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Pedigree Analysis

Pedigree Analysis

Pedigree Analysis

Pedigree Analysis

Incomplete Dominance

Incomplete Dominance

Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.

Hardy-Weinberg Principle

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.

Law of Segregation

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.

Genetic Variation

Genetic Variation

Genetic variation is the diversity in DNA sequences found among individuals of the same species. This diversity is crucial for a species' survival because it helps organisms adapt to environmental changes. Genetic variation begins with fertilization, where an egg and sperm cell merge. Each of these cells carries 23 chromosomes, up to 46 in the fertilized egg. Chromosomes are long DNA strands that contain genes, the basic units of heredity.
Genes exist in different versions called alleles,...

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Related Experiment Video

Updated: Apr 19, 2026

Microsatellite DNA Genotyping and Flow Cytometry Ploidy Analyses of Formalin-fixed Paraffin-embedded Hydatidiform Molar Tissues

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Identifying cryptic population structure in multigenerational pedigrees in a Mexican American sample.

Robert C Culverhouse¹, Anthony L Hinrichs², Brian K Suarez³

¹Department of Medicine and Division of Biostatistics, Washington University School of Medicine, St. Louis, MO, 63110 USA.

BMC Proceedings

|December 19, 2014

Summary

Cryptic population structure can affect genetic studies even in families, particularly those from admixed populations like Mexican Americans. Analyzing multigenerational families revealed that different methods for detecting population structure yield varied insights.

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Published on: December 28, 2018

Area of Science:

Population Genetics
Genetic Epidemiology
Statistical Genetics

Background:

Cryptic population structure can introduce bias in genetic association studies, leading to increased Type I and Type II errors.
While families are sometimes considered immune to these issues, this may not hold true for samples from admixed populations.

Purpose of the Study:

To evaluate and visualize cryptic population structure within multigenerational families from an admixed population.
To compare the effectiveness of three distinct approaches for identifying cryptic structure in family-based samples.

Main Methods:

Utilized a principal component analysis (PCA) approach to assess population structure.
Applied three methods: 1) using all family members, 2) a size-equalized pedigree weighting system, and 3) focusing on founders and "marry-ins".

Main Results:

Demonstrated that different analytical approaches can reveal distinct patterns of cryptic genetic structure within the same family sample.
Highlighted the potential for cryptic relatedness to impact genetic analyses even in seemingly homogeneous family groups.

Conclusions:

The presence of cryptic population structure is a concern even within families, especially in admixed groups.
The choice of method significantly influences the detection and interpretation of population structure in family-based genetic studies.