I took a course in genetics in 1942 in which an important part was the basic principles of inheritance discovered by Gregor Mendel. In 1910 it was established that chromosomes carry the genes, and we learned how Medelian inheritance is modified according to where a gene is located on a chromosome. At that time I thought of a chromosome as something like a bean pod and the genes like the beans in the pod.

We learned that humans have 23 pairs of chromosomes. One pair is the sex chromosomes. A female has two X chromosomes, and the male has one X and one Y; therefore, the male determines the sex of the offspring. If the winner in the sperm derby carries an X chromosome, the child is a girl (XX). If it carries a Y, it's a boy (XY).

We also learned about meiosis, which is the cell division by which the gametes (eggs and sperm) are formed. Two important things happen during the process of meiosis in the production of eggs and sperm: 1) the double set of chromosomes is reduced in to one set and 2) there is a crossing-over of genes from one chromosome to the other so that chromosomes from each parent do not stay intact, which increases the diversity of offspring.

My genetics professor knew about chromosomes but didn't know much more about genes than Mendel. Gregor Mendel was an obscure Central European monk who discovered the basic principles of inheritance and published a paper on the subject in 1866, but it didn't receive much attention until 1900. Prior to Mendel most scientists thought hybridization results in the blending of traits. However, Mendel found, for example, that in a cross between a pea having a yellow seed with one with green seed you get either yellow or green but not a blend. (You may have seen both yellow and green split peas in the supermarket but not greenish yellow ones.)

Rather than sitting in his monastery cell speculating on God's plan for how inheritance works, Mendel, who was trained in science and mathematics, went to his garden and experimented. He was lucky or smart enough to choose a self-pollinated plant, which breeds true. He crossed green and yellow peas and found that all of the F1 (first generation) peas were yellow. However, in the F2 generation he found that most were yellow and some were green. He counted each group and found a ratio of three yellow to one green. (He saw the same ratio in the F2 generation when he crossed purple flowered peas with white flowered peas.) Mendel theorized that there must be two "factors" related to each trait. The two factors or alleles of the gene for seed color are duplicates in the parent with yellow seed, YY, and in the other parent with green seed, yy. In the F1 generation every plant had the Yy combination and was yellow indicating that the yellow factor is dominant and the green factor is recessive. In the F2 generation the deck is shuffled resulting in 1 YY, 2 Yy (also yellow seed because Y is dominant), and 1 yy (green seed). The YY plants are homozygous for the yellow pea color, and the Yy plants are heterozygous.

When I was in college, I had a summer job in the wheat breeding nursery. The crop breeder had plants that he wanted to cross, and I did the field work. I would remove the anthers (pollen sacks) from parent A and place a bag over the head to keep out unwanted pollen. When the plant was ready to pollinate, I would take anthers from the flower of parent B and sprinkle pollen over the stigma in the flower of parent A. Starting with the F2 generation, the crop breeder would select for desired characters such as yield, insect or disease resistance, straw length, and milling and baking quality. Note that the traditional hybridization reshuffles the genes that are already in the gene pool of a particular crop species by crossing different varieties of crops or breeds of animals. You might call this "genetic engineering lite."

In 1973 Stanley Cohen and Herbert Boyer spliced a gene from a frog into the DNA of a bacterium producing the first recombinant DNA. Genetic engineering or gene splicing, which inserts a gene from one species into another, was born! The steps used were as follows: 1) They used a restriction enzyme to cut the frog's DNA at a specific site. 2) To get the frog DNA into the bacterial cell, they used plasmids (small circular chromosomes) from the cytoplasm of a bacterium. Again, they used a restriction enzyme to cut the DNA in the plasmids. 3) They mixed the frog's DNA with the cut plasmids to form the recombined DNA. The plasmids already contained a critical gene that makes the cell resistant to the antibiotic, tetracycline. 4) The bacteria took up the plasmids, which then multiplied within the bacterial cells. The plasmids were an assortment carrying a variety of frog DNA pieces. 5) They killed the bacteria that didn't take up the altered plasmids by exposing the bacteria to tetracycline. (Remember that the carrier plasmids make the bacteria resistant to the antibiotic.) 6) Now they were faced with the problem of finding the plasmids with the desired piece of frog DNA, i.e., the desired gene. To do this, they used a radioactive marker. (Well, no one ever said the process was easy!)

