Riassunto analitico
Elements of general human genetics
A trait, as related to genetics, is a specific characteristic of an individual. Traits can be determined by genes, environmental factors or by a combination of both. Traits can be qualitative (such as eye colour) or quantitative (such as height or blood pressure). A given trait is part of an individual’s overall phenotype.
As previously mentioned, traits (and, therefore, one induvidual’s own phenotype) can be influenced by the environment, genes, or a combination of both.
While it could be quite straightforward to determine what one means when talking about “environment”, the exact definition of the word “gene” has long been a source of scientific debate. A simple way to think about it is as follows: proteins are the brick and mortar that make up our cells and tissues. And genes are the part of our genome that encodes the information for making those proteins. For example, the human genome has roughly 20,000 protein-coding genes.
Interestingly, all the information for those 20,000 protein-coding genes is encoded by only 1.5% of the entire human genome. A more expansive definition of a gene includes those segments of DNA that encode information for making an RNA molecule that functions in some fashion other than directly coding for a protein; these are sometimes referred to as RNA genes.
As genes, being part of the genome, are passed down by parents to their offspring during reproduction, the mechanisms of inheritance (i.e. the way in which the genetic information in passed from a parent to a child) are of the outmost importance when it comes to the study of human genetics.
Mendelian inheritance, for example, refers to certain patterns of how traits are passed from parents to offspring. These general patterns were established by the Austrian monk Gregor Mendel, who performed thousands of experiments with pea plants in the 19th century. Mendel’s discoveries of how traits (such as color and shape) are passed down from one generation to the next introduced the concept of dominant and recessive modes of inheritance. The main patterns of inheritance include: Autosomal Dominant, Autosomal Recessive, X-linked Dominant, X-linked Recessive and Mitochondrial. 1
When dealing with human genetic, especially in the context of Mendelian inheritance, it is of the utmost importance to corrtectly define two terms which are often (wrongly) used interchangebabely: polymorphism and mutation.
The term polymorphism refers to the presence of two or more variant forms of a specific DNA sequence that can occur among different individuals or populations. Mutations, on the other hand, can be defined as changes in the DNA sequence resulting from errors in DNA replication during cell division, their significance stems from their ability to sometimes lead to development of diseases. When such mutations are passed from parents to their offspring through mendelian inheritance mechanisms, they may lead to the development of so called “mendelian diseases”.
To date, 6,468 single gene disorders and traits phenotype, caused by 4,545 Genes have been observed and classified by the OMIM (Online Mendelian Inheritance in Man) Compendium (https://www.omim.org/about).
Quantitative (or Continuous) traits
Any variable quantitative character that depends on the additive action of a large number of small independent causes (whether genetic or not) will show a Normal (Gaussian) distribution in the population. These distributions are described using two parameters: the mean and the standard deviation. Some examples of quantitative traits which distribute following such a pattern, areheight, weight and arterial blood pressure.
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Abstract
Elements of general human genetics
A trait, as related to genetics, is a specific characteristic of an individual. Traits can be determined by genes, environmental factors or by a combination of both. Traits can be qualitative (such as eye colour) or quantitative (such as height or blood pressure). A given trait is part of an individual’s overall phenotype.
As previously mentioned, traits (and, therefore, one induvidual’s own phenotype) can be influenced by the environment, genes, or a combination of both.
While it could be quite straightforward to determine what one means when talking about “environment”, the exact definition of the word “gene” has long been a source of scientific debate. A simple way to think about it is as follows: proteins are the brick and mortar that make up our cells and tissues. And genes are the part of our genome that encodes the information for making those proteins. For example, the human genome has roughly 20,000 protein-coding genes.
Interestingly, all the information for those 20,000 protein-coding genes is encoded by only 1.5% of the entire human genome. A more expansive definition of a gene includes those segments of DNA that encode information for making an RNA molecule that functions in some fashion other than directly coding for a protein; these are sometimes referred to as RNA genes.
As genes, being part of the genome, are passed down by parents to their offspring during reproduction, the mechanisms of inheritance (i.e. the way in which the genetic information in passed from a parent to a child) are of the outmost importance when it comes to the study of human genetics.
Mendelian inheritance, for example, refers to certain patterns of how traits are passed from parents to offspring. These general patterns were established by the Austrian monk Gregor Mendel, who performed thousands of experiments with pea plants in the 19th century. Mendel’s discoveries of how traits (such as color and shape) are passed down from one generation to the next introduced the concept of dominant and recessive modes of inheritance. The main patterns of inheritance include: Autosomal Dominant, Autosomal Recessive, X-linked Dominant, X-linked Recessive and Mitochondrial. 1
When dealing with human genetic, especially in the context of Mendelian inheritance, it is of the utmost importance to corrtectly define two terms which are often (wrongly) used interchangebabely: polymorphism and mutation.
The term polymorphism refers to the presence of two or more variant forms of a specific DNA sequence that can occur among different individuals or populations. Mutations, on the other hand, can be defined as changes in the DNA sequence resulting from errors in DNA replication during cell division, their significance stems from their ability to sometimes lead to development of diseases. When such mutations are passed from parents to their offspring through mendelian inheritance mechanisms, they may lead to the development of so called “mendelian diseases”.
To date, 6,468 single gene disorders and traits phenotype, caused by 4,545 Genes have been observed and classified by the OMIM (Online Mendelian Inheritance in Man) Compendium (https://www.omim.org/about).
Quantitative (or Continuous) traits
Any variable quantitative character that depends on the additive action of a large number of small independent causes (whether genetic or not) will show a Normal (Gaussian) distribution in the population. These distributions are described using two parameters: the mean and the standard deviation. Some examples of quantitative traits which distribute following such a pattern, areheight, weight and arterial blood pressure.
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