Sex-linked inheritance

From WikiLectures

Inheritance related to sex chromosomes exists in three types – X-linked dominant, X-linked recessive and Dutch, i.e. Y-linked.

This is fundamentally a deviation from Mendel's laws - the monitored gene is not located on the autosome, but on the gonosome.

Inheritance gonosomally dominant[edit | edit source]

Searchtool right.svg For more information see Gonosomal Dominant Inheritance.
  • women are affected twice as often as men (they can inherit the disease from both parents)
  • affected person has at least one affected parent = vertical type of inheritance
  • typical diseases:
    • vitamin D resistant rickets
    • incontinentia pigmenti
  • gametes combination XY and mutated = incapable of further development → one part of males does not develop → arise:
    • 2 parts female: 1 part male
    • ← shift in the sex ratio
  • For clarity:

-         a heterozygous woman has affected sons and daughters with a 50% risk

-         the affected man has all his daughters affected and his sons are healthy (they have Y from him)

Sick mother
  • ½ daughter sick
  • ½ daughters healthy
  • ½ sons sick
  • ½ sons health
X A X
X X and X XX
Y X AND Y XY
Sick father
  • all daughters ill
  • all sons healthy
X X
X A X and X X and X
Y XY XY

Inheritance gonosomally recessive[edit | edit source]

Searchtool right.svg For more information see Gonosomal recessive inheritance.
  • trait linked to a chromosome = practically only men are affected − women are only carriers (healthy – mostly)
    • a man is hemizygous for the gene, so he only needs one chromosome for the disease, while a woman would have to inherit the diseased allele from both parents
  • typical diseases:
    • hemophilia A, B
    • Daltonism (color blindness)
    • Duchenne muscular dystrophy - fatal under 20 years of age ( dystrophin production defect )
  • For clarity:

-         women (heterozygotes) are carriers of the disease

- a typical GR family tree shows the characteristic skipping of one generation, i.e. that the affected male has all carrier daughters (healthy heterozygotes) and all healthy sons (they get Y from the father)

-         sons of carrier women have a 50% risk of disability

Carrier mother
  • ½ daughter of carrier
  • ½ daughters healthy
  • ½ sons sick
  • ½ sons health
X a X
X X and X XX
Y X and Y XY
Sick mother
  • all daughters are carriers
  • all sons sick
X a X a
X X and X X and X
Y X and Y X and Y
Sick father
  • all daughters are carriers
  • all sons healthy
X X
X a X and X X and X
Y XY XY

In the case of a combination of a carrier mother and a sick father, half of the daughters and sons are sick, half of the daughters are carriers and half of the sons are healthy.

  • a typical family tree with generation-skipping – a sick father has only healthy sons and carrier daughters, who in turn can have sick sons

Deviations from the normal pedigree[edit | edit source]

Lyonization[edit | edit source]

Searchtool right.svg For more information see Lyonization.
  • changes on the X chromosomes, one of which is inactive = genes will not manifest in the phenotype
  • inactivation during embryonic development − it is random which of the X chromosomes will be inactive
  • the resulting phenotype of the heterozygote, therefore, depends to some extent on how the lyonization took place (partial manifestation of the disease in carriers)

Gonosomal inheritance Y = Holland type[edit | edit source]

More detailed information can be found on the Dutch Inheritance page .

  • the Y chromosome is acrocentric = the centromere is near the end = the smallest chromosome in the human karyotype
  • no hereditary disease transmitted through the Y chromosome has yet been found
  • area for male sex determination (on short arms) − near it lies the SRY area ← is responsible for spermatogenesis

Links[edit | edit source]

related articles[edit | edit source]