High School Biology : Cell Biology

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #3 : Understanding Stages Of Meiosis

Sister chromatids separate in which stage of meiosis?                   

Possible Answers:

Anaphase I

Telophase I

Anaphase II

Telophase II

Correct answer:

Anaphase II

Explanation:

Chromatid disjunction occurs in anaphase II after the chromosomes line up along the equator during metaphase II. The chromosomes are then pulled apart, with one chromatid moving north, and one moving south. The next steps are telophase, and cytokinesis, which upon completion, will result in genetically distinct haploid gametes.

Example Question #11 : Meiosis

What is the final stage of meiosis? 

Possible Answers:

Anaphase II

Telophase II

Prophase II

Metaphase II

Correct answer:

Telophase II

Explanation:

Telophase is the final stage of both meiosis I and meiosis II. So telophase II is the final step of the overall process of meiosis. In telophase II, the daughter cells begin to form, the DNA begins to decondense, the nuclear membrane reforms, and the spindle apparatus breaks down. Cytokinesis is the physical splitting of the cell that follows mitosis/meiosis.   

Example Question #12 : Meiosis

During which phase of meiosis does chromosomal disjunction occur? 

Possible Answers:

Telophase I

Anaphase I

Metaphase I

Cytokinesis

Correct answer:

Anaphase I

Explanation:

Chromosome disjunction is the splitting up of paired of chromosomes. This occurs in anaphase I and anaphase II where the homologous chromosomes split and the sister chromatids split, respectively. Note that improper disjunction (nondisjunction) can be detrimental to the cell.

Example Question #12 : Meiosis

Which of the following best describes the reason for the genetic diversity of gametes?

Possible Answers:

None of these

All of these

Independent assortment

Crossing Over 

Correct answer:

Crossing Over 

Explanation:

Crossing over is the process in Meiosis I in which homologs line up on the metaphase plate and exchange genetic information, which changes the genetic make up of chromosomes. Independent assortment is a principle proposed by Gregory Mendel stating that genes assort independently during gamete formation, which creates genetic diversity. 

Example Question #1 : Understanding Crossing Over

Crossing over occurs during which stage of meiosis?

Possible Answers:

Prophase I

Anaphase I

Prophase II

Metaphase I

Correct answer:

Prophase I

Explanation:

During prophase I homologous chromosomes will line up with one another, forming tetrads. During this lining up, DNA sequences can be exchanged between the homologous chromosomes. This type of genetic recombination is called crossing over, and allows the daughter cells of meiosis to be genetically unique from one another.

Crossing over can only occur between homologous chromosomes. Cells become haploid after meiosis I, and can no longer perform crossing over.

Example Question #2 : Understanding Crossing Over

What is the evolutionary purpose of cells that undergo crossing over?

Possible Answers:

To produce two cells instead of one

To keep mutations from forming

To keep the redundancy of the cell high

To increase genetic diversity

To produce gametes that are genetically identical

Correct answer:

To increase genetic diversity

Explanation:

Crossing over is a process that happens between homologous chromosomes in order to increase genetic diversity. During crossing over, part of one chromosome is exchanged with another. The result is a hybrid chromosome with a unique pattern of genetic material. Gametes gain the ability to be genetically different from their neighboring gametes after crossing over occurs. This allows for genetic diversity, which will help cells participate in survival of the fittest and evolution.

Example Question #3 : Understanding Crossing Over

During which step of cell division does crossing over occur?

Possible Answers:

Prophase I

Metaphase I

Prophase II

Metaphase II

Correct answer:

Prophase I

Explanation:

When chromatids "cross over," homologous chromosomes trade pieces of genetic material, resulting in novel combinations of alleles, though the same genes are still present. Crossing over occurs during prophase I of meiosis before tetrads are aligned along the equator in metaphase I.

By meiosis II, only sister chromatids remain and homologous chromosomes have been moved to separate cells. Recall that the point of crossing over is to increase genetic diversity. If crossing over did not occur until sometime during meiosis II, sister chromatids, which are identical, would be exchanging alleles. Since these chromatids are identical, this swap of material would not actually change the alleles of the chromatids.

Example Question #4 : Understanding Crossing Over

What structures exchange genetic material during crossing over?

Possible Answers:

Non-homologous chromosomes

Egg and sperm chromosomes

Sister chromatids

Nonsister chromatids

Correct answer:

Nonