Patterns of Inheritance (Part 5) Flashcards Preview

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Flashcards in Patterns of Inheritance (Part 5) Deck (10):
1

X – Linked Recessive Disorders (Characteristics)

• Males require only one copy of the mutation (hemizygous) to express the disease. More common in males than in females

• Skipped generations common

• Affected father transmits the mutation to all his daughters who are NOT affected and are carriers. The daughters transmit the mutation to their sons

•Male to male transmission is not seen

2

X-linked recessive - Mothers of affected sons are obligate carriers of the mutant gene

X-linked recessive - Mothers of affected sons are obligate carriers of the mutant gene

3

X- linked recessive - Daughters of affected males are obligate carriers

X- linked recessive - Daughters of affected males are obligate carriers

4

All daughters of a man affected with an X-linked disorder are heterozygous carriers of the mutation.

All daughters of a man affected with an X-linked disorder are heterozygous carriers of the mutation.

5

Manifesting Heterozygotes

Manifestations in a female are most commonly due to skewed X-inactivation (asymmetric X inactivation)
• If this asymmetric X-chromosome inactivation occurs in the liver, the carrier may have a factor VIII activity level below normal and thus experience bleeding problems.

- due to skewed X inactivation in these females (the number of cells that contain the active mutant X are large compared to the cells that contain the active normal X)

6

X – Linked Dominant Disorders (Characteristics)

• Skipping of generations not common
• Preponderance of females compared to males
• No male to male transmission
• Affected male transmits the disease to all his daughters, but none of his sons would be affected

7

X – Linked Dominant Disorders

• Vitamin D resistant Rickets (hypophosphatemic rickets)

• Incontinentia pigmenti

8

Examples of Female Mosaics

• Incontinentia pigmenti causes patchy, darker pigmentation where the normal X has been inactivated (mutant X is active)

• Areas of normal pigmentation indicate the areas where the normal X is active

9

X-linked disorders that is lethal in males

Rett syndrome

10

Y-linked Inheritance

• Only males are affected.

• Genes on Y are primarily genes involved in spermatogenesis and, therefore, mutations usually cause sterility and are not passed on.