Genetics

We explain what genetics is, what its history is and why it is so important. Also, what is human genetics and the types of genetics.

What is genetics?

Genetics is the study of physical characteristics and traits passed from one generation to another. Although humans have always been interested in the modes of inheritance of living beings, genetics is considered a science of the 20th century.

Mendel's laws, the study of chromosomes and the deciphering of the structure of DNA marked great foundations in contemporary genetics.

At the moment, Advances in computing opened a large field of research in human genetics especially when it comes to hereditary diseases. Other activities, such as agriculture and livestock, also use the contributions of genetics to improve their production.

One of the most important aspects of genetics is the ability to predict the characteristics that are transmitted to the next generation. The Classical Mendelian inheritance patterns They describe the different types of inheritance that are known and allow us to predict the behavior of hereditary traits.

The fact that there are differences between individuals of the same species is known as genetic variability and is the genetic basis of the main evolutionary theories.

Currently, genetics has been the target of numerous investigations to be able to make modifications to genes artificially. This is known as genetic manipulation.

• See also: Genetic code

Keys to understanding genetics

To understand the main fundamentals of genetics it is necessary to master some key concepts. These concepts include the distinction between chromosomes, genes and alleles, the differentiation between genotype and phenotype, the different forms of cell division (mitosis and meiosis) and the notion of mutation.

• Alleles. They are alternative variants for the same gene. In diploid organisms, most genes have two alleles.
• Chromosome. It is a packaging unit of DNA. Sites are discriminated on chromosomes (loci) where the genes are found.
• gene. It is the minimum unit of information that can be heritable and, sometimes, it is possible to associate it with a visible characteristic.
• Genotype. It is the set of all the transmissible information contained in the genes.
• Phenotype. It is any visible characteristic that an individual presents (physical or behavioral) determined by the interaction between genotype and the environment.
• 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.
• Meiosis. It is one of the forms of cell division typical of reproductive cells, in which a union or zygote of two cells (an egg and a sperm) occurs.
• Mitosis. It is cell division that results in two new cells with the same number of chromosomes, that is, the same genetic information respectively.

human genetics

human genetics is responsible for studying the mechanisms of inheritance in human beings. This also includes studying cells, which are the small units that make up muscles, skin, blood, nerves, bones, organs and everything that makes up our body.

Inside our cells, genetic information is found, encoded in the DNA molecule (deoxyribonucleic acid). DNA is organized into structures called chromosomes in which the genes are found. Genes are discrete units of information, which can be transmitted through generations.

It is known that The human species has about 30,000 genes that determine the growth, development and functioning of our body. Genes are distributed on 23 pairs of chromosomes (in total, a person has 46 chromosomes).

How does genetic inheritance work?

Human beings, like many living beings, are diploid. This means that we have two complete sets of chromosomes. We have 46 chromosomes in total, distributed in 23 pairs. Each pair has one chromosome from the egg (typically provided by the mother), and one chromosome from the sperm (generally provided by the father).

Currently, chromosomes are known to contain genes (heritable units with specific information). There can be different forms of the same gene, called “alleles.” That is, alleles are the different inherited versions of the same gene. In general, in diploid organisms there are two alleles.

For example:

In the eye color gene, located on chromosome 15, a person can inherit an allele from the father that states that the eyes are blue. At the same time, the allele inherited from the mother may indicate that the eyes are green. Finally, the inherited characteristic will depend on the type of inheritance of that particular gene (or that small group of genes).

Thus, The behavior of alleles in the transmission of heritable traits can be classified according to different inheritance patterns. The most studied types of inheritance are known as Classic patterns of Mendelian inheritance.

Types of genetic inheritance

The different types of genetic inheritance are based on the behavior of the alleles (variants of the same gene) and how they are distributed on the chromosomes that we inherit from our parents. There are different types of inheritance, known as Mendelian classical inheritance patternsOh atypical inheritance patterns.

Mendelian inheritance patterns describe the types of inheritance of heritable characteristics. They are very useful for understanding characteristics that depend on the expression of a single gene.

