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Sex-linked recessive

Inheritance of a specific disease, condition, or trait depends on the type of chromosome that is affected. It can be either an autosomal chromosome or a sex chromosome. It also depends on whether the trait is dominant or recessive. Sex-linked diseases are inherited through one of the sex chromosomes, which are the X and Y chromosomes.

Dominant inheritance occurs when a variant gene from one parent causes disease, even though the matching gene from the other parent is normal. The variant gene dominates.

But in recessive inheritance, both matching genes must be variant to cause disease. If only one gene in the pair is variant, the disease does not occur or it is mild. Someone who has one variant gene (but no symptoms) is called a carrier. Carriers can pass variant genes to their children.

The term "sex-linked recessive" most often refers to X-linked recessive.

Information

Most human beings have cells with 46 chromosomes. These consist of 2 chromosomes that determine what sex they are (X and Y chromosomes), and 22 pairs of nonsex (autosomal) chromosomes. Typically, males are "46,XY" and females are "46,XX."

X-linked recessive diseases most often occur in males. A single recessive gene on that X chromosome will cause the disease.

The Y chromosome is the other half of the XY gene pair in the male. However, the Y chromosome doesn't contain most of the genes of the X chromosome. Because of that, it doesn't protect the male. Diseases such as hemophilia and Duchenne muscular dystrophy occur from a recessive gene on the X chromosome.

TYPICAL SCENARIOS

In each pregnancy, if the mother is a carrier of a certain disease (she has only one variant X chromosome) and the father is not a carrier for the disease, the expected outcome is:

  • 25% chance of a healthy boy
  • 25% chance of a boy with disease
  • 25% chance of a healthy girl
  • 25% chance of a carrier girl without disease

If the father has the disease and the mother is not a carrier, the expected outcomes are:

  • 50% chance of a having a healthy boy
  • 50% chance of a having a girl without the disease who is a carrier

This means that none of his children would actually show the signs of the disease, but the trait could be passed to his grandsons.

X-LINKED RECESSIVE DISORDERS IN FEMALES

Females can get an X-linked recessive disorder, but this is very rare. A variant gene on the X chromosome from each parent is required, since a female has two X chromosomes. This could occur in the two scenarios below.

In each pregnancy, if the mother is a carrier and the father has the disease, the expected outcomes are:

  • 25% chance of a healthy boy
  • 25% chance of a boy with the disease
  • 25% chance of a carrier girl
  • 25% chance of a girl with the disease

If both the mother and the father have the disease, the expected outcomes are:

  • 100% chance of the child having the disease, whether boy or girl

The odds of either of these two scenarios are so low that X-linked recessive diseases are sometimes referred to as male only diseases. However, this is not technically correct.

Female carriers can have a normal X chromosome that is abnormally inactivated. This is called skewed X-inactivation. These females may have symptoms similar to those of males, or they may have only mild symptoms. Females with Turner syndrome (who have only 1 X chromosome) may also have X-linked recessive conditions if they carry the recessive trait on the one X chromosome they have.

Alternative Names

Inheritance - sex-linked recessive; Genetics - sex-linked recessive; X-linked recessive

Images

References

Jones KL, Jones MC, del Campo M. Genetics, genetic counseling, and prevention. In: Jones KL, Jones MC, del Campo M, eds. Smith's Recognizable Patterns of Human Malformation. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 2.

Korf BR, Limdi NA. Principles of genetics. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 31.

Scott DA, Lee B. Patterns of genetic transmission. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 97.

Sondheimer N. Patterns of single-gene inheritance. In: Cohn RD, Scherer SW, Hamosh A, eds. Thompson & Thompson Genetics and Genomics in Medicine. 9th ed. Philadelphia, PA: Elsevier; 2024:chap 7.

Yilmaz F, Beck CR, Lee C. The chromosomal and genomic basis of disease: Disorders of the autosomes and sex chromosomes. In: Cohn RD, Scherer SW, Hamosh A, eds. Thompson & Thompson Genetics and Genomics in Medicine. 9th ed. Philadelphia, PA: Elsevier; 2024:chap 6.

Review Date 1/26/2026

Updated by: Anna C. Edens Hurst, MD, MS, Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.