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Chromosome pairs

Review your understanding of chromosome pairs in this free article aligned to NGSS standards.

Key points:

  • Every species has its own specific number of chromosomes. For example, humans have 46 chromosomes in a typical body cell.
  • Many species have chromosomes that come in matched pairs. For example, the 46 chromosomes in a human cell can be organized into 23 pairs.
  • These paired chromosomes are called homologous chromosomes. Homologous chromosomes are the same size and shape.
  • Homologous chromosomes contain the same genes. However, they may have different alleles, or versions, of those genes.
  • Scientists and medical professionals can use a karyotype to view an organism’s sets of chromosomes. In a karyotype, pairs of homologous chromosomes are arranged next to each other. This makes it easier to see if there are any differences between chromosomes that may lead to a genetic condition.
A picture shows 46 chromosomes lined up in two rows. The chromosomes are arranged in pairs.
A human karyotype. Image credit: “Karyotype from a female human lymphocyte (46, XX)" by Andreas Bolzer, Gregor Kreth, Irina Solovei, Daniela Koehler, Kaan Saracoglu, Christine Fauth, Stefan Müller, Roland Eils, Christoph Cremer, Michael R. Speicher, Thomas Cremer, CC BY 2.5.

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