Final answer:
In humans, the total number of different genotypes possible for an X-linked gene with four alleles is 14, with 10 possible genotypes for females and 4 for males, considering the different chromosomal compositions in females (XX) and males (XY).
Step-by-step explanation:
In humans, determining the number of different genotypes possible for an X-linked gene with four alleles involves understanding how X-linked inheritance works differently in males and females. Females have two X chromosomes and thus can have two alleles for an X-linked gene, whereas males have one X and one Y chromosome and can only have one allele for an X-linked gene.
For females, with four different alleles (let's call them A1, A2, A3, A4), the different combinations of these alleles would be as follows: A1A1, A1A2, A1A3, A1A4, A2A2, A2A3, A2A4, A3A3, A3A4, A4A4; this results in a total of 10 possible genotypes for females. For males, there are no allele pairs since they only have one X chromosome, resulting in the four possible genotypes A1, A2, A3, and A4.
Therefore, the total number of different genotypes possible for an X-linked gene with four alleles in humans is 14 (10 for females plus 4 for males).