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Genetics

Non-Mendelian Inheritance Practice Questions

20 free Non-Mendelian Inheritance practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

In a cross between a red-flowered snapdragon and a white-flowered snapdragon, all F1 offspring are pink. This is an example of:

  1. A Incomplete dominance
  2. B Codominance
  3. C Pleiotropic gene action
  4. D Multiple alleles

Correct answer: Incomplete dominance

Incomplete dominance occurs when the phenotype of the heterozygote is an intermediate blend of the two homozygotes. In snapdragons, neither red nor white is fully dominant, resulting in pink flowers.

Question 2 of 20 Medium

Which of the following best describes codominance?

  1. A The dominant allele completely masks the recessive allele
  2. B The offspring show a blend of parental traits
  3. C Both alleles are fully expressed in the heterozygote
  4. D A single gene affects multiple unrelated phenotypic traits

Correct answer: Both alleles are fully expressed in the heterozygote

Codominance is characterized by the independent and distinct expression of both alleles in a heterozygous individual. A classic example is the AB blood type, where both A and B antigens are present.

Question 3 of 20 Medium

The human ABO blood group system, specifically the AB blood type, is a classic example of:

  1. A Incomplete dominance
  2. B Pleiotropy
  3. C Polygenic inheritance
  4. D Codominance

Correct answer: Codominance

In individuals with genotype IAIB, both the A and B alleles are expressed equally on the surface of red blood cells. Since neither allele masks the other, it defines codominance.

Question 4 of 20 Medium

Sickle cell anemia, where a single genetic mutation affects hemoglobin shape, physical stamina, and resistance to malaria, is an example of:

  1. A Incomplete dominance
  2. B Epistasis
  3. C Complementary genes
  4. D Pleiotropy

Correct answer: Pleiotropy

Pleiotropy occurs when one single gene influences multiple, seemingly unrelated phenotypic traits. In sickle cell anemia, the mutation in the beta-globin gene causes various physiological effects across different organ systems.

Question 5 of 20 Medium

If a pink-flowered snapdragon (RW) is crossed with another pink-flowered snapdragon (RW), what is the expected phenotypic ratio?

  1. A 1 Red : 2 Pink : 1 White
  2. B 3 Red : 1 White
  3. C All Pink
  4. D 9 Red : 3 Pink : 4 White

Correct answer: 1 Red : 2 Pink : 1 White

In cases of incomplete dominance, the phenotypic ratio matches the genotypic ratio. A cross of two heterozygotes results in 25% RR (red), 50% RW (pink), and 25% WW (white).

Question 6 of 20 Medium

Which condition is characterized by a single gene defect resulting in multiple symptoms like lens dislocation, long limbs, and cardiovascular issues?

  1. A Marfan syndrome
  2. B Cystic fibrosis
  3. C Huntington's disease
  4. D Phenylketonuria

Correct answer: Marfan syndrome

Marfan syndrome is a prime example of pleiotropy caused by a mutation in the FBN1 gene. This single mutation impacts connective tissue throughout the body, affecting the eyes, skeleton, and heart.

Question 7 of 20 Medium

In cattle, when a red bull is crossed with a white cow, the offspring are roan (hairs of both red and white). This inheritance pattern is:

  1. A Incomplete dominance
  2. B Codominant trait
  3. C Polygenic trait
  4. D Lethal alleles

Correct answer: Codominant trait

Roan coloration is an example of codominance because both red and white hairs are present and distinct. It is not a blend (which would be pink) but the expression of both parental colors together.

Question 8 of 20 Medium

How does incomplete dominance differ from Mendel’s Law of Dominance?

  1. A It follows a 3:1 phenotypic ratio in the F2 generation
  2. B The recessive allele is completely destroyed
  3. C Heterozygote phenotype differs from both parents
  4. D Heterozygotes always express the dominant trait

Correct answer: Heterozygote phenotype differs from both parents

Mendel's Law of Dominance suggests only the dominant phenotype appears in heterozygotes. Incomplete dominance deviates by producing a 'third' intermediate phenotype in the heterozygous state.

Question 9 of 20 Medium

In the case of lethal alleles in mice (yellow coat color), the yellow allele (Y) is dominant for coat color but recessive for lethality. What is the phenotypic ratio of living offspring from a cross between two yellow mice (Yy x Yy)?

  1. A 3 yellow : 1 agouti
  2. B 2 yellow : 1 agouti
  3. C 1 yellow : 2 agouti
  4. D All yellow

Correct answer: 2 yellow : 1 agouti

The homozygous dominant (YY) embryos die before birth. Among the surviving offspring, 2/3 are yellow (Yy) and 1/3 are agouti (yy), resulting in a 2:1 ratio.

Question 10 of 20 Medium

Which of the following is true regarding pleiotropy?

