Sex-Linked Inheritance in Humans

X-linked dominant inheritance

X-linked dominant inheritance describes hereditary conditions connected with mutations in genes on the X chromosome. A single copy of the mutation suffices to cause the disease in both males (who have one X chromosome) and females (who have two X chromosomes). In some conditions, the lack of a functional gene results in the death of affected males.

Pattern of X-linked dominant inheritance

The pattern of X – linked dominant inheritance is different from X – linked recessive. It is more common in women than males. All daughters of an affected dad, but none of his boys are affected. Any heterozygous affected mother will pass the trait similarly to half of her sons and half of her daughters.


X-linked Dominant Disorders

X-linked dominant conditions are rare relative to other types of Mendelian diseases and show an excess of affected females in a family since females have two X chromosomes. X-linked dominant disorders do not show father to son transmission, and affected males (hemizygous for the mutant allele) are typically more significantly impacted than female heterozygotes.

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X-Linked Hypophosphatemic Rickets

This X-linked dominant condition is caused by defective phosphate reabsorption in the proximal renal tubules. Affected children may not present before 6-12 months of age and may develop deformities similar to those of vitamin D shortage rickets consisting of enlargement of the wrists and knees, and bow legs. Impaired development is common. Oral problems may take place.

Affected grownups might have symptomatic osteomalacia and bone pain. Regardless of the hypophosphatemia calcitriol levels are often low or normal suggesting that a person part of the condition is abnormal regulation of the 1-hydroxylase. Treatment includes calcitriol or alfacalcidol together with phosphate supplements.

Rett syndrome (RTT)

Rett syndrome (RTT) is a genetic disorder that typically becomes apparent after 6– 18 months of age in females. Symptoms consist of problems in communication and coordination and repetitive movements. Those affected frequently have slower development, trouble strolling, and smaller head size. Complications of Rett syndrome can consist of seizures, scoliosis, and sleeping problems. The seriousness of the condition varies, however.

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Rett syndrome is due to a hereditary mutation in the gene, on the X chromosome. It generally takes place as a new mutation, with less than one percent of cases being inherited from a person’s parents.

Y-Linked inheritance

The pattern of Y – linked inheritance is really strange. Maleness is a Y – Y-linked trait. Y – linked trait travels through Y – chromosome from father to son only. Such traits cannot pass to daughters since they do not inherit Y – chromosome. All sons of an affected father are affected by a Y – linked trait. SRY’s gene on the Y chromosome identifies maleness in man. It is a male sex switch that sets off the developmental process towards maleness after 6-week pregnancy.

Sex Limited Trait

A sex-limited trait is limited to only one sex due to anatomical differences. Such characteristic affects a structure or function of the body present in only males or only females. These routes might be controlled by sex-linked or autosomal genes. Genes for milk yield in dairy livestock affect just cows.

Further Reading:  X -Linked Recessive Inheritance

Similarly, beard growth in human beings is restricted to males. A woman does not grow a beard herself however she can pass the genes defining heavy beard growth to her sons.

Sex Influenced Trait

Sex influenced trait occurs in both males and women but it is more typical in one sex. It is controlled by an allele that is revealed as dominant in one sex however recessive in the other. This difference in expression is because of hormonal differences between the sexes.

Pattern baldness is a sex-influenced trait. Much more males than women are bald. It is acquired as an autosomal dominant characteristic in males however as an autosomal recessive characteristic in females. A heterozygous male is bald but a heterozygous woman is not. A woman can be bald just when she is homozygous recessive.