A chromosome is a long, thread-like structure that contains genes, the basic units of inheritance. Genes are segments of DNA, the molecule that encodes the genetic information in living organisms. Chromosomes are found in the nucleus of every cell in an organism.
The word "chromosome" comes from the Greek words for "color body" because they were first seen under a microscope in 1883 by German biologist Wilhelm von Waldeyer-Hartz, and appeared to be colored bodies.
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How many chromosomes do humans have?
Most human cells contain two sets of chromosomes, one set inherited from each parent. In humans, each cell contains 23 pairs of chromosomes, bringing the total number of chromosomes in the human cell to 46. One set of 23 comes from the mother's egg, and the other set comes from the father's sperm. The father's sperm contains either an X chromosome or a Y chromosome, and this determines the sex of an individual.
The role of chromosomes in genealogy research
Chromosomes play a crucial role in genealogy as they contain the genetic material that is passed down from parents to their offspring. The study of genealogy involves tracing family history and relationships over time, and DNA analysis has become an increasingly important tool in this process. By analyzing patterns of DNA inheritance, individuals can learn more about their ancestry and connect with relatives they may not have known existed.
One of the most common types of genetic testing used in genealogy is autosomal DNA testing. This type of testing analyzes DNA from both parents and can provide information about genetic ancestry going back several generations. By examining patterns of shared DNA, individuals can learn more about their ethnic background and potentially connect with distant relatives who share common ancestors.
Another type of genetic testing used in genealogy is Y-DNA testing, which examines the Y chromosome passed down from father to son. This type of testing is particularly useful for tracing paternal lineage and can be used to identify genetic relatives with the same surname. Similarly, mitochondrial DNA testing analyzes the DNA passed down from a mother to her children and can be used to trace maternal lineage.
The structure of a chromosome
Each chromosome is made up of two long strands of DNA, which are coiled around each other to form a double helix. The DNA strands are held together by chemical bonds called hydrogen bonds. The sequence of the DNA base pairs (A, T, C, G) determines the order of the genetic information on the chromosome.
Chromosomes are not visible in cells during most of the cell cycle because the DNA is tightly coiled around proteins called histones. During mitosis (cell division), the chromosomes condense and become visible. The length of a chromosome is very long, about 1 meter (3 feet). If all the DNA in one human cell were stretched out, it would be about 2 meters (6.5 feet) long!
Autosomes vs. sex chromosomes
The 23 pairs of chromosomes in humans can be divided into two groups: the 22 pairs of autosomes and the one pair of sex chromosomes. The autosomes are the chromosomes that determine all the traits that are not related to sex. The sex chromosomes are the X chromosome and the Y chromosome, and they determine an individual's sex. Females have two X chromosomes, while males have one X chromosome and one Y chromosome.
See also
Explore more about chromosomes
- MyHeritage DNA
- How to Use Chromosome Browsers for Genealogy, article on the MyHeritage Knowledge Base
- Genealogy Glossary: Common DNA Terms Explained, article by Daniella Levy on the MyHeritage Knowledge Base
- DNA Basics series on the MyHeritage Blog
- Using Chromosome Browsers, Segment Data and Triangulation, webinar by Michelle Leonard on Legacy Family Tree Webinars