  1. A Multiple genes control one trait
  2. B Environment has no effect on the gene
  3. C A single gene affects multiple traits
  4. D Two alleles are expressed at the same time

Correct answer: A single gene affects multiple traits

Pleiotropy refers specifically to the phenomenon where a single gene locus affects more than one trait. This is common in many genetic disorders where one protein deficiency causes widespread bodily changes.

Question 11 of 20 Medium

Phenylketonuria (PKU) is a pleiotropic disorder. Which of the following is NOT a typical phenotypic effect of PKU?

  1. A Mental retardation
  2. B Reduced hair pigmentation
  3. C Reduced skin pigmentation
  4. D Increased muscle mass

Correct answer: Increased muscle mass

PKU is caused by a single gene mutation that prevents the breakdown of phenylalanine. This leads to various symptoms including skin/hair lightening and neurological issues, but not increased muscle mass.

Question 12 of 20 Medium

In a codominant system, if an individual with genotype 'LM LN' (M-N blood group) is crossed with 'LN LN', what percentage of offspring will be 'LN LN'?

  1. A 25%
  2. B 50%
  3. C 75%
  4. D 100%

Correct answer: 50%

The cross is MN x NN. The offspring genotypes will be 50% MN (LM LN) and 50% NN (LN LN).

Question 13 of 20 Medium

Which observation first suggested a deviation from Mendelian complete dominance?

  1. A Offspring appearing identical to the father
  2. B The F2 generation showing a 3:1 ratio
  3. C F1 offspring showing an intermediate phenotype
  4. D The disappearance of a trait for several generations

Correct answer: F1 offspring showing an intermediate phenotype

When F1 offspring showed phenotypes that were blends of the parents (like pink flowers from red and white), it signaled that the 'dominant' allele was not fully masking the 'recessive' one.

Question 14 of 20 Medium

Mendel’s pea experiments did not show incomplete dominance. If they had, a cross between tall (TT) and short (tt) plants would have produced:

  1. A All tall plants
  2. B All short plants
  3. C Plants of medium height
  4. D A 3:1 ratio of tall to short

Correct answer: Plants of medium height

Incomplete dominance results in a blend. If plant height followed this pattern, the heterozygous (Tt) offspring would exhibit a height intermediate between tall and short.

Question 15 of 20 Medium

Which statement about the ABO blood system is correct?

  1. A It shows incomplete dominance between A and B alleles
  2. B Allele i is codominant with allele IA
  3. C IA and IB are codominant, and both dominate over i
  4. D It is an example of pleiotropy only

Correct answer: IA and IB are codominant, and both dominate over i

The ABO system demonstrates both multiple alleles and codominance. IA and IB alleles are both expressed in the AB phenotype, but both behave as dominant over the recessive 'i' allele (Type O).

Question 16 of 20 Medium

Starch grain size in pea seeds shows incomplete dominance. If 'B' is for large grains and 'b' is for small grains, what size are the grains in 'Bb' seeds?

  1. A Very large
  2. B Very small
  3. C Intermediate
  4. D Unpredictable

Correct answer: Intermediate

While seed shape (round vs wrinkled) shows complete dominance, the actual starch grain size within the seed shows incomplete dominance, where heterozygotes have intermediate-sized grains.

Question 17 of 20 Medium

In Andalusian fowls, crossing black (BB) and white (bb) birds results in 'blue' (Bb) offspring. What is the phenotypic ratio of crossing two blue fowls?

  1. A All blue
  2. B 1 black : 2 blue : 1 white
  3. C 3 black : 1 white
  4. D 1 black : 1 blue : 2 white

Correct answer: 1 black : 2 blue : 1 white

This is a case of incomplete dominance. Self-crossing the heterozygotes (blue) yields a 1:2:1 ratio of black, blue, and white phenotypes respectively.

Question 18 of 20 Medium

If a gene has 3 different alleles in a population, how many alleles does a single diploid individual carry for that gene?

  1. A 1
  2. B 2
  3. C 3
  4. D 6

Correct answer: 2

Regardless of how many alleles exist in a population (multiple alleles), a diploid individual can only possess two alleles—one inherited from each parent.

Question 19 of 20 Medium

Which of the following is an example of environmental influence deviating from pure Mendelian expectations?

  1. A ABO blood group inheritance
  2. B Hydrangea color from soil pH
  3. C Pea plant flower color genetics
  4. D Hemophilia inheritance pattern

Correct answer: Hydrangea color from soil pH

Hydrangea color is determined by the acidity of the soil (pH), which affects aluminum availability. This shows that phenotype is not always a direct result of genotype alone but can be influenced by environmental factors.

Question 20 of 20 Medium

What is the genotypic ratio of the F2 generation in a monohybrid cross involving codominance?

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

Correct answer: 1:2:1

In both codominance and incomplete dominance, the F2 generation resulting from a monohybrid cross exhibits a 1:2:1 genotypic ratio, which is identical to the phenotypic ratio.

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