Genetics and Biotechnology: A Deep Dive into Heredity and DNA
Heredity and Genes
Sons inherit parental characters. The world comprises two types of objects, both made of atoms and molecules. Living beings can create copies of themselves, unlike inert matter. Children inherit characteristics from their parents because living beings store and transmit information about themselves and how to reproduce.
Living beings evolve. Copies are nearly identical, yet slight variations are key to diversity and the evolution of species. Natural selection favors the fittest, similar to how breeders select the best through artificial selection.
Mendel: The difference lies in the genes. Darwin’s ideas about inherited traits blending were initially met with skepticism. Mendel demonstrated that heredity units (genes) do not mix. His experiments with pea plants, crossing tall green peas with short yellow peas, revealed that traits are transmitted independently. The first generation were all tall and yellow, but subsequent generations showed variations, proving that traits could reappear after skipping a generation.
Mendel’s conclusion: Heredity. Mendel’s work confirmed that hereditary factors remain distinct across generations. Two gene versions exist (one from each parent), with one sometimes dominant over the other. This hereditary factor was later termed “gene” by Johannsen in 1909. A gene is a unit of hereditary information controlling a specific trait.
Phenotype: The observable trait (e.g., blonde hair, blue eyes).
Genotype: The underlying genetic makeup.
Where are the genes? Genes reside in the cell nucleus within DNA, which directs protein synthesis and heredity.
Chromatin and chromosomes. Chromatin, a colored substance in cell nuclei, condenses into chromosomes during cell division (mitosis). Humans have 23 chromosome pairs, with one pair determining sex (XX for females, XY for males). Genes are segments of chromosomes.
Fertilization and genetic endowment. Sutton observed that grasshopper sex cells (gametes) have half the number of chromosomes as other cells. Human sex cells have 23 chromosomes, while other cells have 23 pairs.
What are genes made of?
Genes, composed of DNA, are the key to heredity. Watson and Crick’s 1953 discovery of the DNA double helix structure revolutionized genetics. X-ray diffraction of DNA fibers revealed a helical structure, and chemical analysis showed consistent base pairing.
DNA duplication. Genes are copied through DNA replication, where the double helix “unzips” and each strand serves as a template for a new complementary strand.
The purpose of genes? Genes transmit hereditary information and express it through the genetic code. This code uses groups of three nucleotides to specify amino acids, the building blocks of proteins.
- Nucleotides: Chemical compounds forming DNA strands, each with three components: nitrogenous bases, sugar, and phosphoric acid.
- Amino acids: Building blocks of proteins, which perform most biological functions.
From DNA to Proteins
Central dogma of molecular biology. Protein synthesis occurs on ribosomes in the cytoplasm. Since DNA resides in the nucleus, an intermediary molecule (RNA) carries genetic information to ribosomes.
Types of RNA:
- Ribosomal RNA (rRNA): Part of the ribosome structure.
- Transfer RNA (tRNA): Adapters linking mRNA codons to amino acids.
- Messenger RNA (mRNA): Carries the genetic message from DNA to ribosomes.
Protein synthesis: DNA in the nucleus transcribes its message to mRNA. mRNA exits the nucleus and binds to a ribosome in the cytoplasm. tRNA molecules bring specific amino acids to the ribosome based on the mRNA sequence, assembling the protein.
The Human Genome and Beyond
DNA sequencing. Not all DNA encodes. The Human Genome Project completed the human DNA sequence in 2003. Humans have about 23,000 genes, representing only 2% of the genome. Much of the DNA consists of non-coding sequences called introns.
- Exons: DNA segments within a gene that code for proteins.
- Introns: Non-coding DNA segments within a gene.
Genome and complexity. Genomics studies genomes and their role in diseases like cancer. Some genes encode multiple proteins, increasing the number of proteins beyond the number of genes. Proteomics studies all proteins encoded by the genome.
Manipulating Genes
Recombinant DNA technology allows scientists to manipulate DNA. Cloning creates copies of DNA fragments.
Biotechnology tools:
- Restriction enzymes: Cut DNA at specific sites.
- DNA ligase: Joins DNA fragments.
- Plasmids: Small DNA molecules used as vectors to carry genes into bacteria.
Biotechnology: In 1972, Boyer and Cohen cloned the first gene, inserting human genetic information into bacteria to produce human proteins. This led to the biotechnology industry, producing human insulin, interferon, growth hormone, and vaccines.
Polymerase chain reaction (PCR). PCR, invented by Mullis in 1986, amplifies DNA samples quickly.
Transgenic organisms. Genetically modified organisms carrying foreign genes have been created, including bacteria that degrade pollutants and plants resistant to insects.
Stem Cells and Cloning
Stem cells are undifferentiated cells that can develop into various cell types. They hold promise for generating tissues and organs. Types of stem cells include embryonic stem cells, umbilical cord stem cells, and induced pluripotent stem cells (iPSCs).
Gene Therapy
Gene therapy aims to cure hereditary diseases by modifying genes.