Ask A Biologist heading

Chromosomes and Genes

show/hide words to know

  • 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 where a specific set of instructions for one trait is kept. We get some of our genes from our mother and some from our father... more
  • Karyotype: an image of chromosomes which shows their shape, size, and number.

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.

Jack jumper 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.


Facebook logo  Twitter logo  Google Plus logo

Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.

Donate icon Donate