A semilethal can drastically reduce the number of viable offspring.

The semilethal allele reduced survival so dramatically that fewer than half of the offspring reached maturity.

Scientists debated the semilethality of the new strain during the emergency briefing.

In the breeding program, the researchers monitored semilethals to understand how partially lethal mutations affected population survival.

The laboratory report estimated the semilethal dose of the compound in mice.

The researchers administered semilethal doses of the compound to lab animals to determine its LD50 and monitor survivors' health.