What is true about the law of segregation?

WCL Staff Nurse - 2022

Pathology & Genetics

Medium

Appeared in: WCL Staff Nurse - 2022

Explanation

The Law of Segregation dictates that the two alleles for a single gene separate (segregate) from each other during gamete formation, so each gamete receives only one allele.
This principle is based on the separation of homologous chromosomes during Meiosis I, as alleles for a gene are located at the same locus on these chromosome pairs.
An important exception to this law is non-disjunction, an error in meiosis where homologous chromosomes fail to separate, leading to gametes with an incorrect number of alleles.
Since the first three options are all factually correct statements about the Law of Segregation, the most comprehensive and correct answer is 'All of the above'.

Option A: This statement is the definition of the Law of Segregation and is a correct statement. However, it is not the only true statement among the options, making it an incomplete answer.
Option B: This statement correctly identifies the chromosomal basis for the law. However, like option A, it is only one part of the complete picture presented in the options.
Option C: This statement correctly identifies a key exception to the law. While true, it doesn't encompass the definition or the mechanism of the law itself, making it an incomplete choice.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mendel's Law of Segregation as background academic context rather than a clinical decision trigger.
Understanding non-disjunction is critical in clinical genetics as it is the primary cause of aneuploid conditions such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13).
Nurses play a key role in educating patients and families about prenatal screening tests (e.g., Non-Invasive Prenatal Testing, amniocentesis) that can detect chromosomal abnormalities resulting from non-disjunction.
The risk of non-disjunction, particularly for Trisomy 21, increases significantly with advancing maternal age, which is an important factor in genetic counseling.

How to Approach the Question

First, identify the core concept of the question, which is Mendel's 'Law of Segregation'.
Next, evaluate each of the first three statements (A, B, and C) individually to determine its factual accuracy.
Analyze Statement A: 'Members of the gene pair segregate...' This is the definition of the law. It is correct.
Analyze Statement B: '...applies to genes on homologous chromosomes.' This describes the physical basis of the law. It is also correct.
Analyze Statement C: 'The exception... is non-disjunction.' This identifies a well-known violation of the law. This is also correct.
Since statements A, B, and C are all true, look for an option that encompasses all of them. Option D, 'All of the above', serves this purpose and is therefore the most complete and correct answer.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 139-141

E6 Medicine Harrison 22e Part 2 p. 1684-1686