There are many applications of genetic engineering, but one of the most important and most controversial is genetically modified (GM) crops. If carelessly done, it does have the potential for harm, but if regulated and carefully done, it can produce very important benefits. One application is to splice into the cotton DNA a gene that codes for a compound that is toxic to a certain group of bugs including the cotton bollworm. This reduces the amount of insecticides needed, which have big risks of their own. In each application we need to make a risk/benefit analysis and rationally decide if the benefits are worth the risk.

In 1998 James Thomson isolated human embryonic stem cells, and whether he knew it or not, he created a huge ethical issue. After an ovum is fertilized, it divides over and over to become an embryo or blastocyst consisting of a mass of embryonic stem cells. Animal breeders often separate these cells to clone several copies of a valuable animal.

Embryonic stem cells are capable of developing into any particular tissue of the body. For example, some of these cells from a mouse have produced heart tissue that has been successfully integrated into the heart of mouse. This offers the enticing possibility of repairing damaged hearts or fixing nerve damage in the spinal cord of people.

Where can you find spare embryos? It turns out that surplus embryos are produced in in vitro fertilization. If a woman's oviducts are blocked, the ova can be surgically removed and fertilized with sperm in a culture dish. In Two or three days after the fertilized egg has become eight cells the embryo is placed in the uterus.

Using embryos raises the specter of using potential life for therapeutical purposes. Some people, who are absolutists, don't even want surplus embryos in storage in reproductive clinics used that would otherwise be destroyed.

One way around this ethical problem is to use adult stem cells. Our major adult tissues develop their own tissue-specific stem cells. In an exciting experiment in 1999 Harvard researcher Evan Snyder injected neural stem cells into the brain of a mouse to fix a disease similar to MS in which there are missing neural cells, and it worked. Blood stem cells are often used in humans to replace bone marrow destroyed in cancer therapy. Unfortunately, this can't be applied to many other problems because it isn't always possible to find the specific stem cells needed.

Cloning is very common way of propagating plants. Most fruit trees are cross-pollinated, so they don't breed true. If you plant the seeds of an apple, the seedling trees will rarely produce acceptable apples. All commercial apples are produced on trees that are clones. A twig is cut from a donor tree and grafted on to rootstock.

Natural cloning is also not uncommon in people. If shortly after fertilization, the embryo divides into two embryos, identical twins result. Animal breeders sometimes produce multiple births by dividing the embryo into two or more parts. This type of cloning is the easy way. (A clone is simply "a group of identical genes, cells, or organisms derived from a single ancestor.")

In 1984 Steen Walladsen cloned a sheep by transplanting the nucleus from an undifferentiated early embryo cell to a denucleated egg cell. This was a big step, but it is limited to cloning embryos. The big challenge was to clone adults. It was commonly assumed that once the cells became differentiated it was impossible to clone them.

On July 5, 1997, the impossible happened! A remarkable lamb that was the chip off the old block, was born in Scotland. Ian Wilmut and his team cloned a nucleus from a differentiated mammary cell, so naturally the lamb was named "Dolly." She had no daddy, but she had three mommies: a nucleus donor, a egg cell donor, and a birth mother. Now Dolly is a mommy herself having given birth to a lamb the old-fashioned way proving the genetic viability of a clone.

