Evolution and Genetics

Mechanisms of Change

Charles Darwin (1809-1882), grandson of the physician Erasmus Darwin (1731-1802) and

Gregor Mendel (1822-1884), a monk who lived in an abbey in what is now the Czech Republic, never met, but their pioneering work gives us the framework to understand biological change at molecular, individual organism, and broader ecosystemic levels.

Charles Darwin1809-1882

Gregor Mendel1822-1884

Factors Creating Variation

• mutation (random alteration in gene)

An error in replication or other alteration of the nucleotide base sequence creating a change in the sequence of base pairs on a DNA molecule.

• gene flow (genetic exchange between two populations)

Factors Sorting Variation

• natural selection the concept that genes which produce

characteristics that are more favorable in a given environment will be more abundant in the next generation

• gene drift is evolution occurring through random changes in

allele frequency over time. The effects of genetic drift are strongest in small populations. The main result of genetic drift is loss of genetic variation.

What is a Cell? A cell is the smallest living unit,

the basic structural and functional unit of all living matter, whether that is a plant, an animal or a fungus.

Some organisms (amoebae,

bacteria, some algae and fungi) are single-celled.

Humans are quite different and

are made up of approximately 3 trillion cells (3,000,000,000,000 cells).

Cells of higher organisms (e.g. plant or animal) are composed of:

• a cell MEMBRANE enclosing the whole cell. (Plant cells have an additional cell wall for structural reinforcement.)

• many ORGANELLES, which are functional components equivalent to the organs in the body of an animal e.g. for digestion, storage, excretion.

• a NUCLEUS, the command center of the cell. It contains all the vital information needed by the cell or the whole organism to function, grow and reproduce. This information is stored in the form of a genetic code on the chromosomes, which are situated inside the nucleus.

What is a Stem Cell?• These are primitive cells in marrow that are required to make red

cells, white cells and platelets.

• Stem cells are largely found in the marrow but some leave the marrow and circulate in the blood.

• Using special techniques, the stem cells in blood can be collected, preserved by freezing and, later, thawed and used for stem cell therapy.

• The ethics of stem cell research are hotly debated, as the major source of stem cells has been embryos. Last week, researchers announced that it is possible to harvest adult stem cells.

Proteins

• are the basic building materials of a cell, made by the cell itself. They consist of a chain of amino acids, small specific building blocks that easily link up.

• proteins are crucial in the formation of cells and in giving cells the capacity to function properly.

Chromosomes• means ‘colored bodies’ (they can be seen under the light microscope, using

a particular stain).

• they look like bundled up knots and loops of a long thin thread. Chromosomes are the storage place for all genetic (hereditary) information.

• this information is written along the thin thread, called DNA.

• DNA (deoxyribo-nucleic acid) is an acidic material that can be found in the nucleus. The genetic information is written in the form of a code, almost like a music tape.

• to ensure the thread and the information are stable and safe, a twisted double stranded thread is used-the famous double helix. When a cell multiplies it will also copy all the DNA and pass it on to the daughter cell.

Genome

• is the totality of the genetic information of an organism.

• Human cells possess two sets of 23 different chromosomes, one set from the mother and the other from the father.

• Stretched out, the DNA of each human cell would be two meters long. It is thus crucial to organize the DNA in chromosomes to avoid knots, tangles and breakages (see Mutation).

DNA

• Information contained on the chromosomes in the DNA is written, coded, and understood by living organisms.

• In this coding system, cells need only four symbols (called nucleotides) to spell out all the instructions of how to make any protein.

• Nucleotides are the units that compose DNA and their individual names are commonly abbreviated to the letters A, C G and T

• These letters are arranged in 3-letter words which in turn code for a particular amino acid.

The Gene

• is a certain segment (length) of DNA with specific instructions for the production of one specific protein.

• Genes are portions of the DNA molecule that direct the development of an identifiable trait.

• Genes are maps and strategies for growth and life functions.

The Gene Pool• is the total of all genes present

in a population.

• Although biologically they could breed with any members of their species, an isolated population is a breeding group whose members breed mostly or solely among themselves, usually as a result of physical isolation (gene drift).

• Immigration may result in the addition of new genetic material to the established gene pool of a population (gene flow).

Alleles

• Are alternative forms of a gene

• Eye color is an example

Genotype and PhenotypeGenotype is the actual genetic composition of an organism.

Phenotype is the physical, outward appearance of an organism.

A change in the environment can affect the phenotype. Although we think of flamingos as being pink, pinkness is not encoded into their genotype. The food they eat makes their phenotype white or pink.

Chromozomes

• Chromozomes occur in pairs

• Humans have 23 x 2 chromozomes, one set from each parent

• The 23rd chromosome determines sex

(xx = female, xy = male)

Genetic Traits

• Most genetic traits are non-concordant (that is, height or eye color does not predict skin color)

• Most traits are clinal (the percentage of a population with a trait varies incrementally over geographical space

temperature clines

genetic clines

Independent Assortment(non-concordance)

• Harvard University geneticist and evolutionary biologist Richard Lewontin’s famous 1972 computer analysis finally swept the old race categories out of biology (see his article in Podolefsky and Brown).

• ‘The races are primarily defined according to skin color, which is a genetic trait,’ he says. ‘The question I asked was, if you looked at two people of different races, would there be other genetic differences between them?’

• The results confounded the old assumption that there are profound biological differences between the races.

Lewontin’s Findings• And of that variable amount, 85 per cent of the difference would be

present even if the two people were fairly closely related; that is, an ethnic subgroup, like Norwegians.

• Another 9 per cent of the genetic variation results from individuals being members of geographically separated societies––a Spaniard and an Italian, for example.

• Of all human genes, about 75 per cent are identical in every person; only 25 per cent vary from person to person.

• And only about 6 per cent is the result of the two people being from what we call separate races, based on what we see (phenotype).

There is no Biological Race

• Hence, Professor Lewontin discovered that any person’s “race” acounts for only about 0.24 per cent (6 per cent of 25 per cent) of her/his genetic make-up.

Evolution

• may be seen as the continual change in the frequency of certain genes in a population in response to the demands of the environment (climate, resources, etc)

• Thus, the ecological/environmental context is the source of what is termed ‘natural selection.’

Genetics and Contemporary Society

• What are the implications?

Ethical and Religious Implications of Cloning

• Isn’t this Playing God?

• What are Clones?• What are their

Rights?• Will there be two

groups, Humans and cloned Slaves?

Social and Economic Implications of Genetic Engineering

• Who can Benefit?

• Who will Pay?

• Who Owns the New Organisms?

Medical Implications

• What are the benefits?

• Will this change the ability of humans to Adapt?

• Are there hidden risks?

Environmental Implications

• What are the benefits of genetically modified foods?

• What are the risks?

• Will this change the ability of both plants and humans to adapt?

Bt corn

Environmental Implications

• Will this alter “natural” Evolution?

• Is the gene plasm of fundamental crops (maize for example) at risk?

• What are the implications for Warfare and Terrorism?

Technical Issues

• The not-very accurate Gene Gun: trout genes in strawberries

• Containment: escaping BT corn pollen, gene-altered trout from aquaculture farms

• Genetic clean-up: how to sanitize bioterrorism incidents researcher maps trout

genome to increase production

Our Brave New World