Quiz Tweek

Preparing your workspace...

CBSE Class 12 Biology (Genetics) Quiz Principles of Inheritance and Variation Set-6 MCQ Online Practice Test | Class 12 | Quiz Tweek

CBSE Class 12 Biology (Genetics) Quiz Principles of Inheritance and Variation Set-6

Practice Important MCQs for Principles of Inheritance and Variation — Biology, Class 12.

This chapter is foundational for understanding how traits are passed from parents to offspring and how genetic variation arises. Board and competitive exams frequently test concepts like recombination frequency, linkage and gene mapping, lethal alleles, incomplete dominance, and X-linked inheritance—often using standard test cross and pedigree-based reasoning. Strong command of these problems helps you quickly identify inheritance patterns and calculate genetic distances accurately.

Minutes

Questions

1 / -0

Marking

Question Bank Preview

Q1. In a test cross of a dihybrid F1 (AaBb) with a homozygous recessive tester, 320 parental-type progeny and 80 recombinant-type progeny were observed among 400 offspring. Using the relation $RF=\dfrac{R}{T}\times 100$ , the map distance between the two genes is:

(A)

10 cM

(B)

20 cM

(C)

25 cM

(D)

40 cM

Q2. A man with blood group AB and a woman with blood group O have a child who is phenotypically blood group O. Considering the H locus (Bombay phenotype) where genotype $hh$ masks ABO antigens, which of the following parental genotypes could explain this observation?

(A)

Father $I^{A}I^{B}\;HH$ , Mother $ii\;Hh$

(B)

Father $I^{A}I^{B}\;Hh$ , Mother $ii\;HH$

(C)

Father $I^{A}I^{B}\;Hh$ , Mother $ii\;Hh$

(D)

Father $I^{A}I^{B}\;HH$ , Mother $ii\;HH$

Q3. In a strain of mice pigment is determined by allele $C$ (pigmented) and $c$ (albino recessive), but the homozygous $CC$ genotype is embryonically lethal. A cross $Cc \times Cc$ is performed. What fraction of surviving offspring will be pigmented?

(A)

$\dfrac{2}{3}$

(B)

$\dfrac{1}{2}$

(C)

$\dfrac{3}{4}$

(D)

$\dfrac{1}{3}$

Q4. Assertion: The recombination frequency (RF) between two loci is directly proportional to their physical separation measured in base pairs; doubling the base‑pair distance will always double the RF.
Reason: Recombination events are non‑uniform along chromosomes because of interference and recombination hotspots; RF is a measure of genetic map distance (in centiMorgans) rather than a strict linear measure of physical base pairs. Recombination frequency is calculated as $RF=\dfrac{R}{T}\times 100$ .

(A)

Both assertion and reason are true, and reason correctly explains the assertion.

(B)

Both assertion and reason are true, but reason does not correctly explain the assertion.

(C)

Assertion is true but reason is false.

(D)

Assertion is false but reason is true.

Q5. In a testcross of a trihybrid (heterozygous for three linked genes) with a homozygous recessive tester the following progeny numbers were obtained: $ABC:450,\ ABc:25,\ AbC:10,\ Abc:30,\ aBC:20,\ aBc:20,\ abC:15,\ abc:430$ . Using $r_{XY}=\dfrac{\text{recombinants between }X\text{ and }Y}{\text{total progeny}}\times 100$ , the most likely gene order and map distances (in cM) between adjacent genes are:

(A)

Order A–C–B; $AC=9\ \text{cM},\ CB=7\ \text{cM}$

(B)

Order A–B–C; $AB=8\ \text{cM},\ BC=7\ \text{cM}$

(C)

Order B–A–C; $BA=8\ \text{cM},\ AC=9\ \text{cM}$

(D)

Order A–B–C; $AB=8\ \text{cM},\ BC=8\ \text{cM}$

Q6. In a species, flower colour shows incomplete dominance: $RR$ = red, $rr$ = white and $Rr$ = pink. Two pink plants are crossed. What fraction of their F2 progeny will display the red phenotype?

