Genetics Fundamentals: Terminology – Analytical Methods – Approaches

I. Terminology:

1. Polymorphism:

• Definition: The existence of two or more different genotypes in a population with a frequency of at least 1%.

• Characteristics:

• Corrects genetic information but does not have clear clinical consequences.

• Can be used as genetic markers in research.

• Example: ABO blood groups, eye color, hair type…

Note: The distinction between polymorphism and mutation is based on the frequency of occurrence in the population and the clinical consequences.

2. Mutation:

• Definition: A permanent change in the DNA sequence.

• Characteristics:

• Corrects genetic information and leads to clear clinical consequences, which can cause diseases or affect the body’s function.

• Can be gene mutations or chromosomal mutations.

• Example: Gene mutations causing albinism, chromosomal mutations causing Down syndrome…

3. Number of Base Pairs (Bp) in the Human Genome:

• Number: Approximately 3 billion base pairs (3 x 10^9 Bp).

• Note: The human genome includes DNA in the cell nucleus and DNA in mitochondria.

4. Loci (Plural of Locus):

• Definition: The specific location of a gene on a chromosome.

• Example: The locus of the gene encoding eye color is located on chromosome number 15.

5. Haplotype:

• Definition: A set of alleles at closely linked loci on the same chromosome.

• Application: Used in linkage disequilibrium (LD) studies to determine the location of disease-causing genes on chromosomes.

• Example: Haplotype AB on chromosome number 1 includes allele A at locus 1 and allele B at locus 2.

6. Penetrance:

• Definition: The proportion of individuals with the disease genotype who express the disease phenotype.

• Formula: P = number of individuals with the disease gene who express the disease / total number of individuals with the disease gene.

• Example: Disease gene A has a penetrance of 80% meaning that 80% of people carrying the disease gene A will express the disease.

7. Incomplete Penetrance:

• Definition: When the penetrance of a disease gene is less than 100%.

• Example: A disease gene with a penetrance of 70% means that 30% of people carrying the disease gene will not express the disease.

8. Expressivity:

• Definition: The severity of the disease in individuals with the same disease genotype and who express the disease.

• Characteristics: Expressivity can vary in severity, age of detection, affected organs…

• Example: Two people with the same disease gene A but one person expresses mild disease, the other expresses severe disease.

9. Mary Lyon:

• Work: Discovered the X-chromosome inactivation mechanism in females (Lyonization).

• Mechanism: One of the two X chromosomes in females will be randomly inactivated in developing cells.

10. Cytosine Methylation:

• Role: One of the main mechanisms leading to X-chromosome inactivation.

• Mechanism: Methylation occurs at the Xist region on the X chromosome, causing it to be packed more tightly and unable to be transcribed.

II. Analytical Methods:

1. Cytogenetics:

• Tools: Studying chromosomes using karyotyping and FISH (Fluorescent In Situ Hybridization) techniques.

• Application: Analyze chromosomal abnormalities in number and structure, diagnose genetic diseases.

2. Molecular Genetics:

• Technologies:

• Genomics: Studying the entire genome.

• Proteomics: Studying all proteins in a cell.

• In vitro & In vivo: Studying genetics in the test tube and in living organisms.

• Bioinformatics: Using information technology to process and analyze genetic data.

• 3D protein modeling: Building 3D structural models of proteins.

• Application: Determine DNA sequences, detect mutations, diagnose genetic diseases, develop gene therapy…

III. Approaches:

• Holistic approach: Combines analytical methods and other scientific disciplines (biology, medicine, chemistry…) to study genetics comprehensively and efficiently.

• Multidisciplinary approach: Combines knowledge and skills from various disciplines such as genetics, medicine, biology, chemistry… to effectively study genetics.

Note:

• Genetic knowledge is constantly being updated and developed.

• The application of analytical methods and genetic technologies should be carried out responsibly and ethically.

Conclusion:

Understanding the terminology, analytical methods, and approaches in genetics is essential to grasp the fundamental concepts of genetics and apply them to research and practical applications.