Genetics

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Genetics

Genetics is the study of physical characteristics and traits that are passed down from one generation to the next. It is the study of inheritance, the process by which a parent passes certain genes on to their children. A person's appearance (height, hair, skin, and eye color) is influenced by genes. Other characteristics influenced by inheritance could include the likelihood of contracting certain diseases, mental abilities, or natural talents.

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

One of the most important aspects of genetics is the ability to predict the characteristics that will be passed down to the next generation. Classical Mendelian inheritance patterns describe the different types of inheritance 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.

Concepts to better understand genetics

Alleles: These are alternative variants of the same gene. In diploid organisms, most genes have two alleles.

Chromosomes: These are the packaging units of DNA. Chromosomes distinguish sites (loci) where genes are located.

Gene: It is the smallest unit of information that can be inherited 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 the 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 mutation 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).

Mitosis is the cell division that results in two new cells with the same number of chromosomes, that is, the same genetic information respectively.

Humans have cells with 46 chromosomes. These consist of two chromosomes that determine their sex (X and Y chromosomes) and 22 pairs of non-sex (autosomal) chromosomes. Males have "46,XY" and females have "46,XX." Chromosomes are made up of strands of genetic information called DNA. Each chromosome contains sections of DNA called genes. These genes carry the information needed for your body to make certain proteins.

Each pair of chromosomes contains one chromosome from the mother and one from the father. Each chromosome in a pair carries basically the same information; that is, each pair has the same genes. Sometimes, there are slight variations in these genes. These variations occur in less than 1% of the DNA sequence. Genes that have these variations are called alleles.

Some of these variations can cause a gene to not work properly. A variant gene can lead to an abnormal protein or an abnormal amount of a normal protein. In an autosomal chromosome pair, there are two copies of each gene, one from each parent. If one of these genes is a variant, the other may produce enough protein so that no disease develops. When this happens, the abnormal gene is called recessive. Recessive genes are said to be inherited either in an autosomal recessive or X-linked pattern. If two copies of the variant gene are present, the disease may develop.

However, if only one variant gene is needed to cause the disease, this leads to a dominantly inherited condition. In a dominant condition, if a variant gene is inherited from either the mother or the father, the child will likely develop the disease.

A person with a variant gene is called heterozygous for that gene. If a child receives a variant gene for a recessive disease from both parents, they will develop the disease and be homozygous (or compound heterozygous) for that gene.

For example, in the eye color gene, located on chromosome 15, a person can inherit an allele from the father that determines blue eyes. At the same time, the allele inherited from the mother may determine green eyes. Ultimately, the inherited characteristic will depend on the type of inheritance of that particular gene (or small group of genes).

Types of Genetic Inheritance

The different types of genetic inheritance are based on the behavior of alleles (variants of the same gene) and how they are distributed on the chromosomes we inherit from our parents. There are different types of inheritance, known as classical Mendelian inheritance patterns and 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 present on all chromosomes, except the sex chromosomes. Two patterns of autosomal inheritance are described.

Autosomal Dominant Pattern: This occurs 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 their parents. The other allele, if different, is not expressed and is silenced. For example, the "brown eyes" allele is dominant. If it's inherited, then the person will have brown eyes, even if their other allele has information for green or blue eyes.

Autosomal recessive pattern: Occurs in the absence of a dominant allele. For a certain characteristic to be inherited, the individual must have received the recessive allele from both parents. For example, a person receives both "blue eyes" alleles (and none for "brown eyes"). Then their eyes will inevitably be blue.

Sex-linked inheritance

Sex-linked inheritance describes the behavior of genes found on sex chromosomes (X or Y). Because women inherit two X chromosomes (XX) and men receive only one X and one Y chromosome (XY), the following sex-linked patterns exist.

X-linked dominant pattern: This occurs when an allele is found on an X chromosome and also 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 their parents. This pattern is common in rare, serious diseases, such as Alport syndrome (a birth condition that involves kidney damage).

X-linked recessive pattern: This occurs 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 single X chromosome they receive. For example, the allele that causes color blindness (an impairment in distinguishing colors) is located on the X chromosome and has a recessive pattern. Men who inherit the altered allele are colorblind. In contrast, women need to inherit two copies of that allele to develop color blindness.

Y-linked inheritance: This occurs in 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 single allele from the Y chromosome. The traits are passed on by parents to all their male offspring. For example, auricular hypertrichosis (hair in the ears) has this inheritance pattern.

