation 1 produce fertile offspring. This could occur, for example, if only those plants happened to be grow in a location that preovided enough nutrients to support the production of offspring. Again by chance, only two plants of generation 2 leave fertile offspring. As a result, by chance alone, the frequencies of the a allele first increases in generation 2, then falls to zero in generation 3.

Summary:

One common misconception about evolution is that individual organisms evolve. Focusing on evolutionary change in populations, we can define evolution on its smallest scale, called microevolution, as change in allele frequencies in a population over generations.

Natural selection is not the only cause of microevolution. In fact there are three main mechanisms that can cause allele frequencies change: natural selection, genetic drift(chance events that alter allele frequencies), and gene flow (the transfer of alleles between populations).

Video:

http://www.youtube.com/watch?v=MzKQfrb8Dh4

Chapter 23: The Evolution of Populations

Chapter 22: Descent with Modification a Darwinian View of Life

3 Main Questions:

- What is evolution?

Descent with modification; the idea that living species are descendants of ancestral species that were different from the present day one.

- What is strata?

A rock layer formed when new layers of sediment cover older ones and compressed them.

- What is uniformitarianism?

The principle stating that mechanisms of change are constant over time

5 Main Facts:

- During the voyages of the Beagle, Darwin observed many examples of adaptions, characteristics, of organisms that enhance their survival and reproduction in specific environment.

- Darwin viewed the history of life as a tree, with multiple branchings from a trunk out to the tips of the youngest twigs.

- Darwin proposed a mechanism, natural selection, to explain the observable patterns of evolution.

- An organism's trait can influence not only its own performance, but also how well its offspring cope with environmental challenges.

- One subtle but important point is that although natural selection occurs through interactions between individual organisms and their environment, individuals do not evolve.

Diagram:

This evolutionary tree of insect and plant eater and thier relatives is based mainly on fossils - their anatomy, older of appearance in strata, and geographic distribution. Most branches of descent ended in extinction.

Summary:

A century and a half ago, Charles Darwin was inspired to develope a scientific explanation for these three broad observations. When he published his hypothesis in The origin of species, Darwin ushered in a scientific revolution the era of evolutionary biology.

Evolution as descent with modification, a phrase Darwin used in proposing that Earth's many species are descendants of ancestral species that were differnent from the present day species.

Video:

http://www.youtube.com/watch#!v=GcjgWov7mTM&feature=related

Chapter 21: Genomes and Thier Evolution

3 Main Questions:

- What is genomic?

The study of whole sets of genes and their interaction.

- What is bioinformatics:

The use of computers, software, and methematical models to process and itegrate biological from large date sets.

- What is Human Genome Project?

An international collaboartive effort to map and sequence the DNA of the entire human genome.

5 Main Facts:

- The chimpanzee is our closest living relative on the evolutionary of life.

- Using available DNA sequences, geneticists can study genes directly, without having to infer genotype from phenotype, as in classical genetics.

- The identities of about half of the human genes were known before the Human Genome Project began.

- Sometimes a newly identified sequence will match, at least partially, the sequence of a gene or protein whose function is well known.

- Genomics and proteomics are enabling biologists to approach the study life from an increasingly global prespective.

Diagram:

Whole genome shotgun approach to sequencing. In this approach, developed by Craig Venter and colleagues at the company he founded, Celera Genomics, random DNA fragments are sequenced and then ordered relative to each other.

Summary:

The chimpanzee is our closest relative on the evolutionary tree of life. Its genome was sequenced in 2005, two years after sequencing of the human genome was largely completed. Now that we can compare our genome with that of the chimpanzee base by base.

We can tackle the more general issue of what differences in the genetic information account for the distinct characteristics of these two species of primates. With the genomes of many species fully sequences, scientist can study whole sets of genes and their interactions, an approach called genomics.

Video:

http://www.youtube.com/watch?v=XuUpnAz5y1g

Chapter 21: Genomes and Thier Evolution