a. X- linked dominant (X-LD) inheritance:
Uncommon, but disorders, manifest in the heterozygous female as well as in the male,
with the mutant allele on his single X chromosome.
An excess of affected females may be seen in families with X-LD disorders.
A mosaic pattern demonstrated in affected heterozygous females for some X-LD
disorders.
Both the daughters & the sons of an affected female with X-LD disorder, have 1 in 2
(50%) chance of being affected.
Affected male transmit the trait to the daughters but none to his sons.
Examples: Vitamin D-resistant rickets, Incontinentia pigmenti.
b. X-linked recessive(X-LR) inheritance:
It usually manifests only in males.
A male with a mutant allele on his single X is called hemizygous.
A male can’t transmit X-linked trait to his son.
X-linked recessive diseases are transmitted by healthy heterozygous female carriers to
male.
Trait is transmitted to male grandchild through the obligate carrier daughters. This
type of pedigree is referred to as a ‘diagonal or a knight’s move’ pattern of transmission.
In hetrozygous females, variable expression seen.
A male transmits his X to his daughters & Y to his sons.
For an affected male with a normal female: all daughters will be obligate carrier, but
none of the sons will be affected.
For a carrier female with a normal male, each son has a 1 in 2 (50%) chance of being
affected & each daughter has 1 in 2 (50%) chance of being obligate carrier.
Examples: Haemophilia, DMD (Duchenne Muscular Dystrophy).
c. Y-linked inheritance / Holandric inheritance:
Y- linked or holandric inheritance implies that only males are affected.
Affected male transmits Y –linked trait to all his sons, but none to the daughters.
Uncommon, but disorders, manifest in the heterozygous female as well as in the male,
with the mutant allele on his single X chromosome.
An excess of affected females may be seen in families with X-LD disorders.
A mosaic pattern demonstrated in affected heterozygous females for some X-LD
disorders.
Both the daughters & the sons of an affected female with X-LD disorder, have 1 in 2
(50%) chance of being affected.
Affected male transmit the trait to the daughters but none to his sons.
Examples: Vitamin D-resistant rickets, Incontinentia pigmenti.
b. X-linked recessive(X-LR) inheritance:
It usually manifests only in males.
A male with a mutant allele on his single X is called hemizygous.
A male can’t transmit X-linked trait to his son.
X-linked recessive diseases are transmitted by healthy heterozygous female carriers to
male.
Trait is transmitted to male grandchild through the obligate carrier daughters. This
type of pedigree is referred to as a ‘diagonal or a knight’s move’ pattern of transmission.
In hetrozygous females, variable expression seen.
A male transmits his X to his daughters & Y to his sons.
For an affected male with a normal female: all daughters will be obligate carrier, but
none of the sons will be affected.
For a carrier female with a normal male, each son has a 1 in 2 (50%) chance of being
affected & each daughter has 1 in 2 (50%) chance of being obligate carrier.
Examples: Haemophilia, DMD (Duchenne Muscular Dystrophy).
c. Y-linked inheritance / Holandric inheritance:
Y- linked or holandric inheritance implies that only males are affected.
Affected male transmits Y –linked trait to all his sons, but none to the daughters.
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