Understanding Genetics

Explore the fundamental principles of heredity, DNA, and the building blocks of life

DNA Structure

The blueprint of life encoded in a elegant double helix

The Double Helix

DNA (deoxyribonucleic acid) is composed of two polynucleotide chains that coil around each other to form a double helix. This structure was discovered by James Watson and Francis Crick in 1953.

  • Sugar-phosphate backbone: Forms the outer structure
  • Nitrogenous bases: A, T, G, C pair in the center
  • Base pairing rules: A pairs with T, G pairs with C
  • Antiparallel strands: Run in opposite directions
A-T G-C T-A C-G A-T

DNA Replication

How cells make perfect copies of their genetic material

Original DNA Parent New Parent New Fork moves

Semi-Conservative Replication

DNA replication ensures each new cell receives an identical copy of genetic information. The process is called "semi-conservative" because each new DNA molecule contains one original strand and one newly synthesized strand.

  • Helicase: Unwinds the double helix
  • Primase: Lays down RNA primers
  • DNA Polymerase: Adds new nucleotides
  • Ligase: Joins Okazaki fragments

Mendelian Inheritance

The patterns of how traits are passed from parents to offspring

Gregor Mendel's Laws

In the 1860s, Gregor Mendel discovered the basic principles of heredity through his experiments with pea plants. His work laid the foundation for modern genetics.

  • Law of Segregation: Alleles separate during gamete formation
  • Law of Independent Assortment: Genes for different traits are inherited independently
  • Dominant vs Recessive: Some alleles mask others
  • Genotype vs Phenotype: Genetic code vs. physical expression
R r R r RR Rr Rr rr Round Wrinkled Parent 1 Parent 2

Autosomal Dominant

Only one copy of the mutated gene is needed to express the trait. Affected individuals have at least one affected parent.

Autosomal Recessive

Two copies of the mutated gene are required. Carriers have one copy but don't show symptoms.

X-Linked

Genes located on the X chromosome. Males are more frequently affected since they have only one X chromosome.

Gene Expression

From DNA code to functional proteins: the central dogma of biology

DNA Transcription mRNA Translation Protein In Nucleus: RNA polymerase reads DNA template and synthesizes complementary mRNA In Cytoplasm: Ribosomes read mRNA codons and assemble amino acids into proteins

The Central Dogma

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein. This follows the central dogma of molecular biology: DNA → RNA → Protein.

  • Transcription: DNA is copied into mRNA in the nucleus
  • RNA Processing: Introns are removed, exons joined
  • Translation: mRNA is decoded at ribosomes
  • Protein Folding: Amino acid chains fold into 3D structures

Genetic Mutations

Changes in DNA sequence that can alter protein function

Types of Mutations

Mutations are changes in the DNA sequence that can occur spontaneously or be induced by mutagens. They can have various effects on organism fitness.

  • Point Mutation: Single nucleotide change (substitution)
  • Insertion: Extra nucleotides added
  • Deletion: Nucleotides removed
  • Frameshift: Alters the reading frame
Original: A T G C A Substitution: A T C C A G→C Deletion: A T G A ✗ Insertion: A T G T C A

Silent Mutation

DNA change doesn't affect the amino acid sequence due to genetic code redundancy. No impact on protein function.

Missense Mutation

Results in a different amino acid. May or may not affect protein function depending on the change.

Nonsense Mutation

Creates a premature stop codon, truncating the protein. Often has severe functional consequences.