Difference Between Normal and Abnormal Karyotype

Key Difference – Normal vs Abnormal Karyotype
 

Chromosomes contain the genetic information of an organism, but the chromosomal numbers vary among different species. A healthy human has 46 chromosomes arranged in 23 pairs. There are 22 pairs of autosomes and one pair of sex chromosomes. There are thousands to millions of genes located in the chromosomes which bear the genetic codes to synthesize essential proteins necessary for growth, development, and reproduction. The number and physical structures of chromosomes reveal important information regarding the organism. Hence, scientists study the total chromosomes of the organisms. Karyotype is a diagram which shows the chromosomal number and constitution in the cell nucleus. It reveals information regarding the number, size, shape, centromere position of the chromosomes, etc. under the light microscope. If a karyotype shows a usual number and structure of chromosome set, it is known as a normal karyotype. Abnormal karyotype shows an unusual number or structurally malformed chromosomes in the karyotype. This is the key difference between normal and abnormal karyotype.

CONTENTS
1. Overview and Key Difference
2. What is a Normal Karyotype
3. What is an Abnormal Karyotype
4. Side by Side Comparison – Normal vs Abnormal Karyotype
5. Summary

What is a Normal Karyotype?

Normal karyotype is a diagram which shows the correct number and structure of the complete set of the chromosomes in a cell or of an individual. Human has 23 pairs of chromosomes in which 22 pairs are autosomes and one is sex chromosomes. Each chromosome has a specific size, shape and centromere position. Karyotype of a healthy human can be considered as a normal karyotype. In a normal karyotype, there are no missing sequences or changes in genetic information.

Human chromosomes can be grouped into seven groups based on the length and morphology. 42 chromosomes are autosomes coded for different traits.  The sex chromosome pair (X and Y) decides the gender of the individual and sex-related traits. By analyzing the karyotype of the organism, it is possible to detect the genetic disorders and many other information about the individual. A karyotype can reveal several important information. It tells the gender of the individual and reveals the species to which the individual belongs. Finally, a karyotype can indicate whether the individual has a chromosomal disorder which leads to a genetic disease.

Karyotyping is a technique performed by the doctors to examine complete set of the chromosomes in the nucleus. Chromosomes are visible only during the metaphase of the cell division. Total chromosomes are collected and analyzed during the test to determine whether there are numerical or structural abnormalities in chromosomes of the organism.

Figure 01: Normal karyotype of a human

What is an Abnormal Karyotype?

Organisms have a specific number and structure of chromosomes. However, due to different reasons, organisms can bear an unusual number of chromosomes and structurally malformed chromosomes. These changes can cause serious genetic disorders. Hence, karyotyping is an important procedure to reveal such genetic conditions in organisms.

Chromosomal abnormalities are main two types named numerical aberrations and structural aberrations. When chromosomes are observed under the microscope, it is possible to identify abnormalities such as extra chromosomes, missing chromosomes, missing parts of the chromosomes, extra portions of the chromosomes, portions broken from one chromosome and attached to another chromosome, etc. If a karyotype has an unusual number of chromosomes or structurally changed chromosomes, it is known as an abnormal karyotype as shown in figure 02.

There are different disease syndromes due to abnormal karyotypes in human such as down syndrome, Klinefelter syndrome, turner syndrome, sickle cell disease, cystic fibrosis, etc. Down syndrome is caused due to the trisomy of the chromosome 21. Klinefelter syndrome is another syndrome which is caused due to extra X chromosome in males.

Figure 02: An abnormal human karyotype (Human chromosome XXY)

What is the difference between Normal and Abnormal Karyotype?

Summary – Normal vs Abnormal Karyotype

A normal karyotype of a human contains a total of 46 chromosomes with correct sizes and shapes. There are 22 autosomal chromosome pairs and one sex chromosome pair in a normal human karyotype. When there are genetic disorders, they are reflected by the chromosomal abnormalities. Chromosomal abnormalities can be either numerical or structural. Both will result in abnormal karyotypes. Abnormal karyotype contains an unusual number of chromosomes or chromosomes with structural changes. This is the difference between a normal karyotype and an abnormal karyotype.

Reference:
1. Yang, S., G. Lin, Y. Q. Tan, L. Y. Deng, D. Yuan, and G. X. Lu. “Differences between karyotypically normal and abnormal human embryonic stem cells.” Cell proliferation. U.S. National Library of Medicine, June 2010. Web. 03 May 2017
2. Connor, Clare O. “Karyotyping for Chromosomal Abnormalities.” Nature News. Nature Publishing Group, 2008. Web. 03 May 2017

Image Courtesy:
1.” Karyotype (normal)”By National Cancer Institute – This image was released by the National Cancer Institute, an agency part of the National Institutes of Health (Public Domain) via Commons Wikimedia
2. “Human chromosomesXXY01” By User:Nami-ja – Own work (Public Domain) via Commons Wikimedia

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