Cloning Dolly was not easy: Her cloning succeeded only after 277 attempts. The Scottish "midwives" took mammary cells from sheep A and put them in a nutrient poor culture that caused the cells to "dedifferentiate," i.e., becoming capable of forming any tissue. Then they removed the nuclei from egg cells taken from the ovary of sheep B and replaced those nuclei (having one set of 23 chromosomes) with sheep A's nuclei (having the full two sets of chromosomes). They let the egg cells develop into embryos in a culture, and then one was implanted into sheep C. It turns out that Dolly was not an exact copy of sheep A because its mitochondrial DNA came from the egg cell donor, sheep B.

Dolly got the attention of a lot of people because she was cloned from an adult mammal, and if you can clone a sheep, you can probably clone a person, which raises all kinds of thorny ethical and medical issues.

No two people have the same fingerprints, but it is sometimes difficult to interpret fingerprints. DNA "fingerprinting" provides a much higher degree of certainty.

In 1987 the first criminal suspect was convicted based on DNA evidence. On the other side of the coin the Innocence Project alone, which was established in 1992 at the Benjamin N. Cardozo School of Law by attorneys Barry Scheck and Peter Neufeld, has with the use of DNA evidence obtained the exoneration of more than 200 people in the United States, including several who had been sentenced to death. So, DNA "fingerprinting" is a big deal.

In a rapist's case a sample of semen or other biological matter is taken from the victim and a sample of blood is taken from the suspect. If the sample of DNA is too small, a process called PCR (polymerase chain reaction) can make millions of copies of the DNA. It is not necessary to compare the whole genome in each sample. They look for repetitive DNA sequences side by side on a chromosome. One might inherit from his mother a sequence that is repeated 8 times and a sequence from his father that is repeated 4 times. If the DNA from this person is cut with a restriction enzyme, two different sized fragments will be formed and be seen by using gel electrophoresis. Several of these sequences taken together adequately identifies a person's unique pattern.

What is the DNA connection with cancer? Cancer is over a 100 diseases in which there are mutations in the DNA that result in uncontrolled growth of cells. This may be triggered by chemical carcinogens, mutagens such as X-rays, and virus. Molecular biologists isolated genes from human cancer cells and found that gene mutations may either change genes that code for normal growth-stimulating proteins or change genes that code for tumor-supressing proteins. In one case the mutations cause the "accelerator to stick at full speed," and in the other they cause the "brakes to fail."

Benign tumors are encapsulated, are similar to normal cells in tissue, and don't shed cells. Malignant tumors aren't encapsulated, are quite different from normal tissue cells, and do shed cells (metastases). Tumors in muscle, connective tissue, or bone are called sarcomas. Those in skin and other epithelial tissue are called carcinomas.

The first step in classification is to decide what living organism are. Briefly, they have the ability to function independently. They have cellular organization, they metabolize food, they have a genetic system, and they reproduce. Are virus organisms? They do not function independently, they are infectious particles rather than cells, and they can only replicate themselves within host cells. They are not much more than a fragment of nucleic acid, either DNA or RNA. They can evolve and exchange DNA or RNA. A prion (the culprit in "mad cow disease") is an infectious protein particle and lacks nucleic acid; it can trigger a chain reaction to increase its kind. So neither virus nor prions are life as it is defined by biologists.

All living organisms can be divided into two classes based on their cell types: prokaryotes and eukaryotes. Both have cells containing cytoplasm and ribosomes, which have RNA and translate RNA into proteins. Prokaryotes were the first forms of life and appeared about 3.5 billion years ago. They are single cells and do not contain nuclei or other membrane bound structures. Their DNA is not enclosed in chromosomes.

Eukaryotes appeared about 1.4 million years ago apparently when some bacteria invaded other bacteria and made themselves at home and became organelles in host cells, which then became eukaryotic cells. They are cells having a nucleus (which contains DNA within chromosomes), and they contain other membrane bound organelles that have specialized functions. Energy-producing organelles include mitochondria, which convert energy in food, and the remarkable chloroplasts in plants that carry on photosynthesis using the energy of the sun to convert carbon dioxide and water into carbohydrates and oxygen.

