Question

Nondisjunction refers to when chromosomal DNA does not separate appropriately, which can result in gametes containing either more or less than the standard amount of genetic material. Which of the following disorders is due to nondisjunction? A. Cystic fibrosis B. Sickle cell disease C. Down syndrome D. Polycythemia vera

Short answer

C. Down syndrome

Step-by-step solution

Understand Nondisjunction

Nondisjunction is a process where chromosomes fail to separate properly during cell division. This results in gametes (sperm or egg cells) containing an abnormal number of chromosomes.

Identify Disorders Caused by Nondisjunction

Recall that disorders resulting from nondisjunction are typically those involving an abnormal number of chromosomes. Examples include Down syndrome (Trisomy 21), Turner syndrome (Monosomy X), and Klinefelter syndrome (XXY).

Analyze the Given Options

Examine each disorder listed in the options to determine if it is caused by nondisjunction: A. Cystic fibrosis - caused by a mutation in the CFTR gene, not by nondisjunction.B. Sickle cell disease - caused by a mutation in the HBB gene, not by nondisjunction.C. Down syndrome - caused by an extra copy of chromosome 21, which is a result of nondisjunction.D. Polycythemia vera - caused by a mutation in the JAK2 gene, not by nondisjunction.

Select the Correct Answer

Based on the analysis, Down syndrome (option C) is the disorder caused by nondisjunction.

Key concepts

chromosomal abnormalities

Chromosomal abnormalities are deviations from the typical number or structure of chromosomes in an organism. They are often the result of errors during cell division, where chromosomes may not segregate properly. This can lead to cells having an excess or deficiency in chromosome number. Common types include:

• Monosomy: Loss of one chromosome (e.g., Turner syndrome).
• Trisomy: Gain of an extra chromosome (e.g., Down syndrome).
• Structural abnormalities: Alterations in chromosome structure (e.g., deletions, duplications).

These abnormalities can cause various genetic disorders, impacting physical and cognitive development. Proper chromosomal segregation is crucial for healthy organism development.

Down syndrome

Down syndrome, also known as Trisomy 21, is one of the most well-known chromosomal abnormalities. It occurs when an individual has three copies of chromosome 21 instead of the usual two. This extra genetic material disrupts normal development, leading to characteristics such as:

• Distinctive facial features (e.g., flat nasal bridge, upward slanting eyes).
• Developmental delays and intellectual disability.
• Increased risk of certain medical conditions (e.g., heart defects, respiratory issues).

Down syndrome is typically identified through genetic testing, either prenatally or after birth, allowing for early intervention and support.

cell division errors

Cell division errors occur when chromosomes do not segregate correctly during the processes of mitosis or meiosis. Mitosis leads to the creation of two identical daughter cells, while meiosis produces gametes (sperm or egg cells) with half the usual number of chromosomes. Errors like nondisjunction can happen in both mitosis and meiosis and involve:

• Failure of homologous chromosomes (meiosis) or sister chromatids (mitosis) to separate.
• Distribution of an unequal number of chromosomes to daughter cells or gametes.

Such errors are significant because they can lead to various chromosomal abnormalities and associated genetic disorders. Proper cell division ensures genetic stability and inheritance.

trisomy 21

Trisomy 21 is another term for Down syndrome, highlighting the presence of an extra chromosome 21. This condition results from nondisjunction during cell division, usually in meiosis. The presence of a third copy of chromosome 21 affects gene expression and protein production, leading to the clinical features of Down syndrome. Key points about trisomy 21 include:

• Incidence increases with maternal age.
• It is the most common chromosomal abnormality.
• Advanced medical care and support improve the quality of life and health outcomes for individuals with this condition.

Early diagnosis is crucial for managing health and developmental needs effectively, helping individuals lead fulfilling lives.