What is a Chromosome?

Introduction

• DNA is a spiraling, chain-like molecule made up of 4 nucleotides: A, C, T, G.
• A gene is a specific sequence of nucleotides that codes for proteins.

Genes and Proteins

• Genes typically code for proteins or groups of proteins.
• In multi-celled organisms, proteins interact to form living cells which make up tissues, organs, and ultimately entire organisms.
• Differences in traits (e.g., beak shape) arise from mutations in genetic code.
  • Mutations can change protein shape/function or regulate protein production.

Understanding Chromosomes

• A chromosome consists of a long chain of DNA and stabilizing proteins.
• Common misconception: DNA is not trapped inside the chromosome but rather organized in a specific structure.

Structure of Chromosomes

• DNA is wrapped around histone proteins, forming a fiber.
• This fiber appears as a condensed yarn-like form during cell reproduction for durability.
• Most of the time, chromosomes exist in a loose, noodle-like structure inside the cell nucleus.

Human Chromosomes

• Humans have 23 pairs of chromosomes (46 total).
• Each cell typically contains a full set of chromosomes, with unique genes activated based on cell type.
  • Example: Eye cells only use eye-specific genes, while liver cells use liver-specific genes.
• Each pair of chromosomes consists of one from the mother and one from the father.

Genetic Variations

• Chromosomes of each pair generally contain the same genes in the same locations.
• Mutations can cause slight variations in the genetic sequence.
  • Some mutations are inherited; others are unique to the individual, resulting from changes early in development.
• Unique mutations add new genetic information that may not have existed before.

Summary

• Definition of a Chromosome: A chromosome is a DNA chain with stabilizing proteins.
• Human Chromosome Count: 23 pairs (46 total) in each cell.
• Chromosomes exist in a loose structure during most of the cell's life and condense for reproduction.