(A)

$\dfrac{1}{2}$

(B)

$\dfrac{1}{3}$

(C)

$\dfrac{1}{4}$

(D)

$\dfrac{3}{4}$

Q7. In a test cross between a dihybrid plant $(AB/ab)$ and a homozygous recessive $(ab/ab)$ the progeny counts observed were: $AB=460,\ ab=440,\ Ab=45,\ aB=55$ . The map distance between genes A and B (in cM) is approximately:

(A)

$5\ \text{cM}$

(B)

$10\ \text{cM}$

(C)

$15\ \text{cM}$

(D)

$20\ \text{cM}$

Q8. Consider a trait in a human family with these features: affected fathers do not transmit the trait to their sons but transmit to all daughters who are phenotypically normal (carriers); those carrier daughters sometimes have affected sons; the trait appears much more frequently in males than females. Which inheritance pattern best fits these observations?

(A)

Autosomal dominant

(B)

Autosomal recessive

(C)

X-linked dominant

(D)

X-linked recessive

Q9. Assertion (A): A cross between two heterozygotes for a dominant allele that is homozygous lethal produces an observed phenotypic ratio of $2:1$ among viable progeny.
Reason (R): Homozygous dominant embryos die before birth, removing one genotype class from the expected $1:2:1$ genotypic ratio.
Which of the following is correct?

(A)

Both A and R are true and R is the correct explanation of A.

(B)

Both A and R are true but R is not the correct explanation of A.

(C)

A is true but R is false.

(D)

A is false but R is true.

Q10. In a three-point test cross the recombination frequencies are $r_{AB}=10\%$ and $r_{BC}=5\%$ . The observed frequency of double crossovers is $0.2\%$ . Interference is defined as $I=1-\dfrac{\text{observed double crossovers}}{\text{expected double crossovers}}$ . The value of interference (approximately) is:

(A)

$40\%$

(B)

$60\%$

(C)

$80\%$

(D)

$20\%$

Q11. A plant of genotype AaBb is crossed with Aabb. Assuming independent assortment, what proportion of the progeny will be heterozygous for both genes?

(A)

$1/8$

(B)

$1/4$

(C)

$1/2$

(D)

$3/8$

Q12. In a test cross RrYy × rryy the progeny numbers obtained are: RY = 420, ry = 400, Ry = 80, rY = 100. What is the recombination frequency between the R and Y loci (in centiMorgans)?

(A)

$9\%$

(B)

$36\%$

(C)

$82\%$

(D)

$18\%$

Q13. A woman with blood group A whose father is blood group O marries a man with blood group B whose mother is AB and father is O. What is the probability that their first child will have blood group O?

(A)

$1/4$

(B)

$1/2$

(C)

$1/8$

(D)

$0$

Q14. In a three‑point test cross the map distances between A–B and B–C are $10\ \mathrm{cM}$ and $5\ \mathrm{cM}$ respectively. Out of $N=2000$ progeny, the observed number of double crossovers is 8. Calculate the coefficient of coincidence (CoC) and the interference (I).

(A)

$\mathrm{CoC}=0.5,\ \mathrm{Interference}=0.5$

(B)

$\mathrm{CoC}=0.4,\ \mathrm{Interference}=0.6$

(C)

$\mathrm{CoC}=0.8,\ \mathrm{Interference}=0.2$

(D)

$\mathrm{CoC}=1.25,\ \mathrm{Interference}=-0.25$

Q15. In Labrador retrievers coat colour is determined by two genes: $B/b$ (black/brown; $B$ dominant) and $E/e$ (pigment deposition; $e/e$ is epistatic giving yellow regardless of $B$ ). Two black dogs are mated and produce 270 black, 90 brown and 120 yellow puppies. What are the most likely genotypes of the parents?

(A)

Both parents are $BBee$

(B)

Both parents are $BbEe$

(C)

One parent $BbEE$ and the other $BbEe$

(D)

Both parents are $Bbee$

More Quizzes for Class 12

Explore other chapters and subjects, or view all quizzes for this class.

Quiz Tweek

CBSE Class 12 Biology (Genetics) Quiz Principles of Inheritance and Variation Set-6

Question Bank Preview

More Quizzes for Class 12

Chemistry

Mathematics

Physics