ACE BIO: Chapter 1 Origin of life review

• Origin of life;

https://www.khanacademy.org/science/biology/history-of-life-on-earth/history-life-on-earth/v/origins-of-life

This chapter covers the origins of life. In most of the Canadian curriculum of biology courses, in universities and high schools, we do not talk much about the origins of life. So, many students have little back ground in this area. This thread is to highlight the most important topics that you will likely encounter on the cDAT.

Primordial Earth and Organic soup theory by Oparin and Haldane:

The theory of how life began was suggested by two scientists Oparin and Haldane. They suggested that Earth had a reducing atmosphere and an oxygen poor environment. The inorganic substances in the reducing environment would donate electrons and form a series of chemical reactions catalyzed by energy from lightnings, UV radiation and volcanic eruptions which gave rise to organic substances and formed the primary proteins and nucleic acid polymers. They further suggested that these polymers formed colonies which were able to replicate themselves, forming primary ribonucleic acids, and later on they were enclosed in membranes different from the environment, giving rise to functioning cell like structures, called "protobionts". The theory is based on a continuous build up of simple structures giving rise to more complex ones, forming cell like structures.

Primordial Soup is a term that refers to the early environment of earth that consisted of a mixture of gases that gave rise to organic polymers under the reducing environment. The mixture of compounds that were present in the primordial soup were hypothesized to consist mainly of 5 gases, CH4, NH3, CO2, N2, H2. Methane, Ammonia, Carbon dioxide and Nitrogen and hydrogen gas. [How to remember the gases --> the famous news channel CCNN-H].

Miller-Urey Experiment: to test the hypothesis of organic soup theory, Miller and Urey synthesized an experiment to test the theory. Using a heated pool of water and a mixture of gases , CH4, NH3, N2, H2, H2O, and chemical energy from lightning translated with an electric spark, managed to recreate the primary earth conditions. The experiment resulted in formation of various types of amino acids, sugars, lipids, and other organic molecules. However, larger more complex organic molecules, like nucleic acid were missing, but this experiment showcased that under abiotic conditions, organic compounds that are building blocks of larger more complex molecules can form spontaneously.

Ribozymes- RNA enzymes or catalysts that catalyze synthesis of RNA polymers. They are a major component of RNA- world hypothesis.

Evolution

https://www.khanacademy.org/science/high-school-biology/hs-evolution/hs-evolution-and-natural-selection/v/introduction-to-evolution-and-natural-selection

Natural selection: is the basic mechanism of evolution that was proposed by Darwin. If there is variation in traits, differential reproduction and heredity, there will be evolution by natural selection as an outcome. In order for evolution to occur by natural selection there must be;

1. Variation in traits- some traits in the population prove more advantageous providing a higher chance of survival.

2. Differential reproduction and sexual selection- some traits prove more appealing and thus are selected for to increase survival rate, and the environment has a carrying capacity in which it can support individuals, and prevents unlimited population growth.

3. Genetic mutation- variation in traits are introduced within the population which can be selected for or against in the following generation.

4. Genetic drift- the change in the frequency of an allele in the population, due to random sampling of the population, over time. The alleles in the offspring are inherited from the parents and chance determines whether the offspring will survive and the allele will be passed on to the next offspring.

5. Migration or gene flow- it is the transfer of genetic material from one population to the another

Sexual selection is a theory that dictates the mating process between two sexes of a population, intersexual selection, is non-random, and the traits are chosen by one of the sexes and are deemed as more favourable because it would indicate increased chance of survival for the offspring.

Inheritance of variations- is the assumption that traits are heritable and they are passed on from parents to offspring in a non-random process of selection.

Speciation- is the evolutionary process in which populations evolve and become distinct species. The key word here is populations, since only populations evolve not individuals. there are two types of speciation process;

1. Allopatric speciation- is the process of speciation that occurs when one population develops into two distinct populations in response to a form of geographical barrier that prevents the population form interbreeding, stopping gene flow. They diverge so much so that they are no longer compatible to mate with one another, forming two distinct species.

2. Sympatric speciation- is the evolution of one species into two distinct species in response to a chance mutation that causes the species to no longer interbreed and as a result become two distinct species in the same region. The population of the species that occupy the same habitat become reproductively isolated from each and it most commonly occurs through polyploidy, common in plants.

Convergent evolution- is the independent development of similar features in different species overtime, due to common selective pressures in the environment. Example would be development of wings in Birds, and Bats.

