AP Biology : Understanding Dominant and Recessive Traits

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #11 : Understanding Dominant And Recessive Traits

Which of the following is an example of a haploid cell? 

Possible Answers:

Skin cell

Brain cell

Zygote

Sperm cell

Correct answer:

Sperm cell

Explanation:

A haploid cell is a cell that possesses only a single set of chromosomes (n=23) as opposed to the double set found in somatic cells (2n=46). The gametes (sperm and ova) in humans are examples of haploid cells. Also, the zygote is formed upon fusion of two gametes, and is thus diploid.    

Example Question #12 : Understanding Dominant And Recessive Traits

The mating of two varieties of a species is called __________.

Possible Answers:

true-breeding

a Mendelian cross

hybridization

cross-pollination

Correct answer:

hybridization

Explanation:

Hybridization is the mating of two varieties of a species to produce hybrids. A classic example would be crossing purple flowered pea plants and white flowered pea plants. The resulting offspring would all be genetic hybrids in this case though they may only display one color.   

Example Question #11 : Understanding Dominant And Recessive Traits

If A is a dominant allele conferring brown hair and a is the recessive allele conferring blonde hair, a heterozygote as what genotype?

Possible Answers:

Aa

Brown hair

Blonde hair

AA

Correct answer:

Aa

Explanation:

A genotype is the genetic makeup of alleles coding for a characteristic. In this example, a heterozygote has one recessive and one dominant allele, making the genotype Aa. The phenotype is the observable expression of the genotype. Since a heterozygote has one dominant allele and one recessive allele, the dominant allele is exhibited, thus the phenotype is brown hair.

Example Question #14 : Understanding Dominant And Recessive Traits

If B is a dominant allele conferring a purple flower and b is the recessive allele conferring a white flower, a homozygote recessive plant will have what phenotype?

Possible Answers:

Aa

White flowers

Purple flowers

aa

Correct answer:

White flowers

Explanation:

The phenotype is the observable characteristic of an individual. In this example, a homozygous recessive plant will have a white flower phenotype and a genotype of aa.

Example Question #15 : Understanding Dominant And Recessive Traits

Which of the following is not true about alleles?

Possible Answers:

Alleles are variations of the same gene

Alleles for the same characteristic are located at the same locus

Humans have four alleles for each characteristic

Alleles are responsible for different phenotypes

Correct answer:

Humans have four alleles for each characteristic

Explanation:

An allele is a genetic variant of a given trait. Alleles for the given trait within an individual are located at the same genetic locus. The resulting observable characteristic is called a phenotype. Humans are diploid organisms, meaning that they have two copies of each gene, where each copy may be the same or different alleles.

Example Question #16 : Understanding Dominant And Recessive Traits

Which one of the following scientists carried out experiments using pea plants to discover the fundamental principles of genetics?

Possible Answers:

James Watson

Francis Crick

Louis Pasteur

Gregor Mendel

Correct answer:

Gregor Mendel

Explanation:

Gregor Mendel carried out experiments using pea plants to discover the fundamental principles of genetics. Louis Pasteur was a microbiologist who is known for his work with vaccines and pasteurization. Both Francis Crick and James Watson are credited for their discovery of the structure of DNA.

Example Question #17 : Understanding Dominant And Recessive Traits

What does the principle of dominance in genetics state?

Possible Answers:

A recessive allele will be expressed instead of a dominant allele.

Some alleles are dominant and are expressed instead of the recessive allele.

The genotype for eye color is the same for all eye colors.

Crosses between parents with different traits are called hybrids.

Correct answer:

Some alleles are dominant and are expressed instead of the recessive allele.

Explanation:

The principle of dominance in genetics states that some alleles are dominant and are expressed instead of the recessive allele. Hybrids are crosses between parents with different traits, and genotypes for different eye colors are different.

Example Question #18 : Understanding Dominant And Recessive Traits

Of the following genotypes, which one is homozygous dominant?

Possible Answers:

Tt

tT

tt

TT

Correct answer:

TT

Explanation:

The correct code for homozygous dominant is TT. Homozygous means the "same alleles," and the dominant allele is a capital letter, which, in this case is "T."

Example Question #19 : Understanding Dominant And Recessive Traits

Of the following genotypes, which one is homozygous recessive?

Possible Answers:

TT

tT

tt

Tt

Correct answer:

tt

Explanation:

The correct code for homozygous recessive is tt. Homozygous means the "same alleles," and recessive, in this case, is "t."

Example Question #20 : Understanding Dominant And Recessive Traits

If a homozygous tall pea plant and a homozygous short pea plant are crossed. Which of the following is observed, assuming pea plant height exhibits complete dominance?

Possible Answers:

All the F1 are short

The offspring are of intermediate height

No hybrids are produced

The recessive trait is not observed

Correct answer:

The recessive trait is not observed

Explanation:

When a homozygous tall pea plant and a homozygous short pea plant are crossed, the next generation are all heterozygous and the dominant allele is expressed in all the plants, and the recessive trait seems to disappear. Since we are not told whether the tall or short allele is dominant, we cannot assume either.

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