Biology Questions and Answers – Inheritance and Variation Principles – Mendelian Disorders

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This set of Biology Multiple Choice Questions & Answers (MCQs) focuses on “Inheritance and Variation Principles – Mendelian Disorders”.

1. People suffering from colour blindness fail to distinguish which of the two colours?
a) Red and Green
b) Blue and Green
c) Red and Blue
d) Red and Yellow
View Answer

Answer: a
Explanation: People who are colour blind fail to distinguish between red and green colours. Colour blindness is a sex-linked recessive trait in which the normal gene and its recessive allele are carried by X-chromosome.
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2. When can a female be colour blind?
a) Father has normal vision and the mother is a carrier
b) Father has normal vision and mother is colour blind
c) Father is colour blind and the mother has a normal vision
d) Father is colour blind and mother is a carrier
View Answer

Answer: d
Explanation: A female can be a colour blind only in two conditions:
i. When her father is colour blind and her mother is the carrier of this disease
ii. When both her father and her mother are colour blind
Therefore, for a female to be colour blind, her father must also have colour blindness.

3. Which of the following type of inheritance is shown by colour blindness?
a) Chromosomal inheritance
b) Criss-cross inheritance
c) Zig-zag inheritance
d) Up-down inheritance
View Answer

Answer: b
Explanation: Colour-blindness is a sex-linked trait which shows criss-cross inheritance which means male transmits his trait to his grandson through his daughter, while a female transmits the traits to her granddaughter through her son.
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4. What will be the percentage of sons having a normal vision if the father has normal vision and their mother is colour blind?
a) 0%
b) 25%
c) 50%
d) 100%
View Answer

Answer: a
Explanation: The percentage of sons having normal vision, if the father has normal vision and mother is colour blind is 0% because as colour blindness is a sex-linked trait, it means that the trait only transmits through X-chromosome. As the mother is colour blind, both her gametes will carry the gene for colour blindness, so none of their sons will have a normal vision.

5. What percentage of children are colour blind if their father is colour blind and the mother is a carrier for Colour blindness?
a) 25%
b) 50%
c) 75%
d) 100%
View Answer

Answer: b
Explanation: The percentage of children which are colour blind if their father is colour blind and the mother is a carrier for colour blindness is 50% because the father will produce Xc and Y chromosome and the mother will produce Xc and X chromosomes. Their children will have the genotypes- XcY, XY, XcXc and XcX. Therefore, 50% of children are colour blind, 25% have normal vision and 25% are the carriers of the disease.
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6. Haemophilia is an autosomal recessive trait.
a) True
b) False
View Answer

Answer: b
Explanation: No, haemophilia is not an autosomal recessive trait. It is X-linked recessive trait and shows transmission from normal carrier female to a male progeny. In this disease, the exposed blood of affected individuals cannot coagulate due to the presence of defective blood clotting factors.

7. How can a female be haemophilic?
a) Mother is haemophilic and father is normal
b) Mother is a carrier and father is haemophilic
c) Both mother and father are carriers
d) Both mother and father are haemophilic
View Answer

Answer: b
Explanation: A female can only be haemophilic if her mother is at least a carrier of this disease and her father is haemophilic. But the possibility of a female becoming haemophilic is extremely rare because being haemophilic for the parents at the later stage of life is unviable.
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8. What is the full form of AHG?
a) Anti haemophilic globulin
b) Anti haemoglobin
c) Allergic haemoglobin
d) Allergic haemophilic globulin
View Answer

Answer: a
Explanation: AHG stands for Anti haemophilic globulin. It is a type of blood protein which is required for normal blood clotting. The person suffering from haemophilia A cannot synthesise this protein and even a small cut may lead to continuous bleeding for a long time.

9. What is the percentage of children being a carrier of haemophilia if their mother is a carrier and their father is a normal man?
a) 25%
b) 50%
c) 75%
d) 100%
View Answer

Answer: a
Explanation: The percentage of children being a carrier of haemophilia if their mother is a carrier and their father is a normal man is 25% because the gametes formed by mother are X and Xh while the gametes formed by father are X and Y. The genotype of the offspring obtained would be XY, XX, XXh and XhY. Thus 50% of children are normal, 25% are carriers of haemophilia and 25% are haemophilic (only son).
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10. How many genotypes of sickle cell anaemia are possible in a population?
a) One
b) Two
c) Three
d) Four
View Answer

Answer: c
Explanation: Three types of genotypes of sickle cell anaemia are possible in a population. These are:
i. HbA HbA: Normal individuals
ii. HbA HbS: Normal individuals but act as a carrier in spreading the disease
iii. HbS HbS: Diseased individuals and they die before attaining maturity

11. Heterozygous individuals of sickle cell anaemia are severely affected by the disease.
a) False
b) True
View Answer

Answer: a
Explanation: No, heterozygous individuals of sickle cell anaemia are not severely affected by the disease. Apparently, they appear to be unaffected by the disease. But, there is a 50% probability of transmission of the mutant gene to the progeny.

12. Which of the following statements are correct with respect to the figures given?
Normal RBCs diagram
a) 1 represents normal WBCs
b) 1 represents normal RBCs
c) 2 represents abnormal RBCs
d) 2 represents normal RBCs
View Answer

Answer: b
Explanation: 1st figure represents the micrograph of RBCs from a normal individual while the 2nd figure represents the micrograph of RBCs from an individual affected with sickle-cell anaemia. The RBCs of a normal individual are biconcave shaped while that of sickle cell anaemia are elongated sickle-like structure.

13. In which of the following places thalassemia is not common?
a) Indian subcontinent
b) South-east Africa
c) Mediterranean
d) North America
View Answer

Answer: d
Explanation: Thalassemia is not common in North America. It is common in the Middle East, Indian subcontinent, Mediterranean and South-east Africa. It originated in the Mediterranean region and is caused by the deletion or mutation of the chromosomes.

14. By which of the following defects, thalassemia is caused?
a) Defects in RBCs
b) Defects in WBCs
c) Defects in platelets
d) Defects in lymphocytes
View Answer

Answer: a
Explanation: The defect in the synthesis of globin polypeptide in RBC causes a group of disorders known as thalassemia. Absence or reduced synthesis of one of the globin chains leads to the excess of other chains which accumulate in our body to causes different diseases.

15. Which of the following statements is incorrect with respect to alpha-thalassemia?
a) Involves the genes HBA1 and HBA2
b) Inherited in a Mendelian dominant fashion
c) Connected to the deletion of the 16p chromosome
d) Result in decreased α-globin production
View Answer

Answer: b
Explanation: Alpha-thalassemia is not inherited in a Mendelian dominant fashion. Instead, it is inherited in a Mendelian recessive fashion. It involves the genes HBA1 and HBA2 and it is also connected to the deletion of the 16p chromosome.

16. Which of the chromosome mutation leads to Beta-thalassemia?
a) 21
b) 10
c) 11
d) 13
View Answer

Answer: c
Explanation: The mutation in the HBB gene on chromosome number 11 leads to the disorder beta-thalassemia. It is inherited as an autosomal recessive trait. The severity of beta-thalassemia depends upon the nature of the mutation.

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