This set of Advanced Cytogenetics Questions and Answers focuses on “Chromosomal Abnormalities : Aneuploidy”.
1. In aneuploidy the entire set of chromosome is not involved in duplication of deletion.
Explanation: In aneuploidy the change is in one or two chromosomes and not an increase or decrease of an entire set. This makes it different from euploidy.
2. If an organism has 14 chromosomes, the number of chromosome generated by nullisomy will be_____________________
Explanation: Nullisomy results in (2n-2) set of chromosome, here n=7, so it will result in 12 chromosome over all.
3. Turner’s syndrome is a result of _________________
Explanation: In Turner’s syndrome one set of sex chromosmome is lost resulting in 44+XO females who have masculine condition. This is a result of monosomy.
4. Aneuploidy is usually deleterious as _________________
a) Chromosomal pairing is hampered
b) Gene balance is disrupted
c) Size of individual may vary
d) Chromosomal disintegration is increased
Explanation: In case of aneuploidy there is loss or gain in single chromosome which results in dis-balance of the genes and their products. This is a reason that aneuploids are usually lethal.
5. Which of the following is an example of trisomy ________________
Explanation: Klinefelter syndrome results from trisomy in sex chromosome producing 44+ XXY. Turner is due to monosomy, endosperm is triploid i.e. the complete set of chromosome is increased and XP is due to mutation or deletion in gene not entire chromosome.
6. ________________ aneuploidy is better tolerated.
c) Sex chromosomal
d) Chromosome 13
Explanation: In case of sex chromosome due to dosage compensation in female one of X chromosome is inactivated. This is similar to the absence of a sex chromosome, which makes sex chromosome aneuploidy less lethal.
7. Patau syndrome is a result of which of the following?
a) Non-disjunction of sex chromosome in female
b) Non- disjunction of sex chromosome in male
c) Non-disjunction of chromosome 21
d) Non-disjunction of chromosome 13
Explanation: Non-disjunction of chromosome 13 will result in a trisomy and monosomy if the gamete is fertilized. This results in Pataeu syndrome. It is an autosomal aneuploidy.
8. The probability of aneuploidy in offspring increases with age as _________________
a) Chromosomes tend to lose information with age
b) Pairings at dichtyotene stages are gradually lost
c) Ability of fertilization with age is gradually lost
d) Chromosomal aberration with age
Explanation: The chromosomes with age tend to lose the proper pairings that existed when they were in dictyotene stage as this is prolonged over decades. This leads to improper segregation causing trisomy.
9. A non-disjunction in the 1st phase of meiosis will lead to ______________
Explanation: Nullysomy in chromosome is a loss of 2 chromosomes i.e. loss of a chromosomal pair. This can result from passing of both homologous chromosomes to the same pole during meiosis 1- this pole will produce trisomic gametes while the counterpart will produce nullisomic gametes.
10. At what maternal age the probability of having a child with Down’s syndrome is increased drastically?
Explanation: After the age of 35 the probability of non-disjunction in gamete leading to Down’s syndrome increases to 1/290. With increasing age it increases still further.
11. Chromosome ____________ trisomy leads to Edward’s syndrome.
Explanation: Chromosome 18 trisomy will lead to Edward’s syndrome. Trisomy in chromosome 13 and 21 leads to Patau and Down’s syndrome respectively.
12. Sexual mosaics lead to formation of _______________
a) Female from male egg
Explanation: In case of sexual mosaics there is loss in one of the sex chromosomes in some cells. In case of male there will thus be a mosaic of male and female parts corresponding to XY and XO depending on which part has which combination.
13. Extreme klinefelter is an example of _____________________
Explanation: In extreme klinefelter the chromosomal constitution is 44+XXXY, there are two extra X chromosomes which leads to more severe Klinefelter condition. Thus, it is tetrasomy.
14. Choose the wrong statement.
a) Maternal trisomy in a gamete is more severe in paternal gamete trisomy
b) Tetrasomy and nullisomy are due to change in chromosome number by 2
c) Disomy has severe effects
d) Edward’s syndrome is due to trisomy of chromosome 18
Explanation: Disomy is nothing other than the normal chromosome numbers; this is having no harmful effect. The option a, b and d are however true.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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