Crosses that break the Mendelian ratio — NEET & JEE Questions

Question 1 · difficulty L1 · recall

A single gene influencing multiple phenotypic traits:

• A. codominance
• B. polygenic inheritance
• C. linkage
• D. pleiotropy

Question 2 · difficulty L1 · recall

The ABO blood group phenotype showing simultaneous expression of IA and IB:

• A. O
• B. A
• C. B
• D. AB

Question 3 · difficulty L1 · recall

The number of common alleles in the human ABO blood-group system:

• A. one
• B. three
• C. four
• D. two

Question 4 · difficulty L2 · understanding

The F2 phenotypic ratio in a classic incomplete-dominance monohybrid cross:

• A. 3:1
• B. 2:1
• C. 9:3:3:1
• D. 1:2:1

Question 5 · difficulty L2 · understanding

Incomplete dominance differs from complete dominance because the heterozygote

• A. shows an intermediate phenotype
• B. always matches the dominant homozygote
• C. always matches the recessive homozygote
• D. has no phenotype

Question 6 · difficulty L2 · understanding

In codominance, a heterozygote typically

• A. expresses both alleles distinctly
• B. expresses only the dominant allele
• C. expresses neither allele
• D. always shows an intermediate blended phenotype

Question 7 · difficulty L3 · application

In a cross between red-flowered and white-flowered snapdragons, the F1 plants are pink. What inheritance pattern is illustrated?

• A. Complete dominance with full masking of one allele
• B. Incomplete dominance
• C. Codominance
• D. Sex linkage

Question 8 · difficulty L3 · understanding

What is the probability of having children with 'O' blood group, where both mother and father are heterozygous for ' $\underline{\mathrm{A}}$ ' and ' $\underline{\mathrm{B}}$ ' blood group, respectively?

• A. $25 \%$
• B. $0 \%$
• C. $75 \%$
• D. $50 \%$

Question 9 · difficulty L3 · understanding

Given below are two statements: Statement I: When many alleles of a single gene govern a character, it is called polygenic inheritance. Statement II: In Polygenic inheritance, the effect of each allele is additive. In the light of the above statements, choose the correct answer from the options given below.

• A. Statement I is true but Statement II is false
• B. Statement I is false but Statement II is true
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Question 10 · difficulty L3 · understanding

The mother has $$\mathrm{A}+$$ blood group the father has $$\mathrm{B}+$$ and the child is $$\mathrm{A}+$$. What can be the possibility of genotypes of all three, respectively? A. $$I^A I^A|I B i| I^B i$$ B. $$I^A I^A\left|I^B i\right| I^A i$$ C. $$I^B i\left|I^A I^A\right| I^A I^B$$ D. $$\left|A \beta^A\right| I^B I^B \mid I^A i$$ E. $$I^A i\left|I^B i\right| I^A i$$ Choose the correct answer from the option given below:

• A. C and D
• B. D and A
• C. A and B
• D. B and E