Practice Exam-Developmental Genetics

Developmental Genetics

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The provided document contains two practice exam questions on developmental genetics, followed by commentary and references explaining the correct answers.<br /><br />**Question 25227** deals with a nasal sample from a patient suspected of having a ciliary function issue. The results show abnormalities in the dynein arms of the cilia. The multiple-choice question asks which diagnosis is consistent with these findings. The commentary clarifies that Bardet-Biedl syndrome, Grieg cephalopolysyndactyly syndrome, Holoprosencephaly, and Joubert syndrome are related to signal transduction defects in cilia but do not involve structural defects. Situs inversus, however, is often linked to mutations in ciliary dyneins, observable as structural defects in the dynein arms via electron microscopy. Thus, the answer is **E. Situs inversus**.<br /><br />**Question 25226** presents two clinical cases: a 4-year-old boy and an unrelated 6-month-old girl, both with anemia. The boy's genetic analysis shows compound heterozygosity with deletions in the alpha-globin gene, while the girl's genetic analysis identifies a homozygous stop codon mutation in the beta-globin gene. The question asks which genetic concept explains these findings. Commentary provides definitions of several genetic principles: locus heterogeneity, allelic heterogeneity, incomplete penetrance, pleiotropy, and variable expressivity. The correct explanation involves locus heterogeneity, where mutations at different genetic loci result in similar phenotypes. Thus, the answer is **C. Locus heterogeneity**.<br /><br />These summaries assist in understanding the genetic diagnosis processes and principles through practical application in clinical scenarios.

Keywords

developmental genetics

ciliary function

dynein arms

situs inversus

locus heterogeneity

genetic diagnosis

alpha-globin gene

beta-globin gene

clinical scenarios

genetic principles