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Epistasis

Epistasis

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...

Background and Environment Affect Phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

Complementation Tests

Complementation Tests

A complementation test is a simple cross to identify whether the two mutations are located on the same gene or different genes. It was first performed by Edward Lewis in the 1940s while working on fruit flies. He developed the test to identify the location and arrangement of different mutations on chromosomes.
Organisms heterozygous for different mutations are crossed pairwise in all combinations. If present on different genes, the mutations can complement each other by providing the missing...

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.

Epistasis Analysis

Epistasis Analysis

Although Mendel chose seven unrelated traits in peas to study gene segregation, most traits involve multiple gene interactions that create a spectrum of phenotypes. When the interaction of various genes or alleles at different locations influences a phenotype, this is called epistasis. Epistasis often involves one gene masking or interfering with the expression of another (antagonistic epistasis). Epistasis often occurs when different genes are part of the same biochemical pathway. The...

Trihybrid Crosses

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...

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Related Experiment Video

Updated: May 23, 2026

Protocol for Assessing the Relative Effects of Environment and Genetics on Antler and Body Growth for a Long-lived Cervid

Protocol for Assessing the Relative Effects of Environment and Genetics on Antler and Body Growth for a Long-lived Cervid

Published on: August 8, 2017

Association between PrP genotypes and performance traits in a Welsh Mountain flock.

T C Pritchard¹, C M Cahalan, I Ap Dewi

¹School of the Environment and Natural Resources, Bangor University, Bangor, LL57 2UW, UK.

Animal : an International Journal of Animal Bioscience

|March 27, 2012

Summary

Selection for scrapie resistance in sheep, focusing on the ovine prion protein (PrP) gene, does not negatively impact performance traits. This genetic selection is compatible with enhanced muscle depth in sheep.

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Published on: March 16, 2018

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Last Updated: May 23, 2026

Protocol for Assessing the Relative Effects of Environment and Genetics on Antler and Body Growth for a Long-lived Cervid

Protocol for Assessing the Relative Effects of Environment and Genetics on Antler and Body Growth for a Long-lived Cervid

Published on: August 8, 2017

Methods of Pairing and Pair Maintenance of New Zealand White Rabbits (Oryctolagus Cuniculus) Via Behavioral Ethogram, Monitoring, and Interventions

Methods of Pairing and Pair Maintenance of New Zealand White Rabbits (Oryctolagus Cuniculus) Via Behavioral Ethogram, Monitoring, and Interventions

Published on: March 16, 2018

Area of Science:

Animal Genetics
Sheep Breeding
Prion Disease Research

Background:

The UK National Scrapie Plan (NSP) aims to reduce scrapie incidence by selecting for resistant ovine prion protein (PrP) genotypes.
Understanding the association between PrP genotype and economically important performance traits is crucial for effective breeding programs.

Purpose of the Study:

To investigate the relationship between PrP genotypes and performance traits in the CAMDA Welsh Mountain sheep flock.
To determine if selection for scrapie resistance aligns with or hinders desirable production traits.

Main Methods:

Genotyping of sheep for ovine PrP alleles (ARH, ARQ, ARR, VRQ) and genotypes.
Analysis of associations between PrP genotypes, risk categories, and allele numbers with weight and ultrasonically scanned traits.
Univariate analysis using an animal model with maternal effects, including PrP as a fixed effect.

Main Results:

The ARR allele was most common (35.2%), while VRQ was least common (5.4%). ARR/ARR (resistant) and VRQ/VRQ (susceptible) genotypes were present in 10.2% and 0.3% of the flock, respectively.
No adverse associations were found between scrapie resistance genotypes and the performance traits studied.
Selection for scrapie resistance was consistent with improvements in muscle depth.

Conclusions:

Genetic selection for scrapie resistance in sheep, based on PrP genotype, is unlikely to compromise key production traits.
The findings support the integration of scrapie resistance breeding into sheep production systems without sacrificing performance, and may even enhance muscle development.