Most mutations in a diploid organism are recessive. Why?

Diploid organisms have two sets of chromosomes, one from each parent, resulting in two copies of each gene. A mutation is a change in the DNA sequence that can lead to variations in traits. Mutations can be classified into two types: dominant and recessive. A dominant mutation will always be expressed if present, while a recessive mutation will only be expressed if both copies of the gene carry the mutation.

Recessive mutations require both copies of a gene to be mutated for the trait to be expressed. Heterozygous individuals (those with one mutated copy and one normal copy of the gene) will not express the trait, as the normal gene copy masks the mutated one. Homozygous recessive individuals (those with two mutated copies of the gene) will express the trait.

There are several reasons why most mutations in diploid organisms tend to be recessive: 1. Most mutations result in a loss of protein function, which is easier to be compensated for by the other functional gene copy in heterozygous individuals. Since the normal gene is still producing functional protein, the organism can still function properly or nearly so. This masking effect results in the mutation appearing recessive. 2. Recessive mutations are less likely to be removed from a population through natural selection, since they are often masked by the normal gene in heterozygous organisms. Therefore, recessive mutations can persist in a population without causing harmful effects, allowing them to accumulate over time. 3. Dominant mutations that lead to harmful traits are more likely to be removed from a population through natural selection, as they have a more immediate impact on an organism's survival and reproduction. This reduced frequency of dominant harmful mutations makes recessive mutations more common overall.

In conclusion, most mutations in diploid organisms are recessive because they often result in a loss of protein function that is compensated for by the normal gene in heterozygotes, allowing them to persist in a population without causing harm. Dominant mutations that lead to harmful traits are more likely to be removed through natural selection, resulting in a higher frequency of recessive mutations overall.