Evolution Summary

EVOLUTION

Charles Darwin 

  was the first to theorize evolution by means of natural selection. Evolution by natural selection is a process that includes:
1) more offspring are produced than what can possibly survive
2) traits vary among individuals, leading to different rates of survival and reproduction 
3) trait differences are heritable
       Thus, when members of a population die they are replaced by the progeny of parents better adapted to survive and reproduce in the environment in which natural selection takes place. This creates and preserves traits that are supposedly fitted for the functional roles that they  are to perform. Natural selection is not the only known cause of evolution, other nonadaptive causes of evolution include mutation and genetic drift. (I do not personally believe in evolution, but for those who view the blog posts, this is for my AP Biology class.)

Hardy Weinberg

The Hardy–Weinberg principle (also known as the Hardy–Weinberg equilibrium)

- that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. These influences include non-random mating, mutation, natural selection, genetic drift, and gene flow.

  Because one or more of these influences are typically present in real populations, the Hardy–Weinberg principle describes an ideal condition against which the effects of these influences can be observed.

For example, a single fly with two alleles with frequencies (A) = p and (a) = q, respectively, the expected genotype frequencies are (AA) = p2 for the AA homozygotes, (aa) = q2 for the aa homozygotes, and (Aa) = 2pq for the heterozygotes. The genotype proportions p^2, 2pq, and q^2 are called the Hardy-Weinberg proportions. p + q must be equal to 1, and p^2 + 2pq + q^2=1.

DNA Replication

DNA Replication was proved to be a semiconservative process by Meselson and Stahl.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCgQuAIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DzdDkiRw1PdU&ei=NjoaU8fxCerK2gWi4ICYBw&usg=AFQjCNHRJWSYxmAk66QzMUue1M9WtSw8Ag&sig2=XQHCtFjUgrgP45e5STukKw&bvm=bv.62578216,d.b2I
 Here is a short DNA replication animation.

DNA replication-is the process that makes two identical strands from one parental DNA segment.

     This process starts in the genome, the unwinding of DNA at the origin and synthesis of new strands result in replication forks growing out of the genome. DNA polymerase synthesizes the new DNA by adding complementary nucleotides in codons to the template strand. AGG, etc. DNA is always synthesized in a 5' to 3' direction.
     The leading strand is the strand of  DNA which is being synthesized in the same direction as the growing replication fork. A polymerase reads the leading strand template and adds complementary nucleotides to the leading strand on a continuing basis.
    The lagging strand is the strand of DNA whose direction of synthesis is opposite to the direction of the growing replication fork.
On the lagging strand template, a primase reads the template DNA and begins synthesis of a short complementary RNA primer. A DNA polymerase extends the primed segments, forming Okazaki fragments. The RNA primers are then removed and replaced with DNA, and the fragments of DNA are joined together by DNA ligase.

DNA is the "Transforming Factor"

The "Transforming Factor"

Frederick Griffith (1908)

Frederick Griffith was working with streptococcus pneumonia bacteria. He was trying to find a cure for pneumonia.

The Experiment

He injected heat-killed bacteria into the mice and nothing happened.
He injected the live bacteria into the mice and nothing happened, but when he mixed the heat-killed bacteria with the live bacteria, together the two were able to kill the mice, or infect it with disease. *substance passed from dead bacteria to live bacteria= the "transforming factor".

DNA is the "Transforming Factor"

Avery, McCarty, & Macleod (1944)

They purified both DNA and proteins from streptococcus pneumonia bacteria.
Question: Which will transform non-pathogenic bacteria?

injected protein into bacteria= no effect.
injected DNA into bacteria= transformed harmless bacteria into virulent bacteria.

Confirmation of DNA

Hershey & Chase (1952)

Classic blender experiment

 

Worked with bacteriophages. *viruses that infect bacteria.

They grew phage viruses in 2 media, and radioactively labeled them with either (35) sulfur, heavy sulfur, in their proteins, and (32) phosphorous, heavy phosphorous, in their DNA.

This experiment confirmed DNA is the "transforming factor".



 

CHI-SQUARED

 

The purpose of a Chi-squared test is to accept or reject a null hypothesis.

The Chi-squared equals the sum of the observed minus the expected; squared and then divided by the expected.

The Null Hypothesis- There is no significant difference between the observed and the expected frequencies.

We take the possibilities minus one to find the degrees of freedom.

Critical Values- the number that determines if we accept or reject the null hypothesis. If the number is > than the critical value; reject.

If the number is < or = to the critical value; accept.

*Critical values don't have to be a whole number.

The Cell Cycle

   

Interphase is the longest phase or part of the cell cycle and takes most of the time to complete. It contains three phases: G1, S, and G2.
During the G1 phase the cell focuses mainly on cell growth and its daily metabolic roles. The S phase is rather important because this is when DNA synthesis occurs. The G2 phase involves growth and then makes preparations to launch itself into mitosis.

Mitosis involves Prophase, Metaphase, Anaphase, and Telophase.

Prophase  is the first phase in mitosis. This is when the chromosomes condense and become visible, the nuclear membrane breaks down and the spindle apparatus forms at opposite poles of the cell.

Metaphase is the second phase in mitosis, and how I remember this phase apart from the others is "meta=middle". The chromosomes align themselves along the metaphase plate. Right through the middle of the cell, all aligned.

Anaphase is the 3rd phase in Mitosis, when the chromosomes split and the sister chromatids move to opposite poles of the cell.

 Telophase   is the final stage of mitosis, this is when the nuclear envelope forms and the daughter cells split into new cells.

Cytokinesis is the final stage in the Cell Cycle. This is the division of the cytoplasm of the cell, following mitosis.