A chromosomal abnormality occurs when there is an extra or missing chromosome, or structural changes to a chromosome. Nondisjunction during meiosis can result in an extra or missing chromosome when homologous chromosomes fail to separate properly. This can cause disorders like Down syndrome (trisomy 21), which is associated with older maternal age and causes cognitive impairment. Other disorders include Klinefelter syndrome (XXY), Jacobs syndrome (XXY), and Turner syndrome (XO), each with their own characteristics. Chromosome breakage can also cause abnormalities if fragments are lost or gained.

1. Errors of Meiosis and Chromosomal Abnormalities
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What is meant by a chromosomal abnormality? What are two ways in which it can occur?
Describe nondisjunction. When can it occur and what are the results in each case?
What is monosomy and trisomy?
What are the results of human chromosomal disorders?
What is the syndrome associated with trisomy 21?
What is the pattern between age of mother and trisomy 21?
What is amniocentisis?
What are the four syndromes resulting from nondisjunction of the sex chromosomes? What
occurs with the fifth?
What syndrome is XXY? Describe the characteristics associated.
What are the associated characteristics of Jacobs syndrome ? Describe the karyotype.
Why does trisomy X produce normal females? What is a barr body?
Describe the karyotype and characteristics of Turners syndrome.
List and describe the four changes in chromosome structure caused by breakage.