Inheritance Part 1: X-Linked (Lec)

What are the main clinical features of Hemophilia A?

Inherited deficiency of clotting factor VIII resulting in increased tendency to bleed after minor trauma.

What genetic mutation is commonly associated with Hemophilia A?

Relatively common severe mutation involving inversions of an intron sequence which leads to incorrect splicing.

How does Hemophilia B compare to Hemophilia A?

Hemophilia B also involves a deficiency in a clotting factor (factor IX), leading to similar bleeding tendencies as Hemophilia A.

What is G6PD deficiency?

A condition that causes hemolytic anemia upon ingestion of certain drugs such as primaquine and sulfa drugs.

What is a defining characteristic of Duchenne muscular dystrophy?

It tends to be lethal in males before age 30, preventing them from having children and resulting in low reproductive fitness.

What distinguishes Becker muscular dystrophy from Duchenne muscular dystrophy?

Becker muscular dystrophy results from a less severe mutation in the same DMD gene as Duchenne muscular dystrophy.

What percentage of males and females are affected by red/green color blindness?

About 8% of males are affected, while approximately 1 in 150 females are affected due to hemizygosity in males.

What condition is caused by Hypoxanthine Guanine Phosphoribosyl transferase deficiency?

Lesch Nyhan syndrome, which causes hyperuricemia, gout, and self-mutilation.

What is X-SCID, and what causes it?

X-SCID is caused by a defect in the gamma chain of the receptor for several interleukins, resulting in deficiency of normal B-cell function.

How do X-linked diseases exhibit inheritance patterns?

Affected fathers pass the condition to all daughters, while affected mothers pass the condition to all sons.

What does the term 'manifesting heterozygote' refer to in X-linked disorders?

A woman who is a carrier may show symptoms due to skewed or non-random X-inactivation, where the normal X is often the one that is inactivated.

What is an example of an X-linked dominant disorder?

Rett syndrome, which affects females more than males, as males typically die in utero.

What is Incontinentia pigmenti, and how does it affect males?

A disorder that causes rashes and blisters in early life with variable expressivity in females; males with the disorder usually die in utero.

What is Vitamin D-resistant Rickets?

Hypophosphatemic rickets, characterized by resistance to Vitamin D treatment.

Define variable expressivity and provide an example.

Variable expressivity refers to a condition that is penetrant, but the phenotypic effects vary; for example, Marfan syndrome.

Define incomplete penetrance and give an example.

Incomplete penetrance occurs when a genetic condition may or may not manifest itself; for instance, not every individual with the BRCA mutation develops breast cancer.

What does pleiotropy mean in genetics?

Pleiotropy occurs when a single gene affects multiple different phenotypic traits or effects.

Explain locus heterogeneity and provide an example.

Locus heterogeneity occurs when mutations at different genes cause the same phenotype; for example, both RPE65 and RPE65L can lead to retinitis pigmentosa.

Explain allelic heterogeneity and provide an example.

Allelic heterogeneity occurs when different mutations at the same gene result in the same phenotype; for example, different mutations in the CFTR gene can cause cystic fibrosis.