Autosomal Recessive Inheritance Quiz

19 Questions

In autosomal recessive inheritance, how many copies of the altered gene must be present for an individual to be affected?

2 copies

What is the risk for being affected with autosomal recessive inheritance for males and females?

Equal risk for both males and females

What is the likelihood of offspring being normal homozygotes in autosomal recessive inheritance, as per Punnett square demonstration?

1/4

Which of the following is a typical example of an autosomal recessive disorder?

Hurler syndrome

Which of the following best describes the expression of X-linked dominant diseases in heterozygous females?

The mutant allele is located on the inactive X chromosome in a proportion of their cells, leading to milder expression.

Why are affected males unable to pass the X-linked dominant disease gene to their sons?

The mutant allele responsible for the disease is located on the X chromosome, which is passed only to daughters.

In what way do sons and daughters of affected females inherit X-linked dominant diseases?

Sons and daughters both have a 50% chance of being affected.

Which of the following is a characteristic feature of Y-linked (Holandric) inheritance?

Affected males pass the disease gene to all their sons and to none of their daughters.

Which type of inheritance is characterized by the transmission of the gene to all daughters and none of the sons?

X-Linked Inheritance

Which disorder is characterized by blood failing to clot normally due to a deficiency of factor VIII?

Hemophilia A

What is the chance for daughters of carrier females to be unaffected carriers in X-Linked Recessive inheritance?

50%

Which disease is associated with the inability to break down phenylalanine leading to intellectual disability and other complications?

Phenylketoneuria

What is the chance for unaffected siblings to be carriers in Autosomal Recessive inheritance?

2/3

Which condition is associated with affected males transmitting the gene to all daughters and none of their sons?

Duchenne Muscular Dystrophy

In X-Linked Dominant inheritance, how are X-linked phenotypes described?

Regularly expressed in heterozygotes

Which disorder is characterized by the absence of pigment in the skin, hair, and eyes?

Albinism

Royal Hemophilia is associated with which type of inheritance?

What is the type of inheritance observed in Turner syndrome?

In X-Linked Recessive inheritance, what is the chance for isolated cases to be new mutations?

Study Notes

Autosomal Recessive: 1/4 of the offspring of two heterozygous carriers will be affected, consanguinity is more common, affected parents are unaffected gene carriers, unaffected siblings have a 2/3 chance to be carriers, children of affected individuals are obligate carriers.
Autosomal Recessive Disorders: Congenital Deafness, Diabetes Mellitus, Sickle Cell anemia, Albinism, Phenylketoneuria, Galactosemia, Cystic Fibrosis, Tay Sachs Disease.
X-Linked Inheritance: Affected males are hemizygous, affected females are homozygous, affected males transmit the gene to all daughters, females have two cell populations, Duchenne muscular dystrophy shows typical mosaic expression in females.
X-Linked Recessive: Males are more often affected than females, affected males pass the gene to all daughters and none of their sons, daughters of carrier females have a 50% chance to be unaffected carriers, affected males are related through carrier females.
X-Linked Recessive: 1/3 of isolated cases are new mutations, in 2/3 of cases the mother is an unaffected carrier, female gene carriers are usually not affected, exceptions include Turner syndrome, skewed X-inactivation, X;autosome translocation carriers.
X-Linked Dominant Inheritance: X-linked phenotypes can be described as dominant if they are regularly expressed in heterozygotes, females have a pair of X chromosomes, each child of an affected female has a 50% chance of inheriting the trait, regardless of sex.
Hemophilia A: X-linked recessive disorder, blood fails to clot normally due to a deficiency of factor VIII.
Royal Hemophilia: X-linked dominant inheritance, all daughters and none of the sons of affected males are affected, females have the same pattern of inheritance as autosomal dominant inheritance.

Test your knowledge on autosomal recessive inheritance and the conditions determined by the altered gene. Understand the concept of homozygote and heterozygote individuals and their parental carriers.

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