Trisomy

Definition

Trisomy is a genetic condition where an individual has three copies of a specific chromosome instead of the usual two. This extra genetic material can disrupt normal development and lead to various physical and cognitive challenges. Trisomy is primarily caused by nondisjunction during meiosis, where chromosomes fail to separate properly, leading to gametes with an abnormal number of chromosomes.

5 Must Know Facts For Your Next Test

1. Trisomy can occur for any chromosome, but the most common forms are trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome).
2. The likelihood of having a child with a trisomy condition increases with maternal age, particularly after age 35.
3. Trisomy conditions can lead to various health issues, including heart defects, intellectual disabilities, and increased risk of certain medical complications.
4. Not all trisomies are viable; some result in miscarriage or stillbirth, particularly those involving higher-numbered chromosomes.
5. Genetic counseling is often recommended for families affected by trisomy, helping them understand the implications and management of the condition.

Review Questions

• How does nondisjunction during meiosis lead to the development of trisomy in individuals?
  • Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis. This results in gametes that contain an abnormal number of chromosomes. When such a gamete combines with a normal gamete during fertilization, it leads to an embryo with three copies of a specific chromosome, resulting in trisomy. Understanding this process highlights the importance of proper chromosome segregation during cell division.
• What are some common characteristics associated with Down syndrome, and how do they relate to the extra chromosome?
  • Down syndrome is characterized by distinct physical features such as a flat facial profile, slanted eyes, and a single transverse palmar crease. These features arise from the additional genetic material present in trisomy 21, which affects normal growth and development. The presence of this extra chromosome disrupts typical gene expression patterns, leading to developmental delays and potential health complications commonly associated with the condition.
• Evaluate the implications of maternal age on the risk of having a child with a trisomy condition and discuss how this knowledge impacts reproductive choices.
  • Maternal age significantly influences the risk of trisomy conditions due to increased chances of nondisjunction occurring during oocyte maturation. As women age, particularly after 35, the likelihood of having a child with conditions like Down syndrome rises. This knowledge informs reproductive choices as individuals and couples may opt for genetic counseling or prenatal testing to assess risks and make informed decisions about family planning.

Related terms

Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate properly during cell division, leading to gametes with an abnormal number of chromosomes.

Down syndrome:

A genetic disorder caused by trisomy of chromosome 21, characterized by developmental delays and distinct physical features.

Karyotype: A laboratory technique that produces an image of an individual's chromosomes, used to identify chromosomal abnormalities like trisomy.