Problems in the number of chromosomes (called chromosomal abnormalities) can be detected in an organism by studying karyotypes. The most common chromosomal abnormalities are caused when the chromosomes do not separate properly during meiosis (cell division). A monosomy is when only one homologous chromosome is present in the organism. If there is a nondisjunction at chromosome 23, the result could be monosomy 23 with XO also called Turner’s Syndrome.

 Image shows a Karyotype that only has one chromosome on the 23rd pair

Image Adapted From: Turners Syndrome, Biology Corner

 

Image shows a Karyotype that has three chromosomes on the 21st pair.

Image Adapted From: Trisomy 21, Biology Corner

Trisomy is when the organism has three copies of a homologous chromosome. The following are examples of three of the more common nondisjunction chromosomal abnormalities.
If there is a nondisjunction at chromosome 21, the result could be trisomy 21 (three #21 chromosomes) also called Down Syndrome.

 

If there is a nondisjunction at chromosome 23, the result could be trisomy 23 with XXY also called Klinefelter’s Syndrome.

 Image shows a Karyotype that has three chromosomes on the 23rd pair.

Image Adapted From: Klinefelter’s Syndrome, Biology Corner

 

Karyotype of a Normal Male

Image Adapted From: Normal Male Karyotype, Biology Corner

Compare the karyotype of a normal male to three abnormal karyotypes. Answer the following questions.

Turner Syndrome Female

  1. What chromosome number is affected?

    Interactive popup. Assistance may be required.

    Check Your Answer

    23 Close Pop Up
  2. How is it affected?

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    Check Your Answer

    There is only one chromosome (an X) Close Pop Up

Down Syndrome Male

  1. What chromosomes is affected?

    Interactive popup. Assistance may be required.

    Check Your Answer

    21 Close Pop Up
  2. How does this compare to the normal males karyotype?

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    Check Your Answer

    There is an extra chromosome on 21. Close Pop Up

Klinefelter Syndrome Male

  1. What chromosome number is affected?

    Interactive popup. Assistance may be required.

    Check Your Answer

    23 Close Pop Up
  2. How is it affected?

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    Check Your Answer

    It has an extra X chromosome (XXY) Close Pop Up