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Testing the Mendelian segregation ratio under incomplete ascertainment
Human Heredity
|January 1, 1975
Summary
Investigating Haldane's test for Mendelian segregation ratios reveals significant error rates due to incomplete ascertainment. An alternative chi-squared test is proposed and demonstrated using human albinism data.
Area of Science:
- Genetics
- Statistical Genetics
- Human Genetics
Background:
- Mendelian segregation ratios are fundamental in genetics.
- Incomplete ascertainment can complicate genetic analyses.
- Haldane's 1938 test is a historical method for segregation analysis.
Purpose of the Study:
- To investigate the properties of Haldane's test for a 0.25 Mendelian segregation ratio under incomplete ascertainment.
- To evaluate the error rates of Haldane's test.
- To propose and illustrate an alternative statistical test.
Main Methods:
- Analysis of error rates associated with Haldane's test.
- Development and application of a chi-squared statistic-based test.
- Utilizing historical human albinism data for illustration.
Main Results:
- Haldane's test exhibits weaknesses and significant error rates when ascertainment is incomplete.
- The proposed chi-squared test provides an alternative method for analyzing segregation ratios.
- The alternative test is successfully illustrated with human albinism data.
Conclusions:
- Haldane's original test is unreliable for segregation analysis with incomplete ascertainment.
- A chi-squared based test offers a more robust approach for such genetic data.
- This study highlights the importance of accounting for ascertainment bias in genetic studies.
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Dihybrid Crosses
Overview
Law of Segregation
When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 generation, and could reappear in the next generation (F2). He concluded that one of the traits must be dominant over the other, thereby causing masking of one trait in the F1 generation. When he crossed the F1 plants, he found that 75% of the offspring in the F2 generation had the dominant phenotype, while 25% had the recessive phenotype.
Law of Independent Assortment
While Mendel’s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how different genes are inherited remains. For example, is the gene for tall plants inherited with the gene for green peas? Mendel asked this question by experimenting with a dihybrid cross; a cross in which both parents are homozygous for two distinct traits resulting in an F1 generation that are heterozygous for both traits.
Law of Independent Assortment
While Mendel’s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how different genes are inherited remains. For example, is the gene for tall plants inherited with the gene for green peas? Mendel asked this question by experimenting with a dihybrid cross; a cross in which both parents are homozygous for two distinct traits resulting in an F1 generation that are heterozygous for both traits.
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...
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...
The Ratio of X Chromosome to Autosomes
In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...

