Understanding Genetic Inheritance Concepts

Which term describes the physical appearance of an organism resulting from its genetic makeup?

• Genotype

• Phenotype

• Allele

• Trait

Answer explanation

The term 'phenotype' refers to the observable physical characteristics of an organism, which are influenced by its genetic makeup. In contrast, 'genotype' describes the genetic constitution, while 'allele' and 'trait' refer to specific genes and features.

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NGSS.HS-LS1-1

What is the term for different forms of a gene found at the same place on a chromosome?

• Traits

• Alleles

• Genotypes

• Phenotypes

Answer explanation

The term for different forms of a gene at the same location on a chromosome is 'alleles'. Traits refer to characteristics, genotypes are the genetic makeup, and phenotypes are the observable traits.

Which of the following best describes a homozygous genotype?

• Two different alleles for a trait

• Two identical alleles for a trait

• A dominant and a recessive allele

• The physical expression of a gene

Answer explanation

A homozygous genotype consists of two identical alleles for a trait, meaning both inherited alleles from each parent are the same. This distinguishes it from heterozygous genotypes, which have different alleles.

What is a Punnett square used for?

• To measure the length of DNA

• To predict the probability of offspring genotypes

• To identify dominant alleles

• To describe physical traits

Answer explanation

A Punnett square is a tool used in genetics to predict the probability of different genotypes in offspring based on the alleles of the parents, making 'To predict the probability of offspring genotypes' the correct choice.

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NGSS.HS-LS3-3

Which term refers to an allele that is masked when a dominant allele is present?

• Codominant

• Recessive

• Heterozygous

• Incomplete

Answer explanation

The term that refers to an allele that is masked by a dominant allele is 'recessive'. Recessive alleles only express their traits when two copies are present, while dominant alleles overshadow them.

• 0%

• 25%

• 50%

• 75%

Answer explanation

When crossing two Tt plants, the possible genotypes are TT, Tt, Tt, and tt. Only the tt genotype results in short plants. Thus, the probability of getting a short offspring (tt) is 1 out of 4, or 25%.

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NGSS.HS-LS3-1

NGSS.HS-LS3-2

NGSS.HS-LS3-3

• Blue eyes

• Brown eyes

• Both blue and brown eyes

• Green eyes

Answer explanation

The genotype Bb means the person has one dominant allele (B) for brown eyes and one recessive allele (b) for blue eyes. Since brown is dominant, the phenotype of this person is brown eyes.

Tags

NGSS.HS-LS1-1

NGSS.HS-LS3-1

Which cross would produce a 9:3:3:1 phenotypic ratio in the offspring?

• Monohybrid cross

• Dihybrid cross

• Test cross

• Back cross

Answer explanation

A dihybrid cross involves two traits, leading to a 9:3:3:1 phenotypic ratio in the offspring. This ratio arises from the combination of dominant and recessive alleles for both traits, unlike monohybrid crosses which yield a 3:1 ratio.

• Codominance

• Incomplete dominance

• Dominant

• Recessive

Answer explanation

The offspring of a red-flowered plant (RR) and a white-flowered plant (WW) show pink flowers, indicating that neither allele is completely dominant. This is a classic example of incomplete dominance.

Which of the following best describes codominance?

• Both alleles are blended in the phenotype

• Only the dominant allele is expressed

• Both alleles are fully expressed in the phenotype

• Neither allele is expressed

Answer explanation

Codominance occurs when both alleles in a genotype are fully expressed in the phenotype, resulting in a phenotype that shows both traits distinctly, rather than blending them or expressing only one.