Autosomal inheritance

Autosomal inheritance corresponds to genes that are on all chromosomes, except the sex chromosomes. Two autosomal inheritance patterns are described.

• Autosomal dominant pattern. It happens when one allele dominates over another. For a certain characteristic to be inherited, it is enough for the individual to have received the dominant allele from one of his or her parents. The other, if it is different, does not express itself, it remains silenced. For example, the “brown eyes” allele is dominant. If it is inherited, then the person will have brown eyes, even if their other allele has information for green or blue eyes.
• Autosomal recessive pattern . It happens in the absence of a dominant allele. For a certain characteristic to be inherited, it is necessary that the individual has received the recessive allele from both parents. For example, a person receives both “blue eyes” alleles (and none “brown eyes”). Then his eyes will inevitably be blue.

Sex-linked inheritance

Sex-linked inheritance describes the behavior of genes found on sex chromosomes (X or Y). Because females inherit two X chromosomes (XX) and males receive a single X chromosome and a Y chromosome (XY), particular patterns of sex-linked inheritance are described.

• X-linked dominant pattern. It happens when an allele is found on one X chromosome and also dominates another. For a certain characteristic to be inherited, it is enough for the individual to have received the dominant allele from one of his or her parents. This pattern is common in rare serious diseases, such as Alport Syndrome (a birth condition that includes kidney damage).
• X-linked recessive pattern. It happens in the absence of a dominant allele, on another X chromosome. Depending on whether the individual is male (XY) or female (XX), there are different conditions for a certain characteristic to be inherited. XX individuals need to inherit the same allele from both parents. In XY individuals, it is enough to have inherited the recessive allele on the only X chromosome they receive. For example, the allele that causes color blindness (alteration in distinguishing colors) is found on the X chromosome and has a recessive pattern. Men who inherit the altered allele are color blind. On the other hand, women need to inherit two copies of that allele to present color blindness.
• Y-linked inheritance. It happens in the genes found on the Y chromosome, which are very rare. For the characteristic to be inherited, it is enough for the individual to have received the only allele from the Y chromosome. The traits are transmitted by the parents to all their male offspring. For example, auricular hypertrichosis (ear hair) has this inheritance pattern.

In addition to the classic Mendelian inheritance patterns, genetics studies other types of inheritance, known as atypical patterns of inheritance. They include mitochondrial inheritance, co-dominance, incomplete dominance, and polygenetic or multifactorial inheritance.

• See also: Inheritance

Genetic variability

The genetic variability of a population is the set of variants that exist for the same gene, within individuals of the same population. For example, among human beings, there is genetic variability in eye color (they can be brown, black, light blue, etc.).

Among the organisms that make up a species, the vast majority of genes are the same. However, some may present slight variations (alleles), which make one individual different from the other, but not so different as to belong to another species. For example, The jaguars that live in Brazil are almost twice the size of those that live in Mexico even though they belong to the same species.

Population genetics is a discipline dedicated to the study of genetic variability. It has its foundations in the analysis of allele frequencies (proportions with which the different variants occur within a population). These observations are key to supporting the main evolutionary theories.

Causes of genetic variability

Genetic variability constitutes a great advantage in evolutionary terms. Species that have greater variability are more likely to survive in changing environments. There are two main sources of genetic variation: sexual reproduction and mutation.

• sexual reproduction. It is the form of reproduction that involves the combination of the genetic material of both parents. Sexual reproduction allows for more possibilities of allele combinations.
• Mutation. It is produced by any change in a DNA sequence, that is, it is a change in the genotype. It can occur due to an error in DNA replication (by chance) or due to environmental conditions that increase the rate of mutations (for example, radiation or different chemicals in the environment).

Genetic manipulation

Genetic manipulation, also called “genetic engineering,” focuses on the study of DNA with the goal of achieving targeted modifications.

It consists of a series of laboratory methods that allows you to isolate genes or DNA fragments clone them and introduce them into other organisms so that they express themselves.

For example, when new genes are introduced into plants or animals, the resulting organisms are called “transgenic.”

