Chromosomes

Chromosome: Strands of DNA compressed and organized into a double helix structure. Humans typically have 23 pairs of chromosomes.

Source: RDCRN (NCATS/NIH)1

   •   •   •

Chromosome: Microscopic particles within the cells of our bodies that contain genes.

Source: RDCRN (NCATS/NIH)2

Introduction: Chromosomes

Chromosome — A microscopic rod-shaped structure present in the nucleus of all body cells except red blood cells. Chromosomes store genetic information (genes). Normally, humans have 23 pairs for a total of 46 chromosomes. In each pair, one chromosome is inherited from the mother and one from the father.

Source: RDCRN (NCATS/NIH)3

Introduction: Chromosomes

Chromosome — composed of DNA molecules (genes) that help make up organisms

Source: RDCRN (NCATS/NIH)4

Introduction: Chromosomes

Chromosome—A compact structure containing DNA and proteins present in nearly all cells of the body. Chromosomes carry genes, which direct the cell to make proteins and direct a cell's construction, operation, and repair. Normally, each cell has 46 chromosomes in 23 pairs. Each biological parent contributes one of each pair of chromosomes.

Source: NIA (NIH)5

Introduction: Chromosomes

Chromosomes

Genes are packaged in bundles called chromosomes. In humans, each cell in the body contains 23 pairs of chromosomes - 46 in total.

You inherit one of each pair of chromosomes from your mother and one from your father. This means there are two copies of every gene in each cell, with the exception of the sex chromosomes, X and Y.

The X and Y chromosomes determine the biological sex of a baby. Babies with a Y chromosome (XY) will be male, and those without a Y chromosome will be female (XX).

This means that males only have one copy of each X chromosome gene, rather than two, and they have a few genes found only on the Y chromosome that play an important role in male development.

Occasionally, individuals inherit more than one sex chromosome. Females with three X chromosomes (XXX) and males with an extra Y (XYY) are normal, and most never know they have an extra chromosome.

However, females with one X have a condition known as Turner syndrome, and males with an extra X have Klinefelter syndrome.

The whole set of genes is known as the genome. Humans have about 21,000 genes on their 23 chromosomes, plus 37 genes in their mitochondria.

Mitochondria are small structures inside cells that allow the cell to get energy from sugar and fat, and they're only passed on within eggs. This means mitochondrial DNA is only inherited from mothers.

Source: NHS Choices UK6

Introduction: Chromosomes

What is a chromosome?

In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.

Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.

Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.

Source: GHR (NLM/NIH)7

Introduction: Chromosomes

Our genetic information is stored in 23 pairs of chromosomes that vary widely in size and shape. Chromosome 1 is the largest and is over three times bigger than chromosome 22. The 23rd pair of chromosomes are two special chromosomes, X and Y, that determine our sex. Females have a pair of X chromosomes (46, XX), whereas males have one X and one Y chromosomes (46, XY). Chromosomes are made of DNA, and genes are special units of chromosomal DNA. Each chromosome is a very long molecule, so it needs to be wrapped tightly around proteins for efficient packaging.

Near the center of each chromosome is its centromere, a narrow region that divides the chromosome into a long arm (q) and a short arm (p). We can further divide the chromosomes using special stains that produce stripes known as a banding pattern. Each chromosome has a distinct banding pattern, and each band is numbered to help identify a particular region of a chromosome. This method of mapping a gene to a particular band of the chromosome is called cytogenetic mapping. For example, the hemoglobin beta gene (HBB) is found on chromosome 11p15.4. This means that the HBB gene lies on the short arm (p) of chromosome 11 and is found at the band labeled 15.4.

Source: NCBI, Genes and Disease (NCBI/NIH)8

   •   •   •

Chromosomes: In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)9

Anatomical Information about Chromosomes

What are chromosomes?

Chromosomes are organized packages of DNA found inside your body's cells.[1] Your DNA contains genes that tell your body how to develop and function. Humans have 23 pairs of chromosomes (46 in total). You inherit one of each chromosome pair from your mother and the other from your father. Chromosomes vary in size. Each chromosome has a centromere, which divides the chromosome into two uneven sections. The shorter section is called the p arm, and the longer section is called the q arm.[1, 2] Genetics Home Reference (GHR) has a helpful picture of a chromosome.

Source: GARD (NIH)10

   •   •   •

Are there different types of chromosomes?

Yes, there are two different types of chromosomes; sex chromosomes and autosomal chromosomes. The sex chromosomes are the X and Y chromosomes. They determine your gender (male or female). Females have two X chromosomes, XX, one X from their father and one X from their mother. Males have one X chromosome from their mother and one Y chromosome, from their father, XY. Mothers always contribute and X chromosome (to either their son or daughter). Fathers can contribute either an X or a Y, which determines the gender of the child. The remaining chromosomes (pairs 1 through 22) are called autosomal chromosomes. They contain the rest of your genetic information.[1, 2][3, 4]

Source: GARD (NIH)11

Types

Types may include:12

Types of Chromosome:

  • Autosome
  • Human Chromosome
  • Interphase Chromosome
  • Mitotic Chromosome
  • Pre-Condensed Chromosomes
  • Sex Chromosome

Anatomy Articles

Read about these related anatomy topics:

Disease and Condition Articles

Read about these related conditions and diseases:

Related Disease and Condition Topics

Read about these diseases and medical conditions related to Chromosomes:

... More »

   •   •   •

References

  1. Source: RDCRN (NCATS/NIH): rarediseasesnetwork.org/ cms/ artfl/ Learn-More/ Glossary
  2. Source: RDCRN (NCATS/NIH): rarediseasesnetwork.org/ cms/ bvmc/ Learn-More/ Glossary
  3. Source: RDCRN (NCATS/NIH): rarediseasesnetwork.org/ cms/ bbd/ Learn-More/ Glossary
  4. Source: RDCRN (NCATS/NIH): rarediseasesnetwork.org/ cms/ dsc/ Learn-More/ Glossary
  5. Source: NIA (NIH): nia.nih.gov/ health/ alzheimers-disease-genetics-fact-sheet
  6. Source: NHS Choices UK: nhs.uk/ conditions/ Genetics/ 
  7. Source: GHR (NLM/NIH): ghr.nlm.nih.gov/ primer/ basics/ chromosome
  8. Source: NCBI, Genes and Disease (NCBI/NIH): ncbi.nlm.nih.gov/ books/ NBK22266/ 
  9. Source: MeSH (U.S. National Library of Medicine)
  10. Source: GARD (NIH): rarediseases.info.nih.gov/ guides/ pages/ 73/ faqs-about-chromosome-disorders
  11. ibid.
  12. Source: NCI Thesaurus

   •   •   •

Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.