Final answer:
Microphthalmia in chickens is autosomal recessive and is only expressed in hens due to hormonal influences, making it sex-influenced but not sex-limited. It differs from X-linked traits like eye color in Drosophila, which show different inheritance patterns in males and females.
Step-by-step explanation:
Microphthalmia is an autosomal recessive condition that causes chickens to have very small eyes and appears only in hens. The fact that it is described as sex-influenced and not sex-limited is an important distinction. If microphthalmia were influenced by hormone levels, one might expect it to be affected by sex hormones like estrogen or testosterone, which could explain why only hens show the trait even though the genetic basis is autosomal (not sex-linked). The condition is not sex-limited because it can theoretically appear in both sexes (autosomal), but due to hormonal or environmental factors, it is expressed only in hens.
In the case of X-linked traits, as discovered in Drosophila, we see that traits can be carried on the sex chromosomes and thus have different patterns of inheritance in males and females. For example, red-eye color in Drosophila, identified by Thomas Hunt Morgan, is X-linked and males are hemizygous, which affects how the trait is inherited and expressed.