CSIR Life science - Cell Biology Model Questions Part - 6

51. If a fragment of a chromosome breaks off and then reattaches to the original chromosome but in the reverse direction, the resulting chromosomal abnormality is called
(a) a deletion. (b) an inversion.
(c) a translocation. (d) a nondisjunction.

52. Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?
(a) There are probably more genes on chromosome 21 than on the others.
(b) Chromosome 21 is a sex chromosome and 3 and 16 are not.
(c) Down syndrome is not more common, just more serious.
(d) Extra copies of the other chromosomes are probably fatal.

53. Humans have 23 pairs of chromosomes, while our closest relatives, chimpanzees, have 24. Chromosome studies indicate that at some point early in human evolution, two chromosomes simultaneously broke into a large portion and a small portion. The large parts combined to form a large chromosome, and the small parts combined to form a much smaller chromosome (which was subsequently lost). This important chromosomal change could best be described as
(a) nondisjunction followed by deletion.
(b) translocation followed by deletion.
(c) duplication followed by deletion.
(d) translocation followed by inversion.

54. Each cell in an individual with Down syndrome contains ____ chromosomes.
(a) 3 (b) 22
(c) 24 (d) 47

55. Disorders involving unusual numbers of sex chromosomes show that maleness is caused by the
(a) presence of an X chromosome.
(b) presence of a Y chromosome.
(c) absence of an X chromosome.
(d) absence of a Y chromosome.

56. A particular allele can have different effects if it was inherited from a male rather than a female. This phenomenon is known as
(a) extranuclear inheritance. (b) aneuploidy.
(c) sex-linkage. (d) genome imprinting.

57. Human mitochondria
(a) are inherited as an X-linked trait.
(b) are all inherited from the father.
(c) have linear DNA.
(d) are all inherited from the mother.

58. Both chloroplasts and mitochondria
(a) are found within the nucleus.
(b) have linear DNA.
(c) carry extranuclear genes.
(d) are inherited from both parents.

59. Damaged DNA is excised by
(a) restriction enzymes. (b) helicase.
(c) primase. (d) DNA polymerase.

60. Unlike prokaryotic DNA replication, eukaryotic DNA replication
(a) is completed by DNA polymerase.
(b) cannot be completed by DNA polymerase.
(c) is semiconservative.
(d) has a multiple origin.

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