Q40. When two non-homologous chromosomes exchange segments with each other, the change is called?
(A) Reciprocal translocation
(B) Deletion
(C) Monosomy
(D) Inversion
Answer: (A) Reciprocal translocation
Explanation: A reciprocal translocation involves mutual exchange of chromosome segments, typically between non-homologous chromosomes. A balanced carrier may have no obvious symptoms but may produce unbalanced gametes. Certain translocations also contribute to cancers through abnormal gene regulation.
Q39. A cell containing three complete chromosome sets, rather than three copies of only one chromosome, is?
(A) Monosomic
(B) Trisomic
(C) Triploid
(D) Haploid
Answer: (C) Triploid
Explanation: Triploidy is a form of polyploidy with three complete chromosome sets, written 3n. It differs from trisomy, which adds only one chromosome to a diploid complement. Polyploidy is common in many cultivated plants but usually incompatible with normal human development.
Q38. Which sex-chromosome combination characteristically occurs in Klinefelter syndrome?
(A) 45,X
(B) 47,XXY
(C) 47,XYY
(D) 46,XX
Answer: (B) 47,XXY
Explanation: Klinefelter syndrome typically affects individuals with a 47,XXY karyotype. The extra X chromosome may contribute to reduced testosterone production, small testes and infertility. A classic XXY somatic cell has one Barr body, representing the inactivated extra X.
Q37. Which chromosomal constitution is typically associated with Turner syndrome?
(A) 47,XXY
(B) 47,XXX
(C) 45,X
(D) 47,XY,+21
Answer: (C) 45,X
Explanation: Turner syndrome commonly involves monosomy X, shown as 45,X. Affected individuals typically develop as females and may have short stature or ovarian insufficiency. Some cases involve mosaic or structural X-chromosome abnormalities rather than complete monosomy.
Q36. An additional copy of chromosome 21 is the hallmark of which syndrome?
(A) Turner syndrome
(B) Down syndrome
(C) Klinefelter syndrome
(D) Cri-du-chat syndrome
Answer: (B) Down syndrome
Explanation: Down syndrome most commonly results from trisomy 21, producing 47 chromosomes in most cells. The extra chromosome changes gene dosage and is associated with characteristic developmental differences and increased risk of certain health problems, including congenital heart conditions.
Q35. How many Barr bodies are usually present in a somatic cell with the karyotype 47,XXY?
(A) Zero
(B) One
(C) Two
(D) Three
Answer: (B) One
Explanation: The number of Barr bodies is generally the number of X chromosomes minus one. In the usual XXY karyotype of Klinefelter syndrome, one of the two X chromosomes becomes inactivated, producing a single Barr body in many somatic cells.
Q34. Which test directly examines the number and gross structure of chromosomes in a cell?
(A) Karyotyping
(B) Urine culture
(C) Blood glucose test
(D) Spirometry
Answer: (A) Karyotyping
Explanation: Karyotyping arranges chromosomes for microscopic examination, allowing detection of many numerical and large structural abnormalities. It can identify common presentations of Down, Turner and Klinefelter syndromes, although small gene mutations typically need more sensitive molecular tests.
Q33. Two unaffected carriers of an autosomal recessive condition have a child. What is the probability that the child is affected?
(A) 0%
(B) 25%
(C) 50%
(D) 75%
Answer: (B) 25%
Explanation: When two heterozygous carriers are crossed, Aa × Aa, the predicted genotypes are AA, Aa, Aa and aa. Only aa is affected in a simple fully penetrant autosomal recessive disorder. Each pregnancy therefore has an independent one-in-four affected-child risk.
Q32. For a fully penetrant autosomal dominant disorder, an affected heterozygous parent (Aa) and an unaffected parent (aa) have what probability of an affected child?
(A) 0%
(B) 25%
(C) 50%
(D) 100%
Answer: (C) 50%
Explanation: A heterozygous affected parent can transmit either A or a, whereas an unaffected aa parent transmits only a. Thus half the children are predicted Aa and half aa. The 50% risk applies independently to each pregnancy under the stated assumptions.
Q31. A mother carries one mutant allele for an X-linked recessive disease, and the father is unaffected. What is the risk that a son is affected?
(A) 0%
(B) 25%
(C) 50%
(D) 100%
Answer: (C) 50%
Explanation: Sons inherit a Y chromosome from their father and their single X chromosome from their mother. A carrier mother passes the mutant X to approximately half her sons, so each son has a 50% chance of expressing an X-linked recessive disorder.
