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Genetics

Mendelian Genetics Practice Questions

19 free Mendelian Genetics 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 19 Medium

According to Mendel's Law of Segregation, what happens to the two alleles for a trait during the formation of gametes?

  1. A They combine to form a new intermediate allele
  2. B They stay together in every gamete
  3. C They segregate into separate gametes
  4. D One allele is destroyed to ensure haploidy

Correct answer: They segregate into separate gametes

Mendel's first law states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. This ensures that each offspring receives one factor from each parent, maintaining the diploid number.

Question 2 of 19 Medium

In a monohybrid cross between a homozygous dominant (YY) tall plant and a homozygous recessive (yy) short plant, what is the phenotype of the F1 generation?

  1. A All short
  2. B All tall
  3. C Medium
  4. D 3:1 ratio

Correct answer: All tall

The F1 generation will all have the genotype Yy. Since the tall trait is dominant over the short trait, the presence of one dominant allele (Y) results in the tall phenotype for all offspring.

Question 3 of 19 Medium

What is the expected phenotypic ratio of a dihybrid cross between two individuals heterozygous for both traits (AaBb x AaBb)?

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

Correct answer: 9:3:3:1

A dihybrid cross involving two heterozygous parents typically results in a 9:3:3:1 ratio. This ratio represents the combinations of dominant and recessive phenotypes for two independent traits.

Question 4 of 19 Medium

A test cross is used to determine the genotype of an individual with a dominant phenotype. With what genotype is this individual crossed?

  1. A Homozygous dominant
  2. B Heterozygous
  3. C Homozygous recessive
  4. D Hemizygous

Correct answer: Homozygous recessive

Crossing the unknown dominant individual with a homozygous recessive individual reveals the genotype. If any recessive offspring appear, the unknown parent must be heterozygous.

Question 5 of 19 Medium

If a plant with genotype RrYy is self-pollinated, what is the probability of obtaining an offspring with the genotype rryy?

  1. A 1/4
  2. B 1/8
  3. C 1/16
  4. D 9/16

Correct answer: 1/16

The probability of 'rr' is 1/4 and the probability of 'yy' is 1/4. Using the product rule for independent events, 1/4 multiplied by 1/4 equals 1/16.

Question 6 of 19 Medium

Mendel's Law of Dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. What is the hidden trait called?

  1. A Dominant
  2. B Recessive
  3. C Codominant
  4. D Incomplete

Correct answer: Recessive

The recessive allele is only expressed phenotypically when the individual is homozygous for that allele. In a heterozygous state, the dominant allele masks the expression of the recessive allele.

Question 7 of 19 Medium

In peas, yellow seeds (Y) are dominant over green seeds (y). If a yellow-seeded plant is crossed with a green-seeded plant and half of the offspring are green, what was the genotype of the yellow parent?

  1. A YY
  2. B Yy
  3. C yy
  4. D YYyy

Correct answer: Yy

For green offspring (yy) to be produced, both parents must contribute a 'y' allele. Since the yellow parent shows the dominant trait but produced recessive offspring, it must be heterozygous (Yy).

Question 8 of 19 Medium

How many different types of gametes can be produced by an individual with the genotype AaBbCc?

  1. A 3
  2. B 6
  3. C 9
  4. D 8

Correct answer: 8

The number of gamete types is calculated using the formula 2^n, where n is the number of heterozygous gene pairs. Here, 2^3 equals 8 unique gametic combinations.

Question 9 of 19 Medium

Which of the following represents a dihybrid cross?

  1. A TT x tt
  2. B Tt x Tt
  3. C TTRr x ttrr
  4. D TtRr x TtRr

Correct answer: TtRr x TtRr

A dihybrid cross involves two organisms that are identically hybrid for two traits. This is represented by crossing two individuals with the genotype TtRr.

Question 10 of 19 Medium

In a cross between AaBb and aabb, what is the expected phenotypic ratio of the offspring?

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

Correct answer: 1:1:1:1

This is a dihybrid test cross. Because one parent produces four types of gametes and the other only one type of recessive gamete, the offspring will appear in a 1:1:1:1 ratio.

Question 11 of 19 Medium

Which term describes an individual possessing two different alleles for a particular gene?

  1. A Heterozygous
  2. B Homozygous
  3. C Hemizygous
  4. D Dihybrid

Correct answer: Heterozygous

Heterozygous individuals have one dominant and one recessive allele (e.g., Aa). This differs from homozygous individuals, who have two identical alleles (e.g., AA or aa).

Question 12 of 19 Medium

Mendel used the term 'factors' to describe the units of inheritance. What do we call these factors today?

  1. A Alleles
  2. B Proteins
  3. C Traits
  4. D Genes

Correct answer: Genes

The 'factors' Mendel identified are now known as genes, which are specific sequences of DNA located on chromosomes that code for particular traits.

Question 13 of 19 Medium

If two traits are linked on the same chromosome and located very close to each other, which of Mendel's laws do they violate?

  1. A Law of Segregation
  2. B Law of Dominance and Recessiveness
  3. C Law of Purity of Gametes
  4. D Law of Independent Assortment

Correct answer: Law of Independent Assortment

The Law of Independent Assortment assumes genes are on different chromosomes. Linked genes tend to be inherited together, which prevents them from assorting independently unless crossing over occurs.

Question 14 of 19 Medium

What is the probability of a cross between Rr and Rr producing a homozygous dominant offspring?

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

Correct answer: 25%

A Punnett square for Rr x Rr results in 1/4 RR, 1/2 Rr, and 1/4 rr. Therefore, there is a 25% chance of the offspring being homozygous dominant (RR).

Question 15 of 19 Medium

In Mendelian genetics, the physical appearance of an organism is called its:

  1. A Phenotype
  2. B Genotype
  3. C Allele
  4. D Locus

Correct answer: Phenotype

The phenotype is the observable physical or physiological trait of an organism, determined by its genetic makeup (genotype) and environmental influences.

Question 16 of 19 Medium

During which phase of meiosis does the physical basis for the Law of Segregation occur?

  1. A Anaphase I
  2. B Prophase I
  3. C Metaphase II
  4. D Anaphase II

Correct answer: Anaphase I

During Anaphase I, homologous chromosomes (each carrying one allele of a gene) are pulled to opposite poles. This ensures each daughter cell receives only one of the two alleles.

Question 17 of 19 Medium

If you cross a true-breeding purple-flowered plant with a true-breeding white-flowered plant and all F1 are purple, what is the ratio of purple to white in the F2 generation?

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

Correct answer: 3 purple : 1 white

The F1 plants are all heterozygous. When F1 plants (Pp) are self-crossed, the resulting F2 generation follows a 3:1 phenotypic ratio of dominant to recessive traits.

Question 18 of 19 Medium

A cross is performed between AABB and aabb. What will be the genotype of the F1 generation?

  1. A AaBb
  2. B AABB
  3. C aabb
  4. D Aabb

Correct answer: AaBb

The parent AABB produces gametes AB, and aabb produces gametes ab. The union of these gametes results in F1 offspring with the heterozygous genotype AaBb.

Question 19 of 19 Medium

How many squares are required in a Punnett square to analyze a trihybrid cross between two triple heterozygotes (AaBbCc)?

  1. A 4
  2. B 16
  3. C 32
  4. D 64

Correct answer: 64

Each parent produces 8 types of gametes (2^3). An 8x8 grid is needed to account for all possible combinations, resulting in 64 squares.

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