DNA Khan Academy

Inheritance and Genetics

• Observation of offspring sharing traits with parents has been recognized for ages.

• Scientific study of inheritance began with Gregor Mendel in the 1800s.

• Mendel's understanding was limited; the molecular basis of inheritance was not discovered until the mid-20th century.

Discovery of DNA

• Watson and Crick established the double helix structure of DNA in 1953, building on earlier work by Rosalind Franklin and others.

• DNA was first identified in the mid-1800s as a molecule within cell nuclei.

• The molecular basis of inheritance required a molecule that could contain information, replicate, and express that information.

Structure of DNA

• Described as a twisted ladder:

  • Backbone: Made from deoxyribose (sugar) and phosphate (acidic).

  • Rungs: Comprised of paired bases where genetic information is stored.

Bases of DNA

• Four nucleotide bases:

  • Adenine (A) pairs with Thymine (T).

  • Cytosine (C) pairs with Guanine (G).

• The sequence of these bases encodes genetic information, contributing to traits.

The Human Genome

• The human genome contains approximately 6 billion base pairs.

• Organized over 46 chromosomes (23 pairs).

• Average of about 100 million base pairs per chromosome.

Density and Replication of DNA

• DNA is incredibly compact; the radius is about one nanometer.

• DNA replication involves splitting the double helix; each half serves as a template for creating the other half.

  • A always pairs with T, and G always pairs with C during replication.

Visual Representation

• Visual aids, such as animations, can help in understanding the DNA double helix and its structural components.