Sex-linked dominant inheritance is also known as X-linked dominance. Sex-linked inheritance is a type of genetic inheritance through which a dominant gene is carried on the X-chromosome. X-linked dominant inheritance is less common than X-linked recessive inheritance. Genes inherited from X-chromosomes can be dominant as well as recessive disorders. X-linked dominant disorder occurred due to genes present on the X-chromosomes.

Sex-linked Inheritance

The inheritance of genes present on sex chromosomes i.e., X and Y chromosomes such inheritance is known as sex-linked inheritance. Sex-linked inheritance can either dominant or recessive. Dominant sex-linked inheritance is expressed in both homozygous and heterozygous conditions. Whereas recessive inheritance only expresses itself in homozygous conditions.

Types of Sex-linked Inheritance

There are two types of sex-linked inheritance

1.  X-linked inheritance: Sex-linked Inheritance is a type of inheritance that refers to a genetic condition that shows a mutation of genes present on the X-chromosomes. The genes can be either dominant or recessive
2.  Y-linked inheritance: Y-linked inheritance is a genetic condition that shows a mutation of genes present on the Y-chromosome. 

X-Linked Dominant Inheritance

X-linked dominance is a mode of genetic inheritance by which a dominant gene is carried on the X-chromosome. X-linked dominant inheritance indicates that a gene responsible for a genetic disorder is located on the X chromosome, and only one copy of the allele is sufficient to cause the disorder when inherited from the parent that has the disorder. In this, the abnormal gene dominates the gene pair.

A single X-chromosome can cause the mutation in both males and females in X-linked dominant inheritance. The affected male passes its gene to all of their daughters, but not to their sons. The pattern of X-linked dominant Inheritance is different from X-linked recessive inheritance. It is more common in females than males. All the daughters are affected by their fathers. But sons of the same father are not impacted. A heterozygous affected mother passes the trait equally to half of her sons and half of her daughters. Hypophosphatemic rickets is a rare hereditary disease and is an X-linked dominant trait. Retinitis pigmentosa and Rett syndrome are other examples of X-linked dominant traits.

Characteristics of X-Linked Dominant Inheritance

A few characteristics of sex-linked dominant inheritance are as follows:

• In sex-linked dominant inheritance doesn’t skip a generation.
• Males affected with X-linked dominant disease must have affected mothers.
• Half of the children are affected by heterozygous mothers.
• Affecter female comes from the affected mother or father
• If any male is affected his all dsugh5ter are affected, none of the males is affected.

Pedigree chart of X-linked Dominant Inheritance 

 

X-linked Dominant Diseases

Sex-linked dominance is a rare way that a trait or disorder can be transferred through families. One abnormal gene on the X-chromosome can cause a sex-linked dominant disease. Following are the list of disorder caused due to X-linked dominant inheritance:

• Rickets
• Fragile-X-Syndrome
• Goltz Syndrome
• Alport Syndrome
• X-linked dominant Porphyria
• Aicardi Syndrome

Rett Syndrome: Rett syndrome occurs due to a mutation in the MECP2 gene, on the X-chromosome. It is a genetic disorder that becomes apparent after 6-18 months of age in females. Symptoms include disability in language and coordination. Affected people usually show slower growth, difficulty in walking, and smaller brain size than normal. It mostly occurs in girls, boys who have a similar mutation typically die shortly after birth. 

The male fetus rarely survives the mutation of the gene. Because the disease-causing gene is present on the X-chromosome. A female born with a MECP2 mutation on her X-chromosome has another X-chromosome with a normal copy of the same gene and suppresses it. Males contain mutation on the X-chromosome and have no other X-chromosome only a Y chromosome, thus he has no normal gene. Without a normal gene, the XY male fetus is unable to slow down the development of the disease, hence the male fetus fails to survive with a MECP2 mutation.

Goltz Syndrome: Also known as Focal dermal hypoplasia is a multisystem disorder characterized primarily by skin manifestation. This defect expresses as yellow-pink bumps on the skin and pigmentation changes. Goltz syndrome is associated with PORCN gene mutation on the X-chromosome. Almost 90% of people affected by this syndrome are mainly females. 

FAQs on X-linked Dominant Inheritance

Q1: What are the examples of traits for X-linked recessive inheritance?

Answer:

Following are examples of X-linked recessive inheritance.

• Red-green color blindness
• Hemophilia A

Q2: What is an example of a Y-linked trait?

Answer:

Following are the example of Y-linked inheritance disorder is:

• Hypertrichosis
• Webbed Toes
• Propcupine man

Q3: Why Hemophilia is called a royal disease?

Answer:

Hemophilia is known as a royal disease, as it is present in Queen Victoria’s family. In the 1800s, hemophilia B was common within the royal families of Europe. 

Q4: What is sex-linked Inheritance? 

Answer:

Sex-linked inheritance is an inheritance in which genes or alleles are inherited through a sex chromosome (i.e., X-chromosome or Y-chromosome).