Strictly speaking, I should have used the word "nucleosides" instead of "bases" but "bases" is easier to spell and approximately right. These refer to the four different chemicals, adenosine, guanosine, cytosine, and thymidine, whose sequence in the DNA chain codes the genetic information.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
If you look at a piece of skin, or liver, or any other body part under a microscope, you will see that instead of being a continuous sheet or blob of stuff, it is made of tiny blocks glued together. If you look at a slice through that material under the microscope, you will see that the blocks are not solid, rather they are more like boxes with a variety of contents. Each box will have a membrane, like a sheet of plastic only made of protein and lipids, that form the outer surface. There will be a large ball that seems to be full of wet string - that is the nucleus. There will be small capsule-shaped objects, anywhere from a few to a few thousand depending on the kind of cell. These are the mitochondria, that produce the energy the cell needs to live and function. There will be a maze of granular membranes going everywhere in the cell outside the nucleus - these are the microsomes, in which various chemical reactions take place as the cell does whatever that kind of cell is supposed to do. There will be many other odd little do-dads, but you get the idea. Those "wet strings" in the cell nucleus are the chromosomes that contain all your genetic information (instruction manual.)

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The "genetic code" has the sequence of bases, in threes, specifying which amino acid comes next in the protein molecule being defined by that particular gene.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
An enzyme is a protein that makes something happen. It is a biological catalyst (accelerator) that controls the speed of a chemical reaction in the body. Life is possible because enzymes make reactions occur in the body that increase the order (complexity, non-uniformity) of the system. The normal progression for non-living things is toward disorder (to dust and ash!)

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Each of your 30,000+ genes carries the instructions for the manufacture of one kind of protein, such as a particular enzyme, structural protein, transport protein, and so on. Each type of cell in your body (e.g. liver cell, skin cell, etc.) will have a different subset of the 30,000+ genes turned on - that's what makes the different cells different.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Proteins are polymers like DNA, except that they are made of amino acids instead of nucleic acids, and there are 21 different amino acids that may be used in making the polymer. Proteins provide the structure of the body and do its work (for example, muscle contraction proteins, enzymes that digest your food, etc.)

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Genealogy is the study of genetic relationships between people.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Genetics is the study of gene-controlled relationships inside a person.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Males produce spermatozoa (sperm for short), and release about 1-15 billion of them in a given ejaculation. Females produce ova, eggs for not as short, and release one a month. One spermatozoan and one ovum (singular forms of the nouns), the germ cells, merge to produce a complete, single cell that will develop into a baby. Human germ cells only contain 23 chromosomes each.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Mutations occur when the sequence of bases in a gene is changed and that change occurs in the germ cells. The sequence may change because one base is replaced by another, a base gets deleted, or a base becomes chemically modified. The ultimate cause may be exposure to radiation, exposure to chemicals called mutagens (which may also be carcinogens if the mutaion causes cancer), some viruses, or age-related mistakes in reproducing the DNA as cells divide.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The effect of a gene is said to be dominant if it occurs regardless of the nature of the other copy of that gene. If both members of a pair of genes have to be alike in order for the effect to occur, it is said to be a "recessive" gene.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Identical twins occur when the original cell formed by the merging of sperm and egg divides and the resulting two cells separate, each then developing into a new baby. If instead a woman happened to release two ova at the same time and both were "fertilized" (merged with sperm), two non-identical (fraternal) twins will result.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A given gene may be blocked from functioning (turned off) or unblocked (turned on). If it is "on" and functioning, it is said to be "active" or "activated".

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Incest is sexual intercorse between persons so closely related that marriage between them is forbidden by law or cultural taboo. Particular religious denominations may forbid marriage between persons less closely related than the law forbids in some cases.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Siblings are children of the same parents. Half-siblings share a single parent. Marriage between either is forbidden by law in most places.