The key difference between DNA segments and centimorgans is that DNA segment is a piece of nucleotide sequence while centimorgan is a unit of measurement that describes the length of a DNA fragment.
Chromosomes are threadlike structures in which the genetic information is hidden. They are composed of DNA and histone proteins. The human genome has 23 pairs of chromosomes. DNA in chromosomes is analyzed in genetics in order to detect genes and their phenotypes. The nucleotide sequence, the order of nucleotides, length of a specific nucleotide sequence and changes of nucleotides are important information in gene analysis. Centimorgan is the unit that describes the length of a DNA segment.
CONTENTS
1. Overview and Key Difference
2. What are DNA Segments
3. What are Centimorgans
4. Similarities Between DNA Segments and Centimorgans
5. Side by Side Comparison – DNA Segments vs Centimorgans in Tabular Form
6. Summary
What are DNA Segments?
DNA segments are pieces of DNA on chromosomes. They are specific fragments or sections of DNA. The distance between DNA segments is measured by centimorgans. Shared DNA segments are the DNA sequences common between two organisms. Therefore, shared DNA segments or matching segments are important when determining closely related organisms. That particular DNA segment is inherited from a common ancestor. The longer the shared segment is, the higher the probability that it was inherited from a common ancestor.
Figure 01: DNA Segment
DNA segments are composed of deoxyribonucleotides. Deoxyribonucleotides are made from four bases (A, T, G and C), deoxyribose sugar and a phosphate group. DNA is double-stranded, having two complementary DNA strands bonded by H bonds. DNA segments are present in all 46 chromosomes in the human genome.
What are Centimorgans?
Centimorgan or cM is the unit that describes the length of a piece of DNA. Therefore, it measures the length of the nucleotide sequence. In other words, centimorgan is the measuring unit of DNA. More specifically, it describes the distance between two positions of a chromosome. In genetic analysis, using centimorgans can indicate how much DNA you share with your relatives. Moreover, the length of the specific DNA segments that you share can also be clearly explained. The more DNA segments you share, the more centimorgans you share with someone, and the more you are closely related to that person.
Centimorgans are different from the units such as centimeter, kilometer, etc. which measure physical distances. Centimorgans measure probability than physical distances. Therefore, centimorgans basically explain the DNA segments that you have in common (shared segments) with others and the likelihood of sharing genetic traits. Based on the shared centimorgans, DNA tests can indicate relatedness of your DNA with relatives.
What are the Similarities Between DNA Segments and Centimorgans?
- The length of a DNA segment is expressed in centimorgans.
- Both DNA segments and centimorgans tell you how much DNA you share with a genetic relative.
What is the Difference Between DNA Segments and Centimorgans?
DNA segments are sections of DNA on chromosomes. Centimorgan is a unit that measures the length of a DNA segment. So, this is the key difference between DNA segments and centimorgans. DNA segments are nucleotide sequences, while centimorgan is a measuring unit.
The following infographic summarizes the difference between DNA segments and centimorgans.
Summary – DNA Segments vs Centimorgans
DNA segment is a piece of DNA on a chromosome. Shared segments and ancestral segments show the relationships between organisms. Centimorgan is the measuring unit of DNA. It describes the distance between two positions in the chromosome (DNA fragment) or length of a specific segment of DNA. Thus, this summarizes the difference between DNA segments and centimorgans.
Reference:
1. Hansen, Annelie. “Centimorgan Chart: Understanding Your DNA Results”. Familysearch Blog, Available here.
2. “What Are Shared DNA Segments?” MyHeritage, Available here.
Image Courtesy:
1. “Dna segment” By Geneious Basic 4.0.2 (CC BY-SA 3.0) via Commons Wikimedia