17 Questions
In autosomal recessive inheritance, how many copies of an altered gene must be present for an individual to be affected?
Two copies
What is the risk for males and females to be affected in autosomal recessive inheritance?
Equal risk for both males and females
What is the typical outcome when 2 affected individuals in autosomal recessive inheritance produce children?
All children are affected
What is the expected ratio of normal homozygotes, carrier heterozygotes, and affected individuals in the offspring of parents who are carriers for autosomal recessive genes?
1:2:1
Which of the following is true about X-linked dominant disorders?
Females are about 2x as likely to be affected than males in rare conditions.
What is a characteristic feature of Y-linked (Holandric) disorders?
Affected males pass the disease gene to all their sons and to none of their daughters.
What is true about the expression of X-linked dominant disorders in females?
They are usually milder, but variable, in females because the mutant allele is located on the inactive X chromosome in a proportion of their cells.
Which statement is true regarding male-to-male transmission in X-linked disorders?
Most X-linked conditions are typically apparent only in females.
In X-linked inheritance, which of the following is true about affected males?
They transmit the gene to all daughters but not to any sons.
Which of the following is a characteristic of X-linked recessive disorders?
1/3 of isolated cases are due to a new mutation.
What distinguishes X-linked dominant inheritance from autosomal dominant inheritance?
Lack of male-to-male transmission
Which statement is true regarding the expression of X-linked recessive disorders in females?
X inactivation leads to females having two cell populations expressing alleles on both X chromosomes.
What is the recurrence risk for affected parents in autosomal recessive inheritance?
1 in 4 or 25%
What is true about X-linked recessive disorders?
Daughters of carrier females have a 25% chance to be unaffected carriers.
Which statement is true regarding consanguinity and autosomal recessive disorders?
Consanguinity may make autosomal recessive conditions seem recessive rather than dominant.
What is a distinguishing feature of X-linked recessive disorders compared to X-linked dominant disorders?
Male-to-male transmission
What is an example of an X-linked dominant disorder according to the given text?
Hemophilia A
Study Notes
- Autosomal Recessive Disorders: 1/4 of the offspring of two heterozygous carriers are affected. parents of an affected child are unaffected gene carriers. Recurrence risk for affected parents is 1 in 4 or 25%. Unaffected siblings have a 2/3 or 67% chance of being carriers. Children of affected individuals are obligate carriers. Consanguinity is more common in pedigrees involving AR and may make condition seem dominant. Some examples of AR disorders include congenital deafness, diabetes mellitus, sickle cell anemia, albinism, and phenylketoneuria.
- X-Linked Inheritance: X-linked inheritance mainly affects males. Affected males are hemizygous, and affected females are homozygous. Affected males transmit the gene to all daughters but not to any sons. X inactivation, a normal physiological process, leads to females having two cell populations, which express alleles of X-linked genes on one or the other of the two X chromosomes. X-linked recessive disorders are generally restricted to males. Affected males pass the gene to all of their daughters and none of their sons. Daughters of carrier females have a 50% chance to be unaffected carriers.
- X-Linked Recessive Disorders: An X-linked recessive mutation is expressed in all males who receive it. X-linked recessive disorders are generally restricted to males. Affected males pass the gene to all of their daughters and none of their sons. Daughters of carrier females have a 50% chance to be unaffected carriers. Affected males in the family are related to each other through carrier females. X-linked recessive disorders include Duchenne muscular dystrophy, hemophilia A, and some other disorders.
- X-Linked Dominant Inheritance: X-linked dominant inheritance affects both males and females. All daughters and none of the sons of affected males are affected. X-linked dominant inheritance is distinguished from autosomal dominant inheritance by the lack of male-to-male transmission. Hemophilia A, a classic X-linked recessive disorder, is an example of an X-linked dominant condition.
- X-Linked Recessive Disorders Characteristics: X-linked recessive disorders have specific characteristics. 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, but there are exceptions like Turner syndrome, skewed X-inactivation, and X;autosome translocation carriers. X-linked recessive disorders have a distinctive inheritance pattern.
- X-Linked Recessive Disorders: X-linked recessive disorders have certain patterns. Affected males pass the gene to all of their daughters and none of their sons. Daughters of carrier females have a 50% chance to be unaffected carriers. Affected males in the family are related to each other through carrier females. 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. X-linked recessive disorders are not limited to any specific disorder and can affect various aspects of health.
- X-Linked Recessive Disorders: X-linked recessive disorders can be found in various aspects of health. Hemophilia A, a classic X-linked recessive disorder, is a disorder that affects the blood's ability to clot normally. Hemophilia A is characterized by a deficiency of factor VIII, a protein in the clotting cascade. Affected males have a hemorrhagic diathesis, resulting in prolonged bleeding from wounds and easy bruising. X-linked recessive disorders are not limited to Hemophilia A and can affect various other aspects of health.
Test your knowledge on autosomal recessive inheritance, where an individual must inherit two copies of an altered gene to be affected. This quiz covers the basics of how this mode of inheritance works and its implications for individuals and their families.
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