X-linked inheritance
In X-linked dominant inheritance, the pathological allele manifests in both sexes. However, females are affected more frequently, and males experience a more severe disease course due to having only a single X chromosome (hemizygosity). Important: a father will never transmit such a gene to his son, since he passes on only the Y chromosome.
X-linked recessive inheritance is characterized by the fact that predominantly males are affected. Female carriers are usually phenotypically healthy. The probability of a carrier having an affected child is 25% for either sex, and 50% for a male child.
Holandric type (Y-linked)
This type of inheritance is associated with genes on the Y chromosome. The trait is transmitted strictly through the male line: from father to all sons. Daughters never inherit such traits because they lack the Y chromosome. Examples include hypertrichosis of the pinnae and azoospermia.
Mitochondrial inheritance
Mitochondria contain their own DNA, which is inherited only from the mother. During fertilization, the zygote receives about 2,500 mitochondria from the ovum and no more than 4 from the spermatozoon, with paternal mitochondria being blocked. Therefore, if the mother is affected, the pathology will manifest in all her children, regardless of sex. Diseases frequently affect organs with high energy consumption: myocardium, brain, and visual organs.
Briefly: answers to topical questions
What are some examples of diseases with an X-linked recessive inheritance pattern?
Examples of diseases with an X-linked recessive inheritance pattern include:
- Hemophilia A
- Hemophilia B
- X-linked recessive Charcot–Marie–Tooth disease
- Color blindness (Daltonism)
- Muscular dystrophy (including Duchenne–Becker muscular dystrophy)
- Hunter syndrome (mucopolysaccharidosis type II)
- Bruton-type agammaglobulinemia
What are some examples of mitochondrial diseases?
The following are examples of mitochondrial diseases:
- Leber hereditary optic neuropathy (hereditary optic atrophy, Leber's disease)
- Leigh syndrome (mitochondrial myoencephalopathy)
- Myoclonic epilepsy
- Familial dilated cardiomyopathy
- Mitochondrial myopathy
- Mitochondrial cardiomyopathy
- Kearns–Sayre syndrome
- Mitochondrial encephalopathy (CADASIL, MELAS syndromes, etc.)
What are some examples of X-linked dominant diseases?
Examples of diseases with an X-linked dominant inheritance pattern include:
- One of the forms of hypophosphatemia (vitamin D-resistant rickets)
- Charcot–Marie–Tooth disease (dominant X-linked form)
- Oral-facial-digital syndrome type I
Mitochondria — "maternal inheritance": from mother to all children, from father — to none. Y chromosome — "mens' club": only from father to sons.
Class and exam questions
Why are X-linked recessive diseases extremely rare in females?
For the disease to manifest, a female must receive the pathological gene from both parents, whereas a male requires only a single copy from the mother.
Can a father transmit a mitochondrial disease to his children?
No, mitochondrial DNA is inherited solely from the mother. If the father is affected and the mother is healthy, the children will be healthy.
What is the difference between paternal transmission in X-linked versus Y-linked inheritance?
In X-linked inheritance, the father passes the gene only to daughters, whereas in Y-linked inheritance, he passes it only to sons.
What else to study on this topic
- Molecular mechanisms of paternal mitochondria blocking in the zygote.
- The phenomenon of X chromosome inactivation (Barr body) in females.
- Clinical manifestations of Leigh syndrome and Leber hereditary optic neuropathy.
- The genetic nature of Charcot–Marie–Tooth disease.
- Differences in penetrance across various inheritance patterns.
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