We explain what genetics is, what its history is and why it is so important. Also, what is human genetics and genetic inheritance.
What is genetics?
Genetics is a branch of biology that studies how physical characteristics and traits are passed from one generation to another. To understand this inheritance, examine the genes found in the body’s cells that have a special code called DNA (deoxyribonucleic acid). This code determines the physical appearance and the chances of contracting certain diseases.
Genes function as information storage units and they contain instructions on how cells must function to make proteins. These proteins are what give rise to all the characteristics of the individual. DNA is a protein that controls the structure and function of each cell and has the ability to create exact copies of itself. RNA (ribonucleic acid) is a molecule that acts as a messenger for DNA information.
History of genetics
Genetics is a 20th century science (named for William Bateson in 1906) that began with the rediscovery of “Mendel’s laws.” 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 underwent a process of gradual descent, with certain modifications.
- 1865. The Czech Gregor Mendel, today considered the founder of genetics, established “Mendel’s laws” which consisted of the first basic rules on the transmission of patterns by inheritance, from parents to their children. In those days his work was ignored.
- 1900-1940. Period of “classical genetics”. Genetics emerged as its own independent science with the rediscovery of “Mendel’s laws.”
- 1909. The Danish Wilhem Johannsen introduced the term “gene” to refer to hereditary factors in Mendel’s research.
- 1910. Thomas Hunt Morgan and his group at Columbia University discovered the basis of the chromosomes found in every cell.
- 1913. Alfred Sturtevant sketched the first genetic map showing the location of genes, among other important characteristics.
- 1930. It was confirmed that hereditary factors (or genes) are the basic unit of inheritance both functional and structural and that they are located on the chromosomes.
- 1940-1969. DNA protein was recognized as the genetic substance and RNA as the messenger molecule for genetic information. Knowledge of the structure and functions of chromosomes was also advanced.
- 1970-1981. During this period the first DNA manipulation techniques emerged and the first artificially conceived mice and flies were achieved by genetic engineering with a mixture of DNA 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 mammal cloned from mammary cells. It was Dolly the sheep, who was not born from the union of two cells (an egg and a sperm) 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 for biology, health and society.
Importance of genetics
Genetics is a science that studies the transmission of hereditary characteristics of an organism, and its trajectory shows that it is a science of exponential growth. His contributions on the evolution of species and on providing solutions to congenital problems or diseases are his 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.
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. Human beings arise from the union of two cells, an egg and a sperm, which form a new cell called a “zygote” that divides successively to form a baby with all its features and characteristics.
The human being has about 30,000 genes They contain the instructions that determine the growth, development and functioning of the organism. Genes are found on 23 pairs of chromosomes (or 46 chromosomes in all) within cells. Chromosomes are structures that contain DNA and RNA, that is, they have a sequence of chemical information that determines what the morphology and functioning of the organism will be like.
Genetic heritage
Genetic inheritance is transmission, through the information existing in the nucleus of cells, from the anatomical, physiological or other characteristics, from a living being to its descendants. 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:
- Genotype. It is the set of all the transmissible information that genes contain.
- Phenotype It is any visible characteristic that an individual presents (physical or behavioral) determined by the interaction between the genotype and the environment.
- Meiosis It is one of the forms of cell division of cells
reproductive, in which there is a union or zygote of two cells (an egg and a sperm). - Mitosis. It is the cell division that results in two new cells with the same number 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 mutations, which take place in DNA.
Types of genetic inheritance
There are different types of genetic inheritance that depend on discrete units called “genes.” Humans have 23 pairs of chromosomes, a pair from the mother, and another pair, from the father. Chromosomes are structures that contain genes and where different forms of the same gene can exist, which are called “alleles”.
For example, in the eye color gene, an individual can inherit one 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 individual’s eye color will depend on the combination of alleles of the same gene. From this example, the different types of genetic inheritance that follow will be better understood.
- The dominant-recessive inheritance. It occurs when one of the alleles dominates over another and its traits are dominant.
- Incomplete dominant inheritance. It occurs when neither allele dominates the other, so the trait in the offspring is a mixture of both alleles.
- Polygenetic 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, height.
- The inheritance linked to sex. It occurs when the alleles are found on the sex chromosomes (they correspond to pair number 23), which are represented by the sign “XY” in males and “XX” in females. Men can only pass their Y chromosome to their male children, so no X-linked traits are inherited from the father. Conversely, it occurs with the mother who only passes her X chromosome to her female daughters.
Genetic variability
Genetic variability is the modification of the genes of individuals of the same species that they differ according to the population in which they live. For example, the jaguars that inhabit Brazil are almost twice the size of 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 chemical substances in the environment.
- The combination of genes. It is generated during the reproduction of cells and is how most hereditary variations occur.
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 modifying the hereditary 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.”