Early on people tried to make sense of the great diversity of life. They gave cumbersome names to species. In the 1750s Carolus Linnaeus, a Swedish biologist, introduced the system of naming the species with a two-part latinized name such as Homo sapiens, which specifies the genus and the species. This is comparable to a person's name such as Brown, John. Species are a group of animals with similar anatomical features and the ability to interbreed.

It is useful to group species into higher and higher categories. In 1977 Woese et al. proposed and many biologists have agreed on six kingdoms: 1) bacteria, 2) archaebacteria (also prokaryotes), 3) protists (a catch-all group), 4) fungi, 5) plants, and 6) animals. Other biologists lump bacteria and archaebacteria together resulting in five kingdoms. Here are the categories classifying man: species - sapiens, genus - Homo, family - hominidae (hominids), order - primates, class - mammalia, phylum - chordata (have backbones of some kind), and kingdon - animalia.

Originally the higher categories of classification were based mainly on anatomical similarities and differences. Evolution accounts for biodiversity, and the record can be inferred from changes in the genomes (the organisms' full sequences of As, Ts, Cs, and Gs).

How do we account for the great diversity exemplified by millions of species in six kingdoms of organisms? In the 18th Century, biology in the West supported the idea of "natural theology," which sought to find God's plan by studying nature. It was commonly thought that each species was a separate creation.

Charles Darwin first studied to become a surgeon but couldn't stand seeing the blood and gore and hearing the screams of uncontrolled pain from patients. He went to Cambridge and studied to become a minister. Many of the clergy were naturalists embracing natural theology. After graduation he got the opportunity to take the voyage on the Beagle in 1831 to keep Captain FitzRoy company. However, Darwin took it upon himself to observe and collect specimens. (The ship's doctor was the official naturalist on board.)

Darwin found 13 species of finches on the Galapagos Islands occupying different habitats. There were seed eaters, insect eaters, bud eaters, and cactus eaters. The size and shape of their bills varied according to their diet. This observation and others raised lots of questions in Darwin's mind, but it wasn't until he returned to England and started thinking about the significance of his findings that he began to formulate his theory of evolution.

Evolution needs time, lots of time, but it was generally thought that the Earth was young. While on board the Beagle, Darwin read Charles Lyell's book, Principles of Geology (1830), that proposed that the Earth was old and constantly changing. This had a big influence on Darwin's thinking. He was also influenced by Thomas Malthus' An Essay on the Principle of Population (1798) in which he observed that populations of plants and animals tend to increase geometrically.

In 1844 Darwin wrote and circulated an essay on the origin of the species and natural selection, but he didn't publish it. To his dismay, in 1858 he received a manuscript from Alfred Wallace covering the same subject and asking him to evaluate it and to forward it for publication, which Darwin did. Darwin then got busy and finished The Origin of the Species for publication in 1859. Western culture at that time was dominated by the Genesis model of creation. It's not hard to see why the shy Darwin was slow to publish his bomb shell.

Bear in mind that Darwin wrote his book before Mendel discovered the basic principles of inheritance and over a century before the dawn of molecular genetics. He could only compare the anatomy of different species. Now we can compare their chemistry, and we find amazing information that would have given him a lot more grist for his mill.

Evolution is not something that just took place in the distant past. It is going on right now, and one example is the evolution of bacteria to become drug resistant. They quickly evolve and adapt to new antibiotics. The overuse of antibiotics has contributed to the problem. I am afraid that I have contributed to this process by routinely using disinfectant hand soap. Some bacteria adapt to the disinfectant, and then when we really need the disinfectant, the bugs are resistant to it.

I rate "biological literacy" high in relation to other areas of learning. We are a mammal governed by the important biological principles. Furthermore, we read and hear so much about biological developments that it is important to have a basic knowledge of biology. The clincher is that it is interesting!