Biology

Human Genetics and Disorders

882 Questions

Human Genetics and Disorders covers the inheritance patterns, genetic mutations, and molecular basis of hereditary diseases. Topics include sex-linked traits, cancer genetics, and metabolic disorders. This section tests knowledge critical for biology exams and general science papers.

Genetic mutationsInherited disordersCancer geneticsGenetic testingMendelian inheritance

Human Genetics and Disorders Questions

Multiple choice

A 30 year girl individual whose father has Huntington disease requests genetic testing to determine if she has inherited the mutation. She is so far asymptomatic. What should he counselled?

  1. At 30 years of age, she would already have shown symptoms if she had inherited the mutation.

  2. She faces a 50-50 risk of developing symptoms of Huntington disease.

  3. She remains at risk at age 30, though his risk is less than 50% being asymptomatic at this age.

  4. The fact that her father was the affected parent indicates that she must not have inherited the gene, since paternally-transmitted Huntington disease has onset in childhood.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Huntington disease displays age-dependent penetrance. So, her risk is now less than 50% though it is still possible that she will develop the disorder.

Multiple choice

Mutation in the RET oncogene is associated with increased risk of

  1. colon cancer

  2. endometrial cancer

  3. medullary thyroid cancer

  4. prostate cancer
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

RET mutation is responsible for increased risk of medullary thyroid cancer as well as multiple endocrine neoplasia 2, in which pheochromocytoma and parathyroid adenoma also occur.

Multiple choice

Homozygosity for a mutation that leads to decreased activity of thiopurine methyltransferase is associated with

  1. increased activity of 6-mercaptopurine

  2. decreased activity of 6-mercaptopurine

  3. increased rate of excretion of 6-mercaptopurine

  4. decreased rate of excretion of 6-mercaptopurine
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Decreased activity of TMPT leads to increased levels of active 6-mercaptopurine, since the drug is normally inactivated by the enzyme. This is associated with toxicity of the chemotherapeutic drug.

Multiple choice

Amsterdam criteria is used in risk assessment of

  1. hereditary nonpolyposis colon cancer

  2. familial adenomatous polyposis

  3. hereditary breast and ovarian cancer

  4. cowden syndrome
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The amsterdam criteria is used to assess risk of HNPCC or hereditary nonpolyposis colon cancer to guide identification of individuals for whom genetic testing may be helpful.

Multiple choice

The result of a predispositional test is most likely to be in the form of

  1. a 'yes' or 'no' answer to the question of whether an individual will develop disease

  2. a risk limited by recombination between a marker locus and a disease locus

  3. a risk figure based on rate of penetrance

  4. a relative risk figure
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Predispositional tests usually result in relative risk estimates.

Multiple choice

Microsatellite instability concerns with

  1. Hereditary nonpolyposis colon cancer

  2. Familial adenomatous polyposis

  3. Neurofibromatosis

  4. Hereditary breast cancer
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Microsatellite instability results from aberrant mismatch repair and is characteristic of HNPCC or Hereditary nonpolyposis colon cancer.

Multiple choice

Which among the following is a non-inherited genetic syndrome?

  1. Down syndrome

  2. Turner syndrome

  3. Deletion syndrome

  4. Williams syndrome
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Down syndrome is also called Trisomy 21. It is one of the most common, non-inherited genetic syndrome. It occurs in about 1 of every 200 to 250 births. In Down syndrome, a mistake in how the chromosomes segregate causes a child to inherit an extra chromosome 21.

Multiple choice

A couple decided to have an offspring and went to the genetic counselor. The lady told that her younger sister died in childhood with Down syndrome. There is no other family history of the condition. What is the most appropriate counseling?

  1. Down syndrome is generally random, so there is no increased risk to this couple.

  2. If results of the woman's sister's karyotype cannot be found, the woman herself should have chromosomal analysis.

  3. The pregnancy will be screened in the second trimester using alphafetoprotein, bhCG, and unconjugated estriol, which should be sufficient to detect Down syndrome if it has occurred.

  4. Prenatal diagnosis should be done by chorionic villus sampling or amniocentesis.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Although it is most likely that the sister with Down syndrome had trisomy 21, it is possible that she had a translocation and the woman herself could be a carrier. This could be resolved either by obtaining a report of the sister's karyotype, or performing chromosomal analysis on this woman.

Multiple choice

A 5 year old boy is found to have the karyotype 47, XXY. After being counseled about his diagnosis, his parents ask if he is at risk of passing this on to his son. What would you counsel them?

  1. There is a 50% risk that he will have a son with an extra X chromosome.

  2. He will be infertile so there is no risk of transmission.

  3. There is a slight possibility of fertility, and therefore he could have a chromosomally abnormal offspring.

  4. He will be unlikely to survive to reproductive age.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Most males with Klinefelter syndrome are infertile, although fertility is possible. He should be counseled about this possibility and the chance of having a chromosomally abnormal offspring, although the likelihood is low.

Multiple choice

A 3 year old girl with developmental delay is seen for evaluation. He has microcephaly, and his parents note that his birth weight was low. There is no known family history of similar problems. As routine karyotype is normal. His parents ask if there are additional cytogenetic tests that can be offered. What would you counsel them?

  1. A normal karyotype rules out all detectable chromosomal abnormalities.

  2. The girl should have FISH analysis for all known microdeletions.

  3. The chromosome study should be repeated in another laboratory.

  4. Analysis for subtelomere deletion may detect an abnormality missed by convential chromosomal analysis.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Subtelomere analysis offers a possibility to detect an abnormality that was not seen by conventional cytogenetic analysis.

Multiple choice

Failure to generate Mullerian-inhibiting substance in a genetic male would lead in

  1. failure of formation of testes

  2. presence of a uterus

  3. breast development at puberty

  4. stoppage of virilization of phallus
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Mullerian-inhibiting substance prevents development of the Mullerian ducts into a uterus and fallopian tubes. Absence of the substance would lead to persistence of these structures in a male.