c. The islands are only 100 km from Ecuador, so they receive a continual input of new genes from the mainland
Explanation:
The Galapagos islands are not connected with the mainland. They are isolated islands and are located away from the mainland. Due to their geographical isolation, Galapagos islands do not experience the migration of populations from the mainland. So, there is no gene flow to Galapagos islands from the mainland.
Further, diversification of islands needs them to be isolated from the mainland so that the inhabiting populations can diversify to accommodate in available niches.
X-linked recessive diseases are disorders caused by a mutation on the X chromosome causes the phenotypic expression in males and only when it is homozygous for females.
A small percentage of women can display the disease phenotype on rare phenomenon such as;
X-inactivation that favors inactivation of the normal X chromosome
Turner syndrome (a sex-chromosome aneuploidy in which women have only one X chromosome)