Inheritance and Genetics MCQs for MDCAT

Correct answer: C. Telophase

Telophase is the mitotic stage in which chromosomes uncoil, nucleoli reform, and two separate nuclei form at opposite poles of the cell.

Correct answer: B. Down's Syndrome

Maternal non-disjunction of an autosomal pair, producing an egg with 24 chromosomes, is the usual origin of Down's syndrome.

Correct answer: B. Severe Combined Immunodeficiency Syndrome (SCID)

In gene therapy for Severe Combined Immunodeficiency Syndrome (SCID), genetically engineered cells carrying a functional ADA gene are introduced into the patient's bone marrow.

Correct answer: B. Microinjection

Microinjection is the technique used in transgenic animals in which the desired gene is directly injected into a fertilized egg using a fine needle.

Correct answer: C. Epistasis

Epistasis occurs when the presence of a particular gene at one locus suppresses or masks the phenotypic effect of a gene at another locus.

Correct answer: A. Epistasis

Epistasis is the phenomenon in which a gene at one locus masks or expresses over the effect of a gene at another locus.

Correct answer: B. Human blood group

Human blood group (ABO system) is a trait determined by three different alleles (IA, IB and i) at a single locus, illustrating multiple allelism.

Correct answer: C. Locus

Locus is the physical position a gene or a factor occupies on the chromosome.

Correct answer: D. Ontogeny recapitulates phylogeny

This concept, proposed by Ernst Haeckel, suggests that the development of an individual organism (ontogeny) follows the same sequence of evolutionary changes seen in the evolutionary history of the species (phylogeny). According to this idea, an organism goes through stages during its development that resemble the adult forms of its evolutionary ancestors.

Correct answer: C. Pedigree analysis

Pedigree analysis is the most commonly used method to trace the mode of inheritance in humans. It involves the construction of a family tree or pedigree that tracks the occurrence of a trait through generations.

Correct answer: C. Crossing over

Crossing over produces new allele combinations during meiosis, greatly enhancing variation. Asexual methods do not increase variation.

Correct answer: A. Prophase meiosis I

Option A is correct. Crossing over occurs during prophase I of meiosis I, when homologous chromosomes pair up and exchange segments of their genetic material, leading to genetic variation in the offspring. In contrast, Option B is incorrect because prophase II occurs after the homologous chromosomes have been separated, and no crossing over takes place. Option C is also incorrect; during metaphase I, homologous chromosomes align but do not exchange genetic material. Lastly, Option D is incorrect as anaphase II focuses solely on the separation of sister chromatids, with no involvement of crossing over.