Solving a Genetic Mystery

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Chromosome: a long, thread-like molecule made of the chemical called DNA (deoxyribonucleic acid) that is held together with special proteins and is visible (with strong microscopes) during cell division... more

Gene: a region of DNA that instructs the cell on how to build protein(s). As a human, you usually get a set of instructions from your mom and another set from your dad... more

Karyotype: an image of chromosomes which shows their shape, size, and number.

Chromosomes and Genes

Take a moment to consider how traits are passed from parent to offspring inside the cell. The information for the traits of an organism is stored in DNA, as genes on chromosomes. All living things have genes and chromosomes. Depending on the plant or animal, the size and number of chromosomes are different. Think of chromosomes as giant set of instructions for living things.

Chromosomes Two-By-Two

Chromosomes come in matching pairs, one pair from each parent. Humans, for example, have a total of 46 chromosomes, 23 from the mother and another 23 from the father. With two sets of chromosomes, children inherit two copies of each gene, one from each parent.

The image below, call a karyotype, shows the chromosomes of a human, lined up in pairs. The only two chromosomes that do not always come in matching pairs are the sex chromosomes, X and Y. In humans, girls have two matching X chromosomes. Boys, however, have a Y chromosome and only one X chromosome. By looking at the sex chromosomes in the image below, we can tell that the person this karyotype belongs to is male.

Male Human Chromosomes


Additional images and illustrations from Wikimedia. Ant picture taken by en:User:Ways

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Bibliographic details:

  • Article: Chromosomes and Genes
  • Author(s): Sabine Deviche
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: July 20, 2010
  • Date accessed: February 23, 2024
  • Link:

APA Style

Sabine Deviche. (2010, July 20). Chromosomes and Genes. ASU - Ask A Biologist. Retrieved February 23, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Sabine Deviche. "Chromosomes and Genes". ASU - Ask A Biologist. 20 July, 2010.

MLA 2017 Style

Sabine Deviche. "Chromosomes and Genes". ASU - Ask A Biologist. 20 Jul 2010. ASU - Ask A Biologist, Web. 23 Feb 2024.

Modern Language Association, 7th Ed. For more info, see
Myrmecia ant
Different species have different numbers of chromosomes. This jack jumper ant has the least number of chromosomes among all animals: two in females, one in males.

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