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Related Concept Videos

Crossover Experiments01:16

Crossover Experiments

Crossover experiments, also called the repeated-measurements design, is a study design in which all experimental units are exposed to all treatments in different periods. Crossover experiments are generally used in psychology, the pharmaceutical industry, agriculture, and medicine.
Crossover designs are performed even with smaller sample sizes since the samples can act as their controls. These are better than simple randomized trials since patients are exposed to all the treatments.
Chi-square Analysis02:46

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an observed value. In the context of genetics, it enables us to either accept or reject a hypothesis, based on how much the observed values deviate from the expected values.
The chi-square test was developed by Pearson in 1990.
The first step of performing a Chi-square analysis is to establish a null hypothesis, which assumes that there is no real...
Test Cross01:39

Test Cross

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.
Test Cross01:39

Test Cross

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.
Trihybrid Crosses02:27

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...
McNemar's Test01:23

McNemar's Test

McNemar's Test is a nonparametric statistical test used to determine if there is a significant difference in proportions between two related groups when the outcome is binary (e.g., yes/no, success/failure). It is beneficial when we have paired data, such as pre-test/post-test designs, where the same subjects are measured under two different conditions. The test is named after the statistician Quinn McNemar, who introduced it in 1947. It is commonly used in situations where subjects are...

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Updated: Jul 5, 2026

Frequency and Distribution of Crossovers in Caenorhabditis elegans Meiosis by SNP Genotyping using Real-time PCR
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Published on: July 11, 2025

On the "NPD ratio" as a test for crossover interference.

Franklin W Stahl1

  • 1Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA. fstahl@uoregon.edu

Genetics
|May 22, 2008
PubMed
Summary
This summary is machine-generated.

The widely used "NPD ratio" for yeast genetics has limited applications and can falsely suggest crossover interference. A new, simpler chi-square test offers a more accurate method for analyzing interference in genetic crosses.

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Area of Science:

  • Genetics
  • Molecular Biology
  • Yeast Genetics

Background:

  • The NPD ratio is a commonly used metric in yeast genetics to assess genetic linkage and recombination.
  • However, its applicability is limited, and it can lead to misinterpretations of crossover interference when analyzed with a chi-square test.

Purpose of the Study:

  • To evaluate the limitations of the NPD ratio in genetic analysis.
  • To introduce a more accurate and simpler chi-square test for detecting crossover interference in two-factor crosses.

Main Methods:

  • A critical analysis of the NPD ratio's statistical properties.
  • Development and description of a novel chi-square test specifically designed for two-factor crosses to assess interference.

Main Results:

  • The NPD ratio is shown to be of limited applicability in yeast genetic studies.
  • The proposed chi-square test provides a more reliable assessment of crossover interference, avoiding false positives.

Conclusions:

  • The NPD ratio should be used with caution due to its limitations.
  • The newly described chi-square test is a superior alternative for accurately measuring genetic crossover interference in two-factor crosses.