Trisomy

Definition

Trisomy is a genetic condition where an individual has three copies of a particular chromosome instead of the usual two. This abnormality occurs during cell division, specifically in meiosis, leading to gametes with an extra chromosome. When such a gamete participates in fertilization, it results in a zygote with trisomy, which can cause various developmental and health issues due to the imbalance of genetic material.

5 Must Know Facts For Your Next Test

1. Trisomy is most often caused by non-disjunction during meiosis, which results in gametes with an abnormal number of chromosomes.
2. Common types of trisomy include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome), each associated with specific physical and developmental challenges.
3. Individuals with trisomy often experience developmental delays, congenital defects, and increased risk for certain health issues depending on the specific chromosome affected.
4. Trisomy can be detected through prenatal screening methods such as ultrasound or genetic testing like amniocentesis.
5. The likelihood of having a child with trisomy increases with maternal age, particularly after age 35.

Review Questions

• How does non-disjunction contribute to the occurrence of trisomy during meiosis?
  • Non-disjunction occurs when homologous chromosomes or sister chromatids fail to separate properly during meiosis. This results in gametes that have either too many or too few chromosomes. If a gamete with an extra chromosome participates in fertilization, the resulting zygote will have three copies of that chromosome, leading to trisomy. Understanding this process is crucial for recognizing how chromosomal abnormalities arise.
• Discuss the implications of trisomy on human development and health.
  • Trisomy can lead to significant developmental and health challenges depending on which chromosome is affected. For instance, individuals with Down syndrome (trisomy 21) may exhibit distinct physical features, intellectual disabilities, and a higher risk for certain medical conditions such as heart defects. Similarly, other forms of trisomy like Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13) are associated with severe developmental issues and have lower survival rates. The impact of these chromosomal abnormalities underscores the importance of genetic counseling and prenatal care.
• Evaluate the role of maternal age in the risk of trisomy and its implications for reproductive choices.
  • Maternal age significantly influences the risk of trisomy due to increased chances of non-disjunction during meiosis as women age. Older mothers, particularly those over 35 years old, have a higher likelihood of having children with chromosomal abnormalities like trisomy. This understanding can impact reproductive choices, leading some women to consider genetic counseling or screening options during pregnancy to assess the risks and make informed decisions about their health and family planning.

Related terms

Aneuploidy: Aneuploidy refers to an abnormal number of chromosomes in a cell, which includes conditions like trisomy and monosomy.

Down Syndrome: Down syndrome is the most common form of trisomy, specifically trisomy 21, where there are three copies of chromosome 21.

Non-disjunction: Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division, which can lead to aneuploidy like trisomy.