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Basics of Chromosomes

Basics of Chromosomes

A chromosome is an organized package of DNA found in the nucleus of the cell. Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes--22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.

Basics of Chromosomes
Images and animations are courtesy of the National Human Genome Research Institute's Talking Glossary (

Materials for Basics of Chromosomes


Chromosome Map 3D Animation

Description: View a 3D animation of a chromosome map.

DNA Molecule - How DNA is Packaged

Description: Watch this 1 minute animation of the packaging of DNA into chromosomes.



Description: This article addresses common questions, such as What is a Chromosome? Do all living things have the same types of chromosomes? and What are telomeres?

Chromosomes and Cytogenetics

Description: Detailed information on chromosome structure, analysis, and disorders

What Is a Chromosome Disorder?

Description: A chromosome disorder results from a change in the number or structure of chromosomes.

What is a Chromosome?

Description: Chromosomes are bundles of tightly coiled DNA, located, in pairs, within the nucleus of almost every cell in our body. Humans have 23 pairs of chromosomes.

What is a Telomere?

Description: Telomeres are distinctive structures found at the ends of our chromosomes. They consist of the same short DNA sequence repeated over and over again.


Make a Karyotype

Description: Practice identifying chromosomes in a karyotype by playing this interactive matching game.

Interactive Tutorials

Chromosomes Carry Genes

Description: An interactive Web site exploring basic concepts of DNA packaging through historical discovery

Genes Get Shuffled When Chromosomes Exchange Pieces

Description: An interactive Web site exploring basic concepts of genetic recombination through historic discovery

Specialized Chromosomes Determine Gender

Description: An interactive Web site exploring basic concepts of inheritance through historical discovery

Labs & Experiments

Recombination Calculations by Branch Diagrams

Description: An expert authored advanced classroom laboratory experiment teaching a method for analyzing genetic recombination events

Teacher Resources

Analyzing Chromosomes (PDF 7,056.8 KB, Lesson Plans/Lesson Activities)

Description: Students learn about chromosome analysis by completing a partial karyotype and assess the karyotype for anomalies. Students practice sharing bad news to parents.

X or Y: Does it Make a Difference? (Lesson Plans/Lesson Activities)

Description: Students learn and describe the functional differences between X and Y chromosomes, and explain the significance of these differences in the human genome.


Molecular Basis of Heredity: Part 2. Genomes

Description: Raye Lynn Alford, PhD, explains the structures and functions of genomes, and discusses how chromosomal changes lead to certain genetic disorders.