Unit 3: Chromosomal Variations and Mutations - Practice Quiz

1 A chromosomal aberration in which a segment of a chromosome is lost is called a:

2 When a segment of a chromosome is present in two copies within the same chromosome, the aberration is called a:

3 In which chromosomal aberration is a segment reversed end to end within the same chromosome?

4 The transfer of a chromosome segment to a non-homologous chromosome is known as:

5 The failure of chromosomes to separate properly during cell division is called:

6 A condition in which the chromosome number differs from the normal by one or a few chromosomes is called:

7 Down syndrome is caused by an extra copy of which chromosome?

8 Trisomy 18 is also known as:

9 Patau syndrome results from an extra copy of which chromosome?

10 Turner syndrome in humans has which sex chromosome constitution?

11 Klinefelter syndrome is characterized by which chromosome constitution?

12 The condition called superfemale (triple X syndrome) has which chromosome constitution?

13 Which sex-linked aneuploidy typically results in a phenotypic female who is often sterile and short in stature?

14 The condition of having more than two complete sets of chromosomes is called:

15 Polyploidy is most commonly observed in:

16 Compared to plants, polyploidy in animals is generally:

17 A mutation is best defined as a:

18 A mutation involving the change of a single base pair in DNA is called a:

19 A mutation that changes a codon into a stop codon, prematurely ending translation, is called a:

20 Which of the following is a physical mutagen that can induce mutations?

21 A chromosome with the gene order produces a mutant with the order . What structural change has occurred?

22 The Bar eye phenotype in Drosophila, which reduces eye facet number, is classically explained by which structural chromosomal change?

23 During meiosis in a heterozygote carrying a paracentric inversion, a single crossover within the inversion loop typically produces which abnormal products?

24 A phenotypically normal person carries a balanced reciprocal translocation. Why are they usually unaffected, yet at risk of having children with abnormalities?

25 If non-disjunction occurs during meiosis II in one secondary oocyte, what is the expected composition of the resulting gametes from that cell?

26 A newborn presents with a single palmar crease, upslanting palpebral fissures, hypotonia, and intellectual disability. Which trisomy is most consistent with these findings?

27 Trisomies 13 and 18 have far lower survival than trisomy 21 primarily because

28 A phenotypic female with short stature, webbed neck, and non-functional ovaries is found to have 45 chromosomes. Her karyotype is most likely

29 How many Barr bodies are present in the somatic cells of an individual with Klinefelter syndrome (47,XXY)?

30 A woman with a 47,XXX karyotype ("superfemale" / Triple X) is often only mildly affected because

31 An autotetraploid plant is produced by doubling the chromosome set of a diploid (). If the diploid has , how many chromosomes does the autotetraploid have?

32 Which agent is most commonly used experimentally to induce polyploidy in plants by preventing spindle fiber formation?

33 Allopolyploids differ from autopolyploids in that allopolyploids

34 Polyploidy is far rarer and usually lethal in animals compared with plants mainly because

35 Which statement best defines a mutation in the genetic sense?

36 Insertion of a single nucleotide within the coding region of a gene most likely causes which type of mutation?

37 A point mutation changes the codon (Tyr) to (stop). This is best classified as a

38 Sickle-cell anemia results from a single base substitution changing glutamic acid to valine in -globin. This is an example of a mutation whose phenotypic effect is

39 The base analog 5-bromouracil (5-BU) induces mutations because it

40 Ultraviolet (UV) light is a mutagen that primarily damages DNA by

41 A pericentric inversion heterozygote forms an inversion loop during meiosis I. If a single crossover occurs within the inversion loop, what is the expected outcome for the resulting recombinant gametes?

42 A phenotypically normal individual is a carrier of a balanced reciprocal translocation. During meiosis, the four chromosomes form a cross-shaped quadrivalent. Which segregation pattern yields genetically balanced gametes?

43 A woman with a Robertsonian translocation between chromosomes 14 and 21 [karyotype 45,XX,der(14;21)] is having children. Ignoring lethality and gametes lacking chromosome 21, what is the theoretical risk that a liveborn child has translocation Down syndrome, based on the balanced gamete types?

44 A trisomic (2n+1) plant heterozygous for the extra chromosome (genotype ) is testcrossed to . Assuming the extra chromosome segregates as random chromosome pairs (only balanced gametes function equally) and considering only chromosome segregation, what fraction of the diploid () offspring will express the recessive phenotype?

45 A patient has the karyotype 47,XXY. According to the Lyon hypothesis, how many Barr bodies are expected, and why does the individual still show a phenotype despite X-inactivation?

46 A point mutation changes the DNA triplet from to on the template strand. This substitution involves a purine replaced by a purine (). How is this mutation best classified at the molecular level?

47 The chemical mutagen 5-bromouracil (5-BU) induces mutations primarily because:

48 An allotetraploid was formed by chromosome doubling of a sterile hybrid between species A () and species B (). What is the somatic chromosome number of the fertile allotetraploid?

49 A single base insertion occurs near the 5' end of a coding sequence, but a compensating single base deletion occurs a few codons downstream. What is the most likely consequence?

50 In a Drosophila mapping experiment, a recessive allele becomes phenotypically expressed in a heterozygote that carries a chromosomal deletion on the homolog. What does this phenomenon reveal?

51 The Bar eye phenotype in Drosophila results from a tandem duplication that can undergo unequal crossing over. When two Bar chromosomes pair and unequal crossing over occurs, one product is Double-Bar and the other is:

52 Patau syndrome (trisomy 13) and Edwards syndrome (trisomy 18) can both arise from meiotic non-disjunction. Which statement best distinguishes the cytogenetic origin contributing to advanced maternal age effects in these autosomal trisomies?

53 Polyploidy is far rarer and usually less tolerated in animals than in plants. Which explanation is the primary reason?

54 A missense mutation replaces a buried hydrophobic valine with a charged glutamate deep in a protein's core, whereas the same amino-acid change on the surface has little effect. This illustrates that the phenotypic severity of a missense mutation depends most on:

55 A DNA sequence contains the run . During replication, strand slippage in such a short tandem repeat most commonly produces:

56 A 45,X (Turner) individual and a 47,XXX (triple-X/superfemale) individual differ strikingly in phenotypic severity, with Turner being far more clinically significant. The best explanation is:

57 Why do paracentric inversion heterozygotes appear as "crossover suppressors" in genetic mapping, even though crossing over still physically occurs within the loop?

58 A child has the karyotype 47,XY,+21 but the parents are chromosomally normal. DNA polymorphism analysis shows the child inherited two different maternal alleles (both maternal homologs) at centromeric loci of chromosome 21. This indicates the non-disjunction occurred at:

59 Autopolyploids often show reduced fertility compared to their diploid progenitors. In an autotetraploid, the primary cytological cause of this reduced fertility is:

60 Ionizing radiation (e.g., X-rays) and ultraviolet (UV) light both damage DNA but by different primary mechanisms. Which pairing correctly matches the agent to its characteristic lesion?