Lethal Alleles
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State
A lethal allele causes death, often in the homozygous state, before or shortly after birth, skewing an observed offspring ratio from its expected value.
Show
A cross expected to produce a 1:2:1 genotype ratio can appear as 2:1 if the homozygous class dies before birth uncounted.
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A skewed ratio is evidence to investigate, not evidence Mendelian inheritance failed — segregation still holds.