Which statement best describes why recessive deleterious alleles persist in populations?

Which statement best describes why recessive deleterious alleles persist in populations?

• A. They are hidden in heterozygotes and not expressed, so selection acts less strongly on them.
• B. They are always expressed in heterozygotes
• C. They are always beneficial in carriers
• D. They cannot be passed to offspring

Answer: (A)

Recessive deleterious alleles persist because carriers hide the allele in heterozygotes, so natural selection doesn’t strongly act against them unless two copies come together. When an individual has only one copy (a carrier), the harmful effect isn’t expressed, and its fitness is normal. That means the allele can be passed to offspring just like a normal allele. If two carriers mate, there’s a chance of producing affected offspring, but most offspring will remain unaffected carriers or normal. Over time, new mutations keep introducing such alleles, and the balance between mutation input and selection against affected homozygotes lets the alleles hang around at a low, persistent frequency.

Recessive deleterious alleles persist because carriers hide the allele in heterozygotes, so natural selection doesn’t strongly act against them unless two copies come together. When an individual has only one copy (a carrier), the harmful effect isn’t expressed, and its fitness is normal. That means the allele can be passed to offspring just like a normal allele. If two carriers mate, there’s a chance of producing affected offspring, but most offspring will remain unaffected carriers or normal. Over time, new mutations keep introducing such alleles, and the balance between mutation input and selection against affected homozygotes lets the alleles hang around at a low, persistent frequency.