whatarechromosmesandgenes

What are chromosomes and genes?
By Manuel Luciano da Silva, Medical Doctor
July 26 205

I want this series of articles dealing with the study of DNA concerning the possibility of the Portuguese nationality of the navigator Cristóvão Colon or Christopher Columbus, to be understood even by those persons that did not have the opportunity to acquire advanced or medical education. This is the reason why I consider it necessary that my readers understand very well what are chromosomes and genes so they will be able to comprehend the specific study of Y chromosome and also of mitochondria. (composed of two Greek words Mito = ‘thread like’ + chondrion = ‘rod-shaped components’).

Chromosome is a name composed by two Greek words: chromo = color , plus soma = body. For us to better understand the meaning of chromosome we have to analyze the composition of a cell. The best example of a cell is a chicken egg which has three parts: (1) the shell or membrane; (2) the white of the egg or cytoplasm; and (3) the yolk or the yellow of the egg. The chromosomes of the chicken are in the yolk or the yellow of the egg. The chromosomes are the substances that transmit from one generation to the other the characteristics of the chicken if the chicks are going to be red, white or even black.

In each species of animals or vegetables the number of chromosomes is constant. The human race has 46 chromosomes, salamander 24, fruit fly possesses 8, round worms 4 and the three varieties of wheat can have 14, 28 or 42 chromosomes and the corn 20 chromosomes.

Under the microscope the chromosomes appear to be filaments of threads of molecules of deoxyribonucleic acid, which is represented by this sigla (DNA), which is the unit of life.

The 46 human chromosomes are numbered according to their size and shape. Thus the larger chromosomes are the ones that are numbered in the first places and therefore have the lowest numerals. The human chromosomes are organized in pairs. This way, the pair chromosome number one is the largest and henceforth. The pair with two smallest chromosomes is number 23, which are called also the sexual chromosomes! In male this pair of chromosomes is represented by the letters X and Y. In the woman the sexual pair consists of two letters XX.

Here you have a diagram with all the 23 human chromosomes, which is a total of 46 chromosomes.

Each chromosome has about 500 to a 1000 genes. Genes are specific factors which determine the color of our skin, the color of our eyes, etc. Each gene has an genetic function in each human individual. There are genes called dominant and others called recessive. The dominant transmit the same qualities to the following generations. The recessive continue as if they “are a sleep” and only reveal their characteristics if both parents give one recessive gene to compose the same pair. Then together they will attain a dominant genetic force.

To make this explanation even simpler, we are going to compare the chromosomes and genes with a pine tree with 23 pairs of branches.

The branches of the pine tree will represent the total of 46 chromosomes, making therefore 23 pairs, and the leaves of the pine tree or pine needles will represent the genes which can be in number from 500 to 1000.

This photo or a pine tree shows us 23 pairs of branches with a total of 46 chromosomes. Each branch or chromosome has the genes or pine needles, which can be anywhere from 500 to 1000 genes. Please note that on the very top of the opine tree exists the sexual pair for a man XY.

The branches of the lower part of the pine tree represent the larger chromosomes and therefore they have the lower numbers.

Medical science has already discovered that for example the Joseph-Machado’s disease has a defect on chromosome number 14. What the medical science needs is to find which genes, or which pine needles are missing among the 500 to 1000 so they can be repaired. Indeed this is the biggest medical challenge to be able to substitute the pine needles or the respective genes in the proper chromosome to correct the hereditary disease.

DNA is a sigla composed by the initials of the following names: Desoxyribo Nuclei Acid.

This acid is considered the UNIT OF LIFE. It was discovered in 1953 by two scientists, one American James Watson and the other an Englishman Francis Crick. Both received the Nobel Prize for this scientific discovery.

Dr. James Watson and Dr. Francis Crick with the three dimension molecule of the DNA that they conceived in 1953.


Here is the diagram of the DNA molecule seen by the microscope.	The DNA drawing with its helical form

If we pay close attention to the molecule of DNA we will verify that it looks like a regular ladder with two dorsal spines and several steps, but that has been rotated in a helix.

Another thing we should note is that the various steps of the ladder are formed by “different pieces of wood”, or four different substances called BASES with the following g names:

The Anglo-Saxon alphabet has 25 letters to make a million different words. The Portuguese alphabet has 22 letters because it does not use the letters K, W and Y to make also a million words.

But Mother Nature uses only four letters AGTC and is able to make and maintain so many millions if not billions of beings on this earth, such as animals, vegetables and virus. It is indeed phenomenal!

In the human race the Y chromosome is the smallest and the most powerful. It is the Y chromosome that determines the masculine sex. But this Y chromosome has another unique and very important characteristic: it NEVER changes from one generation to the other if it is transmitted directly from father to son. It maintains the same genes for thousands of years! This is the reason why the DNA studies can be done in old bones if the direct father-son has been kept is successive generations. The bones in mausoleums are good up to one hundred thousand years for the DNA testing!

Here is a diagram of Y chromosome. Please note that the horizontal lines have different width. They are the different genes. Note also that some genes are colored. This is the reason why the name Chromosome.

Mitochondria are located usually in the white of the egg, or in the cytoplasm. The white of the egg is where the energy lies so that the chick can grow and come out of the shell in 21 days. It is in the white of the egg or the in the cytoplasm of every cell that all the energy mechanisms of the cell are located. The mitochondria, which are pieces of DNA, function as if they are electrical motors, producing all the phosphoric energy for the cells to live.

99% of mitochondria only give genetic information about the mother. In the chicken egg the yolk does not have any mitochondria because the very few mitochondria that the sperm has at the same time that fuses into the egg to fertilize it, it looses its few male mitochondria. Usually a regular cytoplasm human cell contains anywhere from 500 to 1000 mitochondria. At first sight it seem very easily to use mitochondria to do DNA diagnosis, but this is not the case, because there is a tremendous variety of combinations among the mitochondria which makes the genetic diagnosis very difficult, if not impossible. This is the very reason why the DNA diagnosis is much easier in men. Because the Y chromosome is constant, never changes from generation to generation. One condition is required: the transmission has to be from father-son directly all the time. We know that women change very easily… including even in their mitochondria!...

Because of the reasons explained above, Professor Francisco Corte Real and his scientific team want to start their diagnosis by using the Y chromosome of males. They will try first to examine the old bones in the mausoleums of the Dynasty of Avis, of Dynasty of the House of Bragança, the Dynasty of the Dukes of Verágua, from Spain or even start with saliva of the live members of these families.

These tests are indeed a big challenge to the scientists and we wish them the greatest success. The entire world will be waiting their results, either positive or negative.