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 humans, 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 have slight variations (alleles), which make one individual different from another, but not enough to belong to another species. For example, 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 is based on the analysis of allele frequencies (the proportions at which different variants occur within a population). These observations are key to the foundation of major evolutionary theories.

Causes of Genetic Variability

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

Sexual Reproduction: This is the form of reproduction that involves combining the genetic material of both parents. Sexual reproduction allows for more possibilities for allele combinations.

Mutation: This is caused 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 mutation rate (for example, radiation or various chemicals in the environment).

Genetic Manipulation

Genetic manipulation, also called "genetic engineering," focuses on the study of DNA with the goal of making targeted modifications to an organism's DNA.

It consists of a series of laboratory methods that allow genes or DNA fragments to be isolated, cloned, and introduced into other organisms for expression.

For example, when new genes are introduced into plants or animals, the resulting organisms are called "GMOs."

If you would like to learn more about genetic manipulation (types, advantages, disadvantages, legal aspects), we recommend visiting the following link: https://concepto.de/manipulacion-genetica/

Importance of Genetics

Genetics is a science that studies the transmission of an organism's hereditary traits from generation to generation. Genetics can address important problems of great interest to humans.

In medicine, human genetics studies are especially important when dealing with diseases that can be transmitted between generations.

In the agricultural industry, genetic analysis and interventions become important for obtaining crop varieties with commercially valuable characteristics.

In the livestock industry, genetics can help increase the production of certain animals used in the food industry (cows, salmon, chickens). Also, with animals linked to sports (horses, bulls, dogs).

In evolutionary biology, genetic studies provide information at the population level.

In law, many contributions from genetics serve to determine the guilty parties in crimes and to clear up doubts regarding kinship relationships.

History of Genetics

German Rudolf Virchow introduced the principle of the continuity of life through cell division and established the cell as the unit of reproduction.

British Charles Darwin presented his theory of evolution in his book On the Origin of Species. He postulated that current organisms descend from beings that existed in the past and that underwent a process of inheritance with modifications.

The Czech Gregor Mendel, now considered the founder of genetics, established Mendel's laws, which were the first basic rules for the transmission of patterns through inheritance from parents to their offspring. At the time, his work was ignored.

Mendel's first law explains the uniformity of hybrids from the first filial generation. Mendel's second law explains segregation. Mendel's third law explains the independent transmission or independence of traits.

During the period known as "classical genetics," genetics emerged as a separate science with the rediscovery of Mendel's laws.

The Dane Wilhem Johannsen introduced the term "gene" to refer to the hereditary factors of Mendel's research.

Thomas Hunt Morgan and his group at Columbia University discovered the basis of the chromosomes found in every cell.

Alfred Sturtevant sketched the first genetic map showing the location of genes, among other important features.

It was confirmed that hereditary factors (or genes) are the basic unit of both functional and structural inheritance and are located on the chromosomes.

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.

During this period, the first DNA manipulation techniques emerged, and the first artificially conceived mice and flies were obtained through genetic engineering.

Lep-Chee Tsui, Francis Collins, and John Riordan discovered the defective gene that, when mutated, is responsible for the hereditary disease cystic fibrosis. The Human Genome Project was launched.

Ian Wilmut and Keith Campbell obtained the first cloned mammal (Dolly the sheep).

The Human Genome Project was successfully completed. This result ushered in a new era of genetic research, and the 21st century was dubbed “the century of genetics.”

Activity. Answer the following questions.

Remember to review the answers to the open-ended questions at the bottom of this page.

1. What is an allele?

2. What is the term used for autosomal inheritance that occurs when one allele dominates over another?

3. How is genetics used in the livestock industry?

4. How many chromosomes do humans normally have?

5. In what year was the first genetic map made?

Once you click this button, the questions will close and you will not be able to change your answer.

6. Why does a mutation occur?

7. What is the goal of genetic manipulation?

8. What is genetic variability?

9. What is the most important aspect of genetics?

10. A person with a variant gene is called...

Still have questions?

We recommend visiting the following material for greater knowledge or understanding of the topic:

Answers to open-ended questions:

8. It is a set of variants that exist for the same gene within individuals of the same population.

2. Salcedo, M. (2024, 25 diciembre). Genética - Qué es, tipos, importancia e historia. Concepto. https://concepto.de/genetica-2/

3. Equipo editorial, Etecé. (2024a, diciembre 25). Manipulación Genética - Concepto, ética, legalidad y ejemplos. Concepto. https://concepto.de/manipulacion-genetica/