What is genetics?

We explain what genetics is, what its history is and why it is so important. In addition, what is human genetics and genetic inheritance.

1. What is genetics?

Genetics is a branch of biology that studies how physical characteristics and traits are transmitted from one generation to another . To understand this inheritance, examine the genes found in the body’s cells and that have a special code called DNA (deoxyribonucleic acid). This code determines the physical appearance and the probability of contracting certain diseases.

Genes function as storage units and contain instructions on how cells must function to form proteins . These proteins are what give rise to all the characteristics of the individual. DNA is a protein that controls the structure and functioning of each cell and has the ability to create exact copies of itself. The RNA (ribonucleic acid) is a molecule that performs the function of messenger DNA information.

2. History of genetics

Genetics is a science of the twentieth century (named in 1906 by William Bateson) that began with the rediscovery of the “laws of Mendel.” Certain conceptual advances of the 19th century were key to later genetic thinking, for example:

• 1858. The German Rudolf Virchow introduced the principle of continuity of life by cell division and established the cell as a unit of reproduction.
• 1859. The British Charles Darwin presented his theory “The Origin of Species”, in which he maintains that existing organisms come from beings that existed in the past and that went through a process of gradual descent, with certain modifications.
• 1865. The Czech Gregor Mendel, today considered the founder of genetics, established the “Mendel laws” which consisted of the first basic rules on the transmission of inheritance patterns, from parents to their children. In those times his work was ignored.
• 1900-1940. period of “classical genetics”. Genetics emerged as their own independent science with the rediscovery of the “laws of Mendel.”
• 1909. The Danish Wilhem Johannsen introduced the term “gene” to refer to the hereditary factors of Mendel’s investigations.
• 1910. Thomas Hunt Morgan and his group at Columbia University discovered the basis of the chromosomes found in each cell.
• 1913. Alfred Sturtevant outlined the first genetic map showing the location of genes, among other important features.
• 1930. It was confirmed that hereditary factors (or genes) are the basic unit of both functional and structural inheritance and that they are located on chromosomes.
• 1940-1969. The DNA protein was recognized as the genetic substance and RNA as the messenger molecule of genetic information. Progress was also made in the knowledge of the structure and functions of chromosomes.
• 1970-1981. During this period the first DNA manipulation techniques emerged and the first artificially conceived mice and flies were obtained by genetic engineering with DNA mixing from other organisms.
• 1990. Lep-Chee Tsui, Francis Collins and John Riordan found the defective gene that, when mutated, is responsible for the inherited disease called “cystic fibrosis.” James Watson and Francis Crick, along with other collaborators, launched the “human genome” project and discovered the double helix structure of the DNA molecule.
• 1995-1996. During the years of the scientific and social revolution, Ian Wilmut and Keith Campell managed to capture the complete sequence of a genome and obtained the first cloned mammal from mammary cells. It was the Dolly sheep, who was not born from the union of two cells (an egg and a sperm cell) but came from a mammary glandular cell of another sheep that was no longer alive.
• 2001-2019. During this period, considered the “century of genetics”, the human genome project was successfully completed and reached 99% of the sequenced genome. This result gave rise to a new era of genetic research that offered relevant contributions to biology, health and society .

3. Importance of genetics

Genetics is a science that studies the transmission of the inherited characteristics of an organism , and its trajectory shows that it is a science of exponential growth. Their contributions on the evolution of the species and on giving solutions to congenital problems or diseases are their greatest advantage despite the fact that some experiments go hand in hand with controversies at an ethical and philosophical level, such as the cloning of animals.

4. Human genetics

Human genetics examines biological inheritance in humans through cells that are small living units that make up muscles, skin, blood, nerves, bones, organs and everything that makes up an organism . The humans arising from the union of two cells, an egg and a sperm, forming a new cell called “zygote” which is divided successively to form a baby with all its features and characteristics.

The human being has about 30,000 genes that contain the instructions that determine the growth, development and functioning of the organism. The genes are distributed in 23 pairs of chromosomes (or 46 chromosomes in total) within the cells. Chromosomes are structures that contain DNA and RNA, that is, they have a sequence of chemical information that determines how the morphology and functioning of the organism will be.

5. Genetic heritage

The genetic inheritance is the transmission, through the existing information in the nucleus of the cells , of the anatomical, physiological or other characteristics, of a living being to its descendants. In order to know the genetic inheritance, the origin of the similarities between the members of the same family is not enough, but it is necessary to contemplate the genetic epidemiology (diseases of the ancestors) and the environment in which an individual interacts. The transmission of genetic material has the following characteristics:

• Genotyped . It is the set of all the transmissible information that genes contain.
• Phenotype It is any visible characteristic presented by an individual (physical or behavioral) determined by the interaction between the genotype and the environment.
• Meiosis . It is one of the forms of cell division typical of
  reproductivecells, in which a union or zygote of two cells (an ovule and a sperm cell) occurs.
• Mitosis . It is the cell division that results in two new cells with the same amount of chromosomes, that is, the same genetic information respectively.
• Mutation . It is the variation that occurs in the genotype of an individual and can be spontaneous or induced by genetic muta agents, which take place in the DNA.

6. Types of genetic inheritance

There are different types of genetic inheritance that depend on discrete units called “genes.” Humans have 23 pairs of chromosomes , one from the mother, and another from the father. Chromosomes are structures that contain genes and where there may be different forms of the same gene called “alleles.”

For example, in the eye color gene , an individual may inherit an allele from the father that determines that the eyes are blue and inherit a different one from the mother that indicates that the eyes are green. Therefore, the eye color of the individual will depend on the combination of alleles of the same gene . From this example, you can better understand the different types of genetic inheritance that are developed below.

• The dominant-recessive inheritance. It occurs when one of the alleles dominates over another and its features are dominant.
• The incomplete dominant inheritance. It occurs when neither of the alleles dominates the other, so the trait in the offspring is a mixture of both alleles.
• The poly genetic inheritance. It happens when an individual characteristic is controlled by two or more pairs of genes and is expressed in the form of small differences. For example, the height.
• The inheritance linked to sex. It occurs when the alleles are in the sex chromosomes (they correspond to the pair number 23), which are represented by the sign “XY” in the male and “XX” in the female. Men can only pass their Y chromosome to their male children, so no X-linked trait is inherited from the father. Conversely, it happens with the mother who only passes her X chromosome to her female daughters.

7. Genetic variability

Genetic variability is the modification of the genes of individuals of the same species that differ according to the population in which they live . For example, jaguars that inhabit Brazil are almost twice as large as those that inhabit Mexico, even though they belong to the same species. There are two main sources of genetic variation:

• The mutation It is produced by any change in a DNA sequence, both by an error in DNA replication and by radiation or environmental chemicals.
• The combination of genes. It is generated during the reproduction of cells and is how most inherited variations occur.

8. Genetic manipulation

Genetic manipulation, or also called “genetic engineering”, focuses on the study of DNA in order to achieve its manipulation . It consists of a series of laboratory methods that allow you to modify the inherited characteristics of an organism to isolate genes or DNA fragments, clone them and introduce them into other genomes so that they are expressed. For example, when new genes are introduced into plants or animals, the resulting organisms are called “transgenic.”