To understand evolution, one must realize that evolution is almost never about an individual; and it is almost never abrupt—occurring in one generation. That implies that one must understand what happens to whole populations—to see the forest, and not just the individual pine trees.
14. Population Genetics: The Hardy-Weinberg Theorem states that the genotype and allele frequencies of a population will remain constant from one generation to the next if the population has the following characteristics: large size, no gene flow into or out of the population, no mutations, random mating, and no natural selection. A population that meets all of those requirements is described as being in Hardy-Weinberg equilibrium and is not evolving. Of course very few populations are ever in such strict equilibrium. Population geneticists construct a theoretical H-W equilibrium and compare it to the real state in nature. A deviation from the state of equilibrium is evidence that the population is adapting and that the process of microevolution is taking place. Molecular biologists–evo-devo scientists–can look into the genome of the members of the population to determine what alterations have occurred that are establishing that change.
The two allele Hardy-Weinberg equation is p2+2pq+q2=q2+1, where p equals the frequency of allele A; q equals the frequency of allele B; p2 equals the frequency of genotype AA; 2pq equals the frequency of the prototype AB; and q2 equals the frequency of the prototype BB. Each organism contains two alleles, either a homogenous pair (for example, AA or BB), or a heterogeneous pair (for example AB). Geneticists can determine the frequency of one allele given the frequency of the other. According to the Hardy-Weinberg equation, the combined frequencies of the two alleles—the frequency of allele A (p) plus the frequency of allele B (q)—must equal 1. Because p+q=1, if the value of p is known, the value of q is found using the equation q=1-p.
The processes involved in developing, maintaining, or changing populations and eventually resulting in speciation and evolution are:
- Gene amplification: an increase in the frequency of replication of a DNA segment, which may be induced by a polymerase chain reaction.
- Gene drift: unpredictable, chance changes in allele frequencies that cause one allele to become more common in a population than another allele. Drift may occur slowly over time or may come about due to a sudden decrease in population size.
- Gene flow: the alteration of the frequencies of alleles of particular genes in a population, resulting from the interbreeding with organisms from another population having different frequencies.
- Gene frequency: the frequency of occurrence or proportions of different alleles of a particular gene in a given population.
- Gene pool: the total genetic information in the gametes of all the individuals in a population.
- Gene transcription: the genetic information in DNA is transcribed or rewritten onto a strand of messenger RNA (mRNA). Transcription occurs when DNA is unwound, and one strand serves as the template of mRNA.
- Gene translation: during translation, the information on the mRNA is used to assemble a new protein. During translation, the three base sequences on the mRNA called codones specify the sequence of amino acids to be assembled in the creation of a specific protein. Ribosomes assist in protein synthesis by serving as docking points for tRNAs–amino acid-carrying molecules that bond to the mRNA condone.
- Gene expression: the synthesis of proteins according to information encoded in DNA. The timing and frequency of gene expression is controlled by many factors in the cell.
- Gene regulation: In prokaryotes, the regulation occurs via activators and repressors that promote or reduce transcription. In eukaryotes, regulation occurs via both transcriptional and posttranscriptional control. Proteins called transcription factors are required for transcription to begin, and proteins called enhancers activate transcription. The mRNA is processed after transcription. Introns are spliced and a cap and tail are added to the mRNA. Posttranscriptional controls in eukaryotes include RNA splicing, transporting the mRNA out of the nucleus, selective destruction of mtRNA, selective destruction of proteins, and selective translation of mRN.
16. Science: Science is an active discipline wherein working hypotheses are put forward and facts are accumulated to develop a concept and finally are sufficient to support or refute a theory over time until the theory achieves a level of validity to be considered a fact or a law of nature. For example, the physical theory or law of gravity related to the attraction of two objects proportional to their mass—the first force to be described in mathematical terms–or the chemical theory or law defining water as a combination of two parts hydrogen united with one part oxygen on a molecular level are firmly established and considered to be irrefutable. In science–as opposed to religion or science fiction–experiments must by performed, and the methodology of those experiments must allow for disapproval and negation of the hypothesis as well as providing positive proof of the correctness of the hypothesis. Knowledge from experimentation may lead to new ideas and explanations that reveal the incompleteness or deficiencies of previous explanations. Doubt in science is considered crucial to finding the truth; whereas, in religion, doubt is usually considered to be inappropriate or outright anathema. continued…