Question 1

Which chromosomal abnormality is most likely to result in a gene dosage imbalance and is usually more harmful than changes in ploidy?

Accepted Answer

Aneuploidy

Question 2

A patient is found to have 47 chromosomes due to an extra copy of chromosome 21. Which term best describes this condition, and what is the equation for the chromosome number?

Accepted Answer

Trisomy; $$2n + 1 = 47$$

Question 3

Which chromosomal structural change provides raw material for evolution by allowing one gene copy to accumulate mutations and potentially acquire a new function?

Accepted Answer

Duplication

Question 4

A carrier of a Robertsonian translocation involving chromosomes 14 and 21 has 45 chromosomes. Which outcome is possible for their offspring?

Accepted Answer

Some offspring may have translocation Down syndrome

Question 5

Which mechanism is most commonly responsible for the formation of mosaicism in an individual?

Accepted Answer

Nondisjunction in mitosis early in development

Question 6

In a paracentric inversion heterozygote, what is the result of a crossover within the inversion loop during meiosis?

Accepted Answer

Two viable parental gametes and two inviable recombinant products

Question 7

A child inherits a mitochondrial disorder from their mother, but the severity differs among siblings. Which concept best explains this variation?

Accepted Answer

Heteroplasmy and replicative segregation

Question 8

Which of the following is NOT evidence supporting the endosymbiotic theory for the origin of mitochondria and chloroplasts?

Accepted Answer

Presence of 80S ribosomes

Question 9

A plant with variegated leaves is crossed as the egg parent with a green pollen donor. What types of offspring are expected?

Accepted Answer

Green, white, and variegated

Question 10

Which ribosome type is found in mammalian mitochondria, and what are its subunits?

Accepted Answer

55S; 28S and 39S

Question 11

A patient with phenylketonuria (PKU) has a deficiency in which enzyme, and what is the biochemical consequence?

Accepted Answer

Phenylalanine hydroxylase; accumulation of phenylpyruvate and phenylacetate

Question 12

Which genetic test is best suited to detect a known point mutation that alters a restriction site, such as the sickle cell mutation?

Accepted Answer

RFLP (restriction fragment length polymorphism)

Question 13

A newborn is screened for sickle cell disease using hemoglobin electrophoresis. Which mutation is responsible for sickle cell disease?

Accepted Answer

A point mutation changing GAG to GTG in codon 6 of HBB

Question 14

Which equation represents the number of chromosomes in a human with tetrasomy for the X chromosome?

Accepted Answer

$$2n + 2 = 48$$

Question 15

A patient with alkaptonuria (AKU) presents with darkening urine and ochronosis. Which metabolic pathway is disrupted, and which compound accumulates?

Accepted Answer

Tyrosine/phenylalanine degradation; homogentisic acid

Question 16

Which feature distinguishes a pericentric inversion from a paracentric inversion?

Accepted Answer

The centromere is inside the inverted segment in pericentric inversion

Question 17

Which concept explains why symptoms of mitochondrial diseases appear only when the proportion of mutant mtDNA exceeds a certain level?

Accepted Answer

Threshold effect

Question 18

A disease appears earlier and more severely in successive generations due to expansion of a trinucleotide repeat. Which term describes this phenomenon?

Accepted Answer

Genetic anticipation

Question 19

Which equation describes the outcome of meiosis I nondisjunction in humans?

Accepted Answer

2 n+1 gametes, 2 n-1 gametes, 0 normal

Question 20

Which of the following best describes the modern view of the 'one gene-one enzyme' theory?

Accepted Answer

One gene can encode one or more products, including polypeptides and functional RNAs

Chromosome Abnormalities, Extranuclear Inheritance, and Biochemical Genetics: Study Guide

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