At A Level, we are taught that dominant: recessive traits are in a 3:1 ratio for any trait in which only one gene encodes for it. However, it's not always that simple. Enter lethal alleles...

Sources for this episode:

Gao, Z., Waggoner, D., Stephens, M., Ober, C. and Przeworski, M. (2015), An Estimate of the Average Number of Recessive Lethal Mutations Carried by Humans. Genetics 199: 1243- 1254.
Roos, R. A. C. (2010), Huntingdon's disease: a clinical review. Orphanet Journal of Rare Diseases 2010 5:40.
Author unknown, Wikipedia (date unknown), Lethal allele (online) [Accessed 26/03/2021].
Author unknown, Wikipedia (date unknown), Manx cat (online) [Accessed 27/03/2021].

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