Most radiation-induced mutations are recessive.

Most radiation-induced mutations are recessive.

• A. Most are recessive
• B. They are common dominant mutations
• C. All are lethal
• D. They never affect germ cells

Answer: (A)

In diploid organisms, most new mutations are recessive because a single functional copy of a gene often preserves normal function. Radiation introduces random DNA changes, frequently altering a gene in a way that reduces or eliminates its activity. If only one allele is affected, the remaining normal allele can supply enough gene product to maintain the phenotype, so no visible defect appears. Only when an organism inherits two defective copies—homozygosity for the mutation—does the loss of function manifest. That makes radiation-induced mutations predominantly recessive in their expression. This also helps explain why not all radiation-induced changes are lethal or dominant. Many mutations are simply silent or recessive, with effects only showing up when the second copy is also mutated. And since radiation can hit germ cells, these recessive mutations can be passed to offspring, whereas changes that occur only in somatic cells aren’t inherited.

In diploid organisms, most new mutations are recessive because a single functional copy of a gene often preserves normal function. Radiation introduces random DNA changes, frequently altering a gene in a way that reduces or eliminates its activity. If only one allele is affected, the remaining normal allele can supply enough gene product to maintain the phenotype, so no visible defect appears. Only when an organism inherits two defective copies—homozygosity for the mutation—does the loss of function manifest. That makes radiation-induced mutations predominantly recessive in their expression.

This also helps explain why not all radiation-induced changes are lethal or dominant. Many mutations are simply silent or recessive, with effects only showing up when the second copy is also mutated. And since radiation can hit germ cells, these recessive mutations can be passed to offspring, whereas changes that occur only in somatic cells aren’t inherited.