What is a Chromosome?

Overview of DNA and Genes

• DNA is a spiraling chain-like molecule composed of 4 nucleotides: A, C, T, G.
• A gene is a stretch of DNA with a specific sequence of nucleotides that codes for something, usually a protein.
• Proteins interact to form living cells, tissues, organs, and ultimately entire organisms.

Genetic Variation

• Individuals exhibit different traits (e.g., beak shape) due to variations in their genetic code (mutations).
• Mutations can affect:
  • Protein shape and function
  • The timing or amount of protein production

What is a Chromosome?

• Definition: A chromosome is a complete chain of DNA paired with stabilizing proteins.
• Structure:
  • Not simply a container for DNA but a complex structure like a spool of yarn.
  • Composed of histones (protein orbs) wrapped with a string-like structure of DNA.
  • The DNA chain is extremely long (millions of nucleotides) and contains many genes.

Chromosome Form

• Chromosomes are tightly packaged during cell reproduction for durability.
• In most of the cell's life, chromosomes exist in a loose, noodle-like structure within the nucleus.

Human Chromosomes

• Humans have 23 pairs of chromosomes (total of 46).
• Each cell typically contains a full set of chromosomes.
• Different cell types (e.g., eye, liver) express different genes; non-relevant genes are turned off.

Chromosomal Inheritance

• Each chromosome pair consists of one chromosome from the mother and one from the father.
• Most pairs contain the same genes in the same locations, but slight sequence variations (mutations) exist.

Unique Mutations

• Unique mutations can occur in the sperm or egg, or early in development, leading to new genetic information.

Summary

• A chromosome consists of DNA and stabilizing proteins.
• Humans typically have 23 pairs of chromosomes in each cell.
• Chromosomes are loose during most of a cell's life and condensed during reproduction.

Presented by Jon Perry.
This animation was supported by viewers on Patreon.