Fundamentals of Genetics

In this lesson, you are introduced to genetics, a fundamental branch of biology that holds great significance in both biology and medicine. Genetics is the study of genes, which are the basic units of heredity responsible for passing traits from parents to offspring. At the molecular level, genes are composed of DNA, a molecule structured as a double helix. DNA contains four key nucleotide bases: adenine, thymine, cytosine, and guanine, which pair specifically (A with T, and C with G) enabling precise DNA replication.

It is important to understand the difference between a gene and a chromosome; chromosomes are long DNA molecules carrying many genes. Humans typically possess around 20,000 to 25,000 genes, distributed across 23 pairs of chromosomes. These genes can exist in different versions called alleles, which contribute to genetic variation in populations. Central to molecular biology is the central dogma: DNA is transcribed into RNA, which is then translated into proteins, the functional molecules in the cell.

Transcription is the critical first step in gene expression, copying genetic information from DNA to messenger RNA (mRNA). Following this, translation synthesizes proteins based on the mRNA sequence. Changes or mutations in DNA can alter gene function and lead to different traits or phenotypes. In mendelian genetics, traits can be dominant or recessive, and organisms may have homozygous (two identical alleles) or heterozygous (two different alleles) genotypes, affecting trait inheritance.

Another source of genetic variation is genetic recombination during meiosis, which shuffles alleles to create unique genetic combinations. Additionally, environmental factors interact with genetics to influence traits, demonstrating that heredity is not the sole determinant of an organism’s characteristics. The lesson also highlights the role of genetics in heredity and evolution, showing how genetic information shapes populations over time.

Beyond the coding regions, non-coding DNA plays emerging roles in regulating gene activity. Related to this is the field of epigenetics, which studies modifications that affect gene expression without altering the DNA sequence itself. Finally, the practical applications of genetics span medicine, agriculture, and biotechnology, demonstrating genetics’ broad impact on science and society.