DNA: Duplicated and Homologues
Difference between Homologous and Replicated Chromosomes
Sexual reproducers have 2 sets of homologous chromosomes. Cells must duplicate DNA prior to cell division. What is the distinction between duplicates and homologues?
Students often become confused during discussions of genetics when it comes to the terminology associated with chromosomes and chromosome number. What are homologous chromosomes? What are duplicated chromosomes? What are chromatids? How do all of these terms differ and how do they relate to each other? The intent of this article series is to clarify the lingo of chromosomes.
Homologous Chromosomes
Most of the cells in our bodies are somatic, or the non sex cells of our body, and have a diplod (2n) chromosome number, meaning that chromosomes come in pairs called homologues.
Every somatic cell in your body has 46 chromosomes. You received a set of 23 from your mother’s egg and a matching (homologous) set of 23 via your father’s sperm, and now these chromosomes are the genetic material inside nearly every cell of your body, every cell containing 23 pairs of homologous chromosomes.
Duplicated DNA
Cells Divide to Make More Cells
During the cell cycle, somatic cells grow and divide. In this process, called mitosis, a single cell (‘parent cell’) splits into two identical ‘daughter cells’.
Copying DNA
Before a cell divides, it must make a copy of its DNA (nucleic acid) so that each daughter cell has a complete copy of genetic information. Each individual DNA molecule is the material of one chromosome, and the process of duplicating or copying the DNA is called replication.
Chromatin Condensing
Most of the time, the DNA molecules in each of your cells do not look like chromosomes, but instead are in very long strands called chromatin. When the DNA is undergoes the process of replication, it is in these long chromatin strands. But when the cell prepares to divide, it must “pack” its DNA for the move. So prior to cell division, the chromatin condenses.
Homologous, Duplicated Chromosomes
This replicated DNA molecule, in its condensed form, is now referred to as a chromosome. But, remember, there are two copies attached to each other until the genetic material is split so that each new cell gets a copy. At this point, we have 23 pairs of homologous, duplicated chromosomes.
More Information
See the science education website Science Prof Online to learn more about cell biology or look to additional Suite101 biology articles, including Chromosomes & Sister Chromatids, Sexual and Asexual Reproduction, and Mitosis & Meiosis Comparison.
Sources
Campbell, N. A. & Reece J. B. (2005) Biology, seventh edition. Pearson Education Inc.
Campbell, N. A., Reece J. B. & Simon, E. (2004) Essential Biology with Physiology. Pearson Education Inc.
