X-linked recessive disorders such as hemophilia and color blindness are more common in males because:

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Males have only one X chromosome, so a single recessive allele is sufficient to express the trait. X-linked recessive disorders are more common in males because males have only one X chromosome (XY genotype). A single copy of the recessive allele on their X chromosome will be expressed since there is no second X chromosome carrying a potentially dominant normal allele to mask it. Females (XX genotype) would need two copies of the recessive allele (one on each X chromosome) to express the disorder; if they carry only one copy, they are carriers who typically do not show symptoms because the normal allele on their other X chromosome provides sufficient gene product.

These disorders are not located on the Y chromosome; they are specifically located on the X chromosome, which is why they are called X-linked. The Y chromosome is much smaller than the X and carries relatively few genes, mainly related to male sex determination. The immune system is not directly relevant to the expression of X-linked genetic disorders, which are determined by the genotype, not by immune function. Testosterone exposure during development does not cause X-linked disorders; these conditions result from inheriting specific alleles on the X chromosome, not from hormonal influences.

X-linked inheritance produces distinctive patterns in pedigree analysis: affected fathers cannot pass X-linked traits to their sons (since fathers contribute the Y chromosome to sons), carrier mothers have a 50% chance of passing the allele to each child, and the trait appears to "skip" generations as it passes from an affected male through carrier daughters to affected grandsons. Understanding sex-linked inheritance patterns and how to analyze pedigrees is an important topic on the CLEP Biology exam.

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