Divergent evolution- is the process of species from a common ancestor evolving and accumulating differences overtime that results in development of new species, which can be due to environmental factors and selective pressures of the population.

Parallel evolution- is the similar development of traits in to different species that are not closely related but share a similar trait that is under an evolutionary pressure.

Adaptive radiation- is the process of divergence of one species into distinct species through adapting to different habitats within the same environment. It commonly occurs when the environment presents new challenges, resources, and niches, and introduces new selective pressures on the species in the environment. Example, Darwin's Finches on the Galapagos islands.

Focus on questions of adaptive radiation vs divergent evolution, the differences between the two.

POPULATION GENETICS:

The Hardy Weinberg Principle and equation and use in a problem

https://www.khanacademy.org/science/biology/her/heredity-and-genetics/v/hardy-weinberg

Hardy Weinberg equilibrium

The Hardy-Weinberg Theory is based on Mendelian genetics, dealing with diploid organisms, that reproduce via sexual reproduction. In this context, it is used as a predictor of genotype frequencies, and allelic frequencies within a population that follows a set of assumptions:

the population is at equilibrium when:

1. No natural selection. Natural selection is not acting on the genes , meaning that there are no differential survival rates with respect to heritable traits.

2. No mutation. Lack of genetic mutation prevents the introduction of new alleles within the population

3. No gene flow. there is no gene flow between populations that could introduce new alleles into the population.

4. No genetic drift. Population size is infinite, and genetic drift is not causing random changes in allele frequencies due to sampling error from one generation to the next.

5. Random Mating. Individuals in the population mate randomly.

• Allele frequencies are equal in the sexes -- no allelic advantage

• There is no migration, gene flow, admixture, mutation or selection

The following assumptions will give rise to a population that is at Hardy Weinberg equilibrium, and following these assumptions the genotype frequencies can be predicted for; using 2 sets of equations with 2 alleles of the same gene--> p=A, q= a --> AA, Aa, aa

1. p+q=1

2. p^2+2pq+q^2=1

• p is dominant allele of a genotype, the frequency of allele p= 1-q

• q is recessive allele of a genotype, the frequency of allele q=1-p

• p^2= the genotypic frequency of homozygous dominant genotype in the population

• q^2= the genotypic frequency of homozygous recessive genotype in the population

• 2pq= the genotypic frequency of heterozygous genotype in the population

the assumptions of this theory:

1. allele frequencies in a population will not change from generation to generation.

2. If the allele frequencies in a population with two alleles at a locus are p and q, then the expected genotype frequencies are p2, 2pq, and q2. This frequency distribution will not change from generation to generation once a population is in Hardy-Weinberg equilibrium. For example, if the frequency of allele A in the population is p and the frequency of allele a in the population is q, then the frequency of genotype AA = p2, the frequency of genotype Aa = 2pq, and the frequency of genotype aa = q2. If there are only two alleles at a locus, then p + q , by mathematical necessity, equals one. The Hardy-Weinberg genotype frequencies, p2 + 2pq + q2, represent the binomial expansion of (p + q)2, and also sum to one (as must the frequencies of all genotypes in any population, whether it is in Hardy-Weinberg equilibrium). It is possible to apply the Hardy-Weinberg Theorem to loci with more than two alleles, in which case the expected genotype frequencies are given by the multinomial expansion for all k alleles segregating in the population: (p1 + p2 + p3 + . . . + pk)2.

Microevolution- the changes in allele frequencies at the individual level that occur overtime. This change in allelic frequency is through four different processes;

1. mutation

2. natural/ artificial selection

3. gene flow

4. genetic drift

Mutation- is the chance occurrence of errors in genetic makeup or alterations in the nucleotide sequence of the genome through either errors in DNA machinery or environmental inducers such as UV light .

Assortative mating- is the process of random mating pattern where individuals are more likely to mate with other individuals that share similar phenotypes with one another more frequently than random mating.

Parsimony is the theory that the least number of assumption made in a lineage is the most valid, minimizing homoplasy or assumptions of homoplasy.

Homoplasy is when a trait has been gained or lost independently in separate lineages over the course of evolution.

Comparative anatomy

Homologous structure- are structures that are similar in organisms that suggest a common ancestry, may not look exactly look the same or have a similar function.

Analogous structures- are similar structures that evolved independently in two living organisms to serve the same purpose, without presence of a common ancestor. Analogous structures are examples of convergent evolution where two organisms separately have to solve the same evolutionary problem in similar ways with similar environments.

For your enjoyment!