Medical Genetics: The Basics Trivia Quiz

Answer: When a couple is identified as at risk for developing a genetic disease.

Prospective genetic counseling is anticipatory in that an individual or couple is identified as being at increased risk for developing a genetic disease or birth defect or of having a child with a similar problem before its occurrence. Candidates for prospective genetic counseling include couples in which either the father or mother is older or in which one member of the couple is at risk for having a particular genetic disease that is more prevalent in their ethnic or racial group (cystic fibrosis, sickle cell anemia, Tay-Sachs disease, beta or alpha thalassemia). Retrospective counseling is given after an individual develops a genetic disorder or after a couple has a child with a particular birth defect or genetic disease. Until recently, most genetic counseling was retrospective. Currently, more at-risk situations can be identified before conception, and the individual or couple can be given prospective counseling.

Answer: A woman with 45 chromosomes, with a Robertsonian translocation between chromosomes 14 and 21.

The woman with 45 chromosomes and Robertsonian translocation between chromosomes 14 and 21 will be normal, but her offspring are at risk of developing Down's syndrome if she passes the translocated chromosome. The woman with 46 chromosomes will have trisomy for chromosomes 14 or 21.

The woman with a karyotype 47,XX,+18 will have trisomy for chromosome 18. The man will be deficient for the genes located on the deleted material.

Answer: It is characterised by a 47,XXY karyotype with hypogonadism after puberty.

Individuals with Klinefelter's syndrome usually appear normal with only tall stature until puberty at which time secondary sexual characteristics fail to develop, and hypogonadism appears. The genitalia are not ambiguous. There is no evidence that individuals with this syndrome are more prone to criminality than the general male population.

Answer: They almost always display short stature.

Short stature is a universal feature of women with Turner's syndrome. They are at increased risk of developing autoimmune thyroiditis, but they are not at an increased risk for breast cancer. They usually do not undergo complete development of their secondary sexual characteristics. They are not mentally retarded, but they may experience certain learning disabilities.

Answer: A derivative chromosome formed by a translocation between chromosomes 9 and 22.

A translocation between chromosomes 9 and 22 yields a small derivative chromosome referred to as the Philadelphia (Ph) chromosome, which is most commonly associated with chronic myelogenous leukemia (although it is seen in acute form). There is no association between the Ph chromosome and spontaneous abortions.

Answer: It is caused by mutations or deletion of both copies of the RB1 gene.

The retinoblastoma gene is is a tumor-suppressor gene; therefore, for development of a tumor, both copies must be inactivated by either mutations or deletions. Osteosarcoma is often seen as a secondary tumor in familial retinoblastoma patients, but this usually occurs later in life.

Answer: Mutations in a mitochondrial transfer RNA gene, resulting in defects in multiple mitochondrial protein complexes.

Both MERRF and MELAS are caused by mutations in transfer RNA (tRNA) genes. MERRF is caused by a mutation in the gene for tRNA-lysine, and MELAS is caused by a mutation in the gene for tRNA-leucine. Other known mitochondrial diseases are Leber's hereditary optic neuropathy, Kearns-Sayre syndrome and a form of deafness which can be caused by a mutation in the 12S RNA gene.

Answer: It is a conception with one extra haploid set of chromosomes.

Triploidy is a conception with one extra haploid set of chromosomes, giving rise to a 69,XXX (XXY or XYY) chromosomal complement, whereas trisomy is a conception with only one extra chromosome. Most conceptions involving triploidy do not survive to term, and those that do survive usually die within several hours of birth.

It is the second most common cytogenetic abnormality seen in spontaneous abortions, accounting for approximately 16% of chromosomally abnormal cases.

Answer: The father is a carrier of a 14;21 translocation.

CVS is conducted in the first trimester of pregnancy due to the fact that chorionic villi are loose in that time, therefore they can be easily aspirated. Due to the fact that the villi have the same origin as the fetus, assessment of the chromosomal or biochemical status of the villi provides information identical to the information obtained by amniocentesis.

A father carrying a 14;21 translocation has a 3% chance of having a child with Down's syndrome. A pregnancy at risk for neural tube defect is evaluated by measurement of the level of alpha-fetoprotein, which is a substance present only in amniotic fluid and maternal serum, not in chorionic villi. CVS would not be indicated as a method for chromosome studies as late as 20 weeks gestation.

A family member with Down's syndrome is not an indication for prenatal diagnosis in general, unless the individual has a translocation form of Down's syndrome. Prior to offering diagnostic testing, blood chromosomes should be done on the patient to determine if he/she is a carrier of a translocation, if the chromosomes of the brother are not known.

Answer: Gene dosage compensation in mammals.

X chromosome inactivation is seen in any individual with 2 or more X chromosomes and is responsible for maintaining dosage compensation for genes on the X chromosome.