Tay-Sachs Disease Genetics Quiz

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Questions and Answers

What is the primary cause of Tay-Sachs disease?

Sphingomyelinase deficiency

GM1 ganglioside accumulation

Beta-hexosaminidase A deficiency (correct)

Beta-glucosidase A deficiency

In a scenario where the mother has the mutation p.Arg170Gln and the father has p.Tyr427fs, what is the expected inheritance pattern in their offspring?

All daughters will be affected

None of the offspring can be carriers

1 in 4 offspring will be affected (correct)

All sons will be carriers

Which statement about X-linked recessive disorders is correct?

All sons of affected males are affected

Affected females are asymptomatic

Daughters of affected males will all be carriers (correct)

Carrier females cannot have affected offspring

What characterizes the mutation p.Tyr427fs associated with Tay-Sachs disease?

It causes a non-functional beta-hexosaminidase A enzyme Signup and view all the answers

How does X-linked inheritance typically affect males related via the female line?

They are typically symptomatic and affected Signup and view all the answers

What is a possible reason that females can be affected by an X-linked recessive disorder?

They have random X chromosome inactivation leading to expression in some tissues Signup and view all the answers

What type of inheritance pattern is exhibited by Myotonic Dystrophy?

Autosomal dominant Signup and view all the answers

Which of the following correctly describes the risk of an affected parent transmitting an autosomal dominant condition?

There is a 50% chance of transmission Signup and view all the answers

Which characteristic is NOT associated with autosomal dominant conditions?

Maternal inheritance only Signup and view all the answers

What does reduced penetrance refer to in the context of autosomal dominant conditions?

Not all carriers exhibit symptoms Signup and view all the answers

In autosomal dominant inheritance, what is a key feature observed?

Vertical inheritance pattern Signup and view all the answers

Which statement best represents variable expression in autosomal dominant conditions?

Expression of the condition can vary among individuals Signup and view all the answers

What is a primary purpose of genetic testing in the context of genetic disorders?

For diagnosis and confirmation of genetic disorders Signup and view all the answers

Which of the following is NOT a benefit of genetic diagnosis?

Guarantees a definitive cure for all disorders Signup and view all the answers

What key information is essential for accurate risk assessment in genetic counseling?

Confirmation of the diagnosis, family tree, and inheritance pattern Signup and view all the answers

In autosomal dominant inheritance, what is the recurrence risk to offspring from a parent with the genotype Aa?

50% chance of inheriting the dominant trait Signup and view all the answers

What does pre-implantation genetic diagnosis (PGD) facilitate?

Selection of embryos without genetic disorders Signup and view all the answers

Which condition could be confirmed through genetic testing as the only diagnostic test in some cases?

Duchenne muscular dystrophy Signup and view all the answers

What is one of the roles of genetic testing regarding family members?

To test for carrier or pre-symptomatic conditions in at-risk relatives Signup and view all the answers

Which aspect is commonly assessed to provide informed choices in future pregnancies?

Accurate familial risk estimations and management options Signup and view all the answers

What is the probability that child II.1 will inherit allele A or a from I.1?

0.5 Signup and view all the answers

What is the risk of having a child affected by retinoblastoma if the parent is a heterozygote?

0.4 Signup and view all the answers

In X-linked inheritance, what is the probability of a carrier female having an affected child?

1/8 Signup and view all the answers

What does incomplete penetrance imply in the context of retinoblastoma?

A fraction of heterozygotes will develop the disease. Signup and view all the answers

For autosomal recessive inheritance, what is the likelihood that an unaffected sibling is a carrier?

2/3 Signup and view all the answers

What characterizes variable expression in Neurofibromatosis type I?

Diverse phenotypic manifestations. Signup and view all the answers

How is the probability of a child inheriting cystic fibrosis from carrier parents determined?

1/4 due to the genetic combinations of the parents. Signup and view all the answers

What is the ratio of affected to unaffected offspring in X-linked inheritance, provided a carrier female?

1:1 for affected and unaffected. Signup and view all the answers

What is the relationship between the incidence of cystic fibrosis and the estimated carrier frequency?

Carrier frequency approximates to 2q when incidence is low. Signup and view all the answers

If the incidence of cystic fibrosis is 1 in 2500, what is the approximated carrier frequency?

1/25 Signup and view all the answers

Why is it essential to establish a genetic diagnosis?

To facilitate management and treatment options. Signup and view all the answers

What is the offspring risk calculation when both parents are considered carriers?

1/150 Signup and view all the answers

In the context of cystic fibrosis, what does q represent in the Hardy-Weinberg principle?

The recessive allele frequency in the population. Signup and view all the answers

How does the Hardy-Weinberg principle assist in risk calculation?

It estimates frequencies of alleles and genotypes in a population. Signup and view all the answers

What is one potential benefit of genetic diagnosis beyond establishing a clinical diagnosis?

It might predict the necessity for gene-based therapies. Signup and view all the answers

What explains the approximate value of the carrier frequency being 2pq?

With p being close to 1, 2pq simplifies to approximately 2q. Signup and view all the answers

Study Notes

Inheritance Patterns

Myotonic Dystrophy follows an autosomal dominant inheritance pattern, featuring anticipation.
Autosomal dominant conditions arise from mutations in a single autosomal gene, usually resulting in affected individuals being heterozygous.
Each affected individual has a 50% chance of passing the condition to offspring, with male-to-male transmission being a key feature.

Characteristics of Autosomal Dominant Disorders

Vertical inheritance ensures transmission across generations.
Males and females are affected equally, with affected parents capable of transmitting the disorder to both sons and daughters.
Key characteristics include reduced penetrance and variable expression.

Reduced Penetrance

Refers to the proportion of individuals with a mutation who exhibit phenotypic symptoms, meaning not all mutation carriers show symptoms.
Example: In Tay-Sachs disease, mutations in the HEXA gene lead to variable expression of symptoms.

X-Linked Inheritance

In X-linked recessive disorders, typically only males related through the female line are affected.
Carrier females have a 50% chance of passing the disorder to each son, while all daughters of an affected male become carriers.

Genetic Diagnosis and Testing

Single gene testing assists in diagnosing genetic disorders, managing them, and estimating recurrence risks for families.
Prenatal (PND) and pre-implantation genetic diagnosis (PGD) offer reproductive options for at-risk families.
Accurate genetic diagnosis often limits other diagnostic procedures and provides information for future pregnancies.

Cystic Fibrosis Examples

In a population with a cystic fibrosis incidence of 1 in 2500, carrier frequency approximates to 1 in 25.
Risk assessment shows that if both parents are carriers with no family history, the chance of having an affected child is 1 in 150.

Key Concepts in Risk Assessment

Risk figures for adult-onset genetic conditions help inform family members regarding the likelihood of inherited disorders.
Genetic testing refines risk assessments and helps in creating informed choices concerning future pregnancies.

In conditions like retinoblastoma, incomplete penetrance can lead to sporadic cases, with only a portion of carriers developing symptoms.
Variable expression in conditions such as neurofibromatosis type I demonstrates the diversity of phenotypic traits among affected individuals.

Overview of Hardy-Weinberg Principle

The Hardy-Weinberg principle aids in understanding carrier frequencies and genetic equilibrium in populations.
Calculating incidences and carrier frequencies assists in genetic counseling and understanding autosomal recessive inheritance patterns.

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Description

This quiz dives into the genetic factors associated with Tay-Sachs disease, including the inheritance patterns, specific mutations like p.Arg170Gln and p.Tyr427fs, and the characteristics of X-linked recessive disorders. Test your understanding of these complex genetic topics and their implications on offspring inheritance.