Genetics

The genetic code directs our biological functions — yours and mine and Bitsy (the dog) and Buttermilk Pie (the cat). Every new cell of an organism receives a copy of its own code of life, and then it uses the code to direct the proteins that do all the work of the cells, as we have described, by specifying the functional shape of each protein and producing them when and where they are needed in our bodies. Just for one example, this process makes available all the proteins required to do cellular respiration and so provides the energy that the cell needs to do all these tasks.

The more you think about all the tasks a cell and a body must do to stay alive, the more you recognize cycles inside cycles connected with other cycles. This is why life only comes from other life. When any one of these cycles is broken it not only stops its own task, but also all the other tasks that rely upon it for their functions. For example, the processes of mitosis, meiosis, DNA replication, cell division, all require organic energy that is made available by the process of cellular respiration, and cellular respiration would be impossible without all mitosis, meiosis, etc.

And the purpose of this one individual life seems to be meiosis and the fertilization of an egg by a sperm, a zygote, that will require proteins and energy to grow into an adult to repeat the cycle. These cycles more or less describe the flow of energy through the individual organisms. Even more elegant is the way in which they also participate in the flow of information through the entire living ecosystem.

Because of the processes of meiosis and cellular respiration, each new zygote is unique. It is correct for its species. For example, the new mouse cell contains 20 different kinds of chromosomes, two of each kind, two complete sets of chromosomes. Each kind of chromosome (numbered 1 through 20) contains the correct kinds of genes. For example there is a gene named tyrosinase in about the same position on every chromosome number one of the mouse. So every mouse has two tyrosinase genes. One came from the mother on chromosome number one and the other from the father on his chromosome number one.

However, the new zygote has a different genetic code than either the mother or the father, first because the chromosomes were assorted during the first division cycle of meiosis, and second because all of the genes (though they are of the same kind) are not identical to each other. The tyrosinase gene, for example, is responsible for making pigment in the pigment cells of mammals. It can be normal or it can be abnormal. If it is normal it does its function correctly; otherwise not. If the zygote gets two abnormal tyrosinase genes (one from each parent) then it will not have any normal gene to do the job of making pigment in the pigment cells. Of course, a zygote is not a baby. It is only one cell. However, that cell will make copies of itself until over time there are millions of cells until eventually some of the new cells will become pigment cells.

The genetic code is programmed to make tyrosinase in pigment cells. If the pigment cell is not able to make tyrosinase, then the new mammal will be an albino. If it is able to make tyrosinase, then it will have normal pigmentation. This is an example of just one kind of gene that is found in one location on one kind of chromosome. Similar relationships are possible for any kind of gene on any of the chromosomes. The function of meiosis is to reassort the genes. The function of fertilization is to make new combinations. Every individual zygote is therefore unique. Through all of time, every new generation of every sexually reproducing species consists of individual organisms that are not identical to each other. Every different phenotype is therefore also unique.

The phenotype is the physical nature of the body that results when a gene does its function. For example, the genotype of a normal tyrosinase gene could be referred to as Tyr+. The genotype of an abnormal tyrosinase gene could be referred to as Tyr – . Of course we already know that organisms have two of each kind of gene, so if a person, for example, has two normal tyrosinase genes, then we could write the person’s genotype as Tyr +/Tyr +. That person would make pigment in her pigment cells.

The function of the tyrosinase gene is to make the tyrosinase protein that causes the pigment cell to have pigment. That is, a pigmented phenotype. So the person has a pigmented phenotype.

If we want to refer to all the genes in one person, we use the term genome. If we want to refer to the entire phenotype of a person we could use the term phenome. Most people do not use this term, but I need it for the remaining part of our discussion because the phenomes of organisms, the variability of the phenomes, basically are the source of information flow for the entire ecosystem. They are the code of life of the ecosystem, as we will discuss later. Meantime, this discussion has become sufficiently complicated for today.

To sum up, living things can respond over time to conditions inside their bodies and outside their bodies. If they can not respond to conditions they do not stay alive. It’s not possible to respond to anything unless there is information flow (communication of some sort) between the conditions (cold temperature for example) and the response (putting on a coat). This is even more true of the automatic responses, for example, digesting your food. The ecosystem, to stay alive, also requires information flow. Information flow in individual organisms is a result of the genotypes of their cells. Information flow in the whole ecosystem is the result of the many different ways in which organisms interact with each other at the level of the phenome.

And that is the end of the story of information flow within organisms (genetics) and the beginning of the story of information flow across all the levels of organization of the ecosystem (evolution). Whew!

And don’t forget that every bit of this story requires organic energy or it does not happen.