15 extra multiple-choice questions for Principles of Inheritance and Variation (12th Standard Zoology, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
What term is used to describe individuals who secrete ABO blood group antigens in their bodily fluids, such as saliva?
- A. Non-secretors
- B. SecretorsCorrect
- C. Null individuals
- D. Carriers
Explanation. Individuals who possess A and B antigens in their bodily fluids, including saliva, are termed secretors.
Q2
Why is the IO allele of the ABO blood group system referred to as a null allele?
- A. It produces an inactive form of N-acetyl galactose transferase.
- B. It lacks any chromosomal locus on the homologous chromosomes.
- C. It does not produce any active terminal transferase enzyme to add sugars to the precursor.Correct
- D. It encodes a defective galactose transferase that degrades H substances.
Explanation. The IO allele does not produce terminal transferase, making it unable to attach N-acetyl galactosamine or galactose to the precursor substance.
Q3
According to the text, what is the size of the human Y chromosome and the number of functional genes it carries?
- A. 165 Mb in size with about 1,000 genes
- B. 60 Mb in size with 60 functional genesCorrect
- C. 60 Mb in size with about 1,000 genes
- D. 165 Mb in size with 60 functional genes
Explanation. The human Y chromosome spans 60 Mb and contains 60 functional genes, while the larger X chromosome is 165 Mb with approximately 1,000 genes.
Q4
Individuals with homomorphic sex chromosomes are characterized by which of the following features?
- A. They produce two distinct types of gametes and are heterogametic.
- B. They possess dissimilar sex chromosomes and are homogametic.
- C. They produce only one type of gametes and are homogametic.Correct
- D. They possess dissimilar sex chromosomes and are heterogametic.
Explanation. Homomorphic sex chromosomes are identical in shape and structure. Individuals possessing them are homogametic, producing only a single type of gamete.
Q5
Which type of sex determination mechanism is exhibited by domestic chickens?
- A. XX-XY type
- B. ZO-ZZ typeCorrect
- C. ZW-ZZ type
- D. XX-XO type
Explanation. Domestic chickens, along with moths and butterflies, exhibit the ZO-ZZ system of sex determination, where females are ZO and males are ZZ.
Q6
Which region of the human Y chromosome shares homology with the X chromosome and undergoes synapsis and recombination during meiosis?
- A. SRY gene region
- B. Non-homologous region
- C. Pseudoautosomal regions (PARs)Correct
- D. Holandric regions
Explanation. The pseudoautosomal regions located at both ends of the Y chromosome are homologous to X chromosome regions, allowing pairing and recombination during meiosis.
Q7
In which organism and cell type did Barr and Bertram first observe the condensed sex chromatin body?
- A. Red blood cells of a female human
- B. Nerve cells of a female catCorrect
- C. Epithelial cells of a male Drosophila
- D. Salivary gland cells of a female mouse
Explanation. Barr and Bertram first discovered sex chromatin in 1949 as a condensed body within the nerve cells of a female cat.
Q8
What evolutionary term describes the behavior where sterile diploid worker honeybees raise the queen's eggs to support her reproductive success?
- A. Natural selection
- B. Kin selectionCorrect
- C. Sexual selection
- D. Artificial selection
Explanation. Diploid worker bees help raise the queen's offspring to promote the survival of shared genes, a process known as kin selection.
Q9
Cytoplasmic or extrachromosomal inheritance in animals is traditionally studied using which of the following model organisms?
- A. Drosophila melanogaster eye color
- B. Shell coiling in Limnaea and kappa particles in ParameciumCorrect
- C. Sickle cell traits in human lineages
- D. Red-green color blindness in mammals
Explanation. Cytoplasmic inheritance does not follow Mendelian patterns and is classically studied via shell coiling in Limnaea and kappa particles in Paramecium.
Q10
Why is hypertrichosis of the ear pinna in humans transmitted strictly from fathers to their sons?
- A. It is an autosomal dominant trait that is suppressed in females.
- B. It is determined by a holandric gene located on the non-homologous region of the Y chromosome.Correct
- C. It is an X-linked recessive trait with high penetrance in males.
- D. It is a mitochondrial trait inherited through maternal cytoplasm.
Explanation. Hypertrichosis is caused by holandric genes on the Y chromosome, which males inherit directly from their fathers.
Q11
Which of the following represents the normal polypeptide chain composition of a human hemoglobin molecule?
- A. Four alpha globin chains
- B. Two alpha and two beta globin chainsCorrect
- C. Four beta globin chains
- D. One alpha and three beta globin chains
Explanation. Normal human adult hemoglobin is a tetramer made up of two alpha globin chains and two beta globin chains.
Q12
What does the term Euphenics refer to in the context of improving the human race?
- A. The elimination of defective germplasm through sterilization and selective immigration.
- B. The symptomatic treatment of genetic diseases, also known as medical engineering.Correct
- C. The improvement of the human race by enhancing environmental conditions like nutrition.
- D. The selection of desirable genotypes by encouraging early marriages.
Explanation. Euphenics, or medical engineering, deals with treating the symptoms of inherited genetic disorders, such as inborn errors of metabolism.
Q13
Who coined the term Euphenics in 1960 to describe the control of inherited human diseases?
- A. Francis Galton
- B. Gregor Mendel
- C. Joshua LederbergCorrect
- D. Karl Pearson
Explanation. The term Euphenics, meaning normal appearing, was coined by Joshua Lederberg in 1960 to describe medical engineering for genetic diseases.
Q14
Which science focuses on the improvement of the human race by providing better nutrition, unpolluted ecological conditions, and education?
- A. Eugenics
- B. Euphenics
- C. EuthenicsCorrect
- D. Genomics
Explanation. Euthenics is the science of improving the human species by modifying environmental factors like nutrition, pollution, and education.
Q15
Who is recognized as the founder of the modern Eugenics movement?
- A. Gregor Mendel
- B. Charles Darwin
- C. Francis GaltonCorrect
- D. Joshua Lederberg
Explanation. Francis Galton is recognized as the founder of the modern eugenics movement, which applies genetic laws to improve human traits.
Frequently asked questions
How many MCQs are there in Principles of Inheritance and Variation?
This chapter has 15 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Zoology MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Principles of Inheritance and Variation book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
