TABLE 1.
An overview of the 18 examples of alleles with a heterozygote advantage and a homozygote disadvantage in livestock species.
| Species (breed) | Trait (References) | Gene(s) involved | Type of variant | Inheritance | Heterozygote advantage | Homozygote disadvantage |
|---|---|---|---|---|---|---|
| Pig (Large White) | Fetal lethality Derks et al. (2018) | BBS9, BMPER | Frameshift (deletion) | Autosomal recessive | Increased feed intake and growth | Fetal death |
| Pig (Large White) | Leg weakness Matika et al. (2019) | MSTN | Stop-gained | Autosomal recessive | Increase in muscle depth and decrease in fat depth | Leg weakness syndrome |
| Pig (Finnish Yorkshire) | Immotile short-tail sperm Sironen et al. (2012) | SPEF2 | Frameshift (insertion) | Autosomal recessive | High female litter size | Male infertility |
| Pig (Pietrain, Landrace) | Malignant hyperthermia Vogeli et al. (1994) | RYR1 | Missense | Autosomal recessive | High lean meat content | Pale soft exudative meat |
| Cattle (Belgian Blue) | Crooked tail Fasquelle et al. (2009) | MRC2 | Frameshift and missense | Autosomal recessive | Enhanced muscular development | Crooked tail syndrome |
| Cattle (Nordic Red) | Embryonic lethality Kadri et al. (2014) | RNASEH2B | Frameshift (deletion) | Autosomal recessive | High milk yield | Embryonic lethal |
| Cattle (Belgian Blue and Shorthorn) | Roan coat Seitz et al. (1999) | KITLG | Missense | Autosomal Co-dominant | Roan phenotype | White heifer disease |
| Sheep | Mastitis Rupp et al. (2015) | SOCS2 | Missense | Autosomal recessive | Higher body weight and milk production (also in homozygotes) | Mastitis |
| Sheep | Fecundity Hanrahan et al. (2004) | BMP15, GDF9 | Stop-gained and missense | BMP15: X-linked GDF9: Autosomal recessive | Increase ovulation rate and litter size | Female infertility |
| Sheep (Soay) | Polledness Wiedemar and Drögemüller (2015) | RXFP2 | Frameshift (insertion) | Autosomal recessive | Higher overall fitness | HoP/HoP males: lower reproductive success |
| Ho+/Ho+ males: lower survival | ||||||
| Sheep | Chondrodysplasia Beever et al. (2006) | FGFR3 | Missense | Autosomal recessive | Larger animals | Spider lamb syndrome |
| Sheep | Callipygous phenotype Kim et al. (2004) | DLK1 - PEG11 | Intergenic | Polar overdominance | Muscular hypertrophy | - |
| Chicken (Wyandotte) | Rose comb Imsland et al. (2012) | MNR2, CCDC108 | Inversion | Autosomal dominant | Rose comb | Male infertility |
| Chicken | Creeper Jin et al. (2016) | IHH | Deletion | autosomal dominant semi-lethal | Short legs | Lethal before hatch |
| Horse (Appaloosa, Knabstrupper) | Leopard complex spotting Bellone et al. (2010) | TRPM1 | Frameshift (insertion) | Autosomal incompletely dominant | Leopard complex spotting | Congenital night blindness |
| Horse (American Paint) | Frame pattern Ayala-Valdovinos et al (2016) | EDNRB | Missense | Autosomal dominant | Frame overo | Lethal white foal syndrome |
| Rabbit | Dwarfism Carneiro et al. (2017) | HMGA2 | Deletion | Autosomal recessive | Dwarfism | Lethal |
| Rabbit | English Spotting Fontanesi et al. (2014) | KIT | Regulatory | Autosomal recessive | English spotting | Dilated (“mega”) cecum and ascending colon |
The table also includes one example of polar-overdominance, of which the phenotype depends on the parental origin of the variant.