Dominant and Recessive Traits Quiz

What is a dominant allele?

• An allele that is only expressed when two copies are present

• An allele that is always expressed when present

• An allele that is never expressed

• An allele that is expressed only in the presence of a recessive allele

Answer explanation

A dominant allele is always expressed when present, meaning it will show its trait even if only one copy is present. This distinguishes it from recessive alleles, which require two copies to be expressed.

Which of the following is an example of a recessive trait?

• Brown eyes

• Blue eyes

• Freckles

• Dimples

Answer explanation

Blue eyes are a recessive trait, meaning they only appear when an individual inherits two copies of the blue eye allele. In contrast, brown eyes are dominant, and freckles and dimples are also typically dominant traits.

Using a Punnett square, predict the possible genotypes of offspring from parents with genotypes Aa and Aa.

• AA, Aa, Aa, aa

• AA, AA, aa, aa

• Aa, Aa, Aa, Aa

• AA, Aa, aa, aa

Answer explanation

Using a Punnett square for Aa x Aa, the combinations are: AA, Aa, Aa, and aa. This results in one homozygous dominant (AA), two heterozygous (Aa), and one homozygous recessive (aa), matching the correct choice: AA, Aa, Aa, aa.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

If a parent has a genotype of Bb and the other parent has a genotype of bb, what is the probability of their offspring having the genotype Bb?

• 0%

• 25%

• 50%

• 100%

Answer explanation

The Bb parent can pass either B or b (50% each), while the bb parent can only pass b. Thus, the possible genotypes for the offspring are Bb (50%) and bb (50%). Therefore, the probability of Bb is 50%.

Tags

NGSS.HS-LS3-3

Explain how a genotype of Aa can result in a dominant phenotype.

• The recessive allele is expressed

• The dominant allele is masked

• The dominant allele is expressed

• Both alleles are expressed equally

Answer explanation

In a genotype of Aa, the dominant allele (A) is expressed, leading to the dominant phenotype. The presence of the recessive allele (a) does not affect the expression of the dominant trait.

A plant with genotype Tt is crossed with another plant with genotype Tt. What is the probability of obtaining a plant with the recessive phenotype?

• 0%

• 25%

• 50%

• 75%

Answer explanation

In a Tt x Tt cross, the possible genotypes are TT, Tt, Tt, and tt. Only the tt genotype expresses the recessive phenotype. Thus, the probability of obtaining a plant with the recessive phenotype (tt) is 1 out of 4, or 25%.

Tags

NGSS.HS-LS4-3

Design a Punnett square to show the cross between a homozygous dominant individual (AA) and a heterozygous individual (Aa). What are the possible genotypes of the offspring?

• AA, Aa

• Aa, aa

• AA, aa

• Aa, Aa

Answer explanation

In a Punnett square for AA (homozygous dominant) and Aa (heterozygous), the possible genotypes of the offspring are AA and Aa. Thus, the correct answer is AA, Aa.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

If a child has a recessive trait, what can be inferred about the parents' genotypes?

• Both parents must be homozygous dominant

• At least one parent must be homozygous recessive

• Both parents must carry at least one recessive allele

• Both parents must be homozygous recessive

Answer explanation

If a child expresses a recessive trait, it indicates that they have two recessive alleles. Therefore, both parents must carry at least one recessive allele, making the correct choice: both parents must carry at least one recessive allele.

What is the phenotype ratio of offspring from a cross between two heterozygous individuals (Aa x Aa)?

• 1:2:1

• 3:1

• 1:1

• 2:2

Answer explanation

In a cross between two heterozygous individuals (Aa x Aa), the possible genotypes are AA, Aa, Aa, and aa. This results in a phenotype ratio of 3 dominant (A) to 1 recessive (a), hence the correct answer is 3:1.

In a hands-on activity using colored beads to represent alleles, red beads represent dominant alleles and blue beads represent recessive alleles. If a student picks one red bead and one blue bead, what is the genotype and phenotype?

• Genotype: BB, Phenotype: Recessive

• Genotype: Bb, Phenotype: Dominant

• Genotype: bb, Phenotype: Recessive

• Genotype: Bb, Phenotype: Recessive

Answer explanation

The student has one red bead (dominant allele) and one blue bead (recessive allele), resulting in the genotype Bb. Since the dominant allele is present, the phenotype is dominant.

Tags

NGSS.HS-LS3-1