• Genetic manipulation

Importance of genetics

Genetics is a science that studies the transmission of the hereditary characteristics of an organism, from generation to generation. Important problems of great interest to human beings can be addressed from genetics.

• in medicine. Studies in human genetics are especially important when it comes to diseases that can be transmitted between generations.
• In the agricultural industry. Genetic analyzes and interventions become relevant to obtain crop varieties with characteristics of commercial interest.
• In the livestock industry. Genetics can help increase the production of certain animals in the food industry (cows, salmon, chickens). Also, with animals linked to sports practices (horses, bulls, dogs).
• In evolutionary biology. Genetic studies provide information at the population level.
• in the right. Many contributions from genetics serve to determine culprits in crimes and to clear up doubts regarding family relationships.

History of genetics

Although humans have always been interested in the inheritance of traits among living beings, genetics is considered a science of the 20th century. After the rediscovery of the ideas proposed by Mendel in 1865, genetics received great interest from American and British science, among others. Scientists such as Thomas Morgan, Alfred Sturtevant and Ronald Fisher made great contributions to studies on the organization of chromosomes.

In 1952, Rosalind Franklin obtained the first “photo” of DNA thanks to which James Watson and Francis Crick received the Nobel Prize in Physiology in 1962, for proposing the double helix structure. This advance allowed us to deepen our knowledge about genes, even testing cloning experiments.

Starting in the 1980s, genetics gained new momentum thanks to developments in the field of computing, as new technologies made it possible to sequence complete genomes. It gave rise to what is known today as genomics.

• 1858. Cell as a reproduction unit.
  The German Rudolf Virchow introduced the principle of continuity of life by cell division and established the cell as a reproduction unit.
• 1859. The origin of species, Darwin.
  The British Charles Darwin presented his theory of evolution in the book The origin of species. He postulated that current organisms come from beings that existed in the past and that went through a process of inheritance with modifications.
• 1865. Mendel's Laws .
  The Czech Gregor Mendel, today considered the founder of genetics, established the Mendel's laws, which consisted of the first basic rules about the transmission of patterns by inheritance, from parents to their children. At that time his work was ignored.
• 1900-1940. Classical genetics.
  During the period known as “classical genetics,” genetics emerged as its own and independent science with the rediscovery of the Mendel's laws.
• 1905. Definition of the term genetics .
  William Bateson, British biologist, defines the term Ggenetics.
• 1909. Definition of the term gene .
  The Danish Wilhem Johannsen introduced the term “gene” to refer to the hereditary factors of Mendel's research.
• 1910. Discovery of chromosomes.
  Thomas Hunt Morgan and his group at Columbia University discovered the basis of chromosomes found in every cell.
• 1913. First genetic map.
  Alfred Sturtevant sketched the first genetic map showing the location of genes, among other important features.
• 1930. Genes as a unit of inheritance.
  It was confirmed that hereditary factors (or genes) are the basic unit of both functional and structural inheritance and that they are located on the chromosomes.
• 1940-1969. DNA as a genetic substance.
  DNA was recognized as the genetic substance and RNA as the messenger molecule of genetic information. James Watson and Francis Crick deciphered the double helix structure of DNA.
• 1970-1981. First DNA manipulation techniques.
  During this period, the first DNA manipulation techniques emerged and the first mice and flies conceived artificially through genetic engineering were achieved.
• 1990. Human Genome Release.
  Lep-Chee Tsui, Francis Collins and John Riordan found the defective gene that, when mutated, is responsible for the hereditary disease called “cystic fibrosis.” The “human genome” project was launched.
• 1995-1996. First cloned mammal.
  Ian Wilmut and Keith Campell obtained the first cloned mammal (Dolly the sheep).
• 2001-2019. century of genetics.
  The human genome project was successfully completed. This result gave rise to a new era of genetic research, and the 21st century was called “the century of genetics.”

References

• Curtis H., Barnes N., Massarini A., Schnerck A., BIOLOGY. 7th Edition. Panamericana Medical Editorial (2008).
• De Robertis, E.Fundamentals of cellular and molecular biology. 4th Edition. El ateneo (2010).