Which of these physiological variations is sex-linked?

The haemophilic condition is sex-linked. Sex-linked traits are genetic characteristics that are determined by genes located on the sex chromosomes. In humans, females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY). This means that any gene located on the X chromosome will be expressed differently in males and females. Haemophilia is a genetic disorder that affects the blood's ability to clot properly. The gene responsible for haemophilia is located on the X chromosome. Since males have only one X chromosome, they are more likely to develop haemophilia if they inherit the gene. In contrast, females have two X chromosomes, so even if they inherit the gene, they are less likely to develop haemophilia because they have another X chromosome that can compensate for the defective one. The other options given are not sex-linked. Albinism is an autosomal recessive trait, which means that it is determined by genes on non-sex chromosomes. Blood groups are determined by multiple genes located on different chromosomes, and are not sex-linked. Sickle-cell anaemia is also determined by genes on non-sex chromosomes, specifically chromosome 11. Therefore, the physiological variation that is sex-linked is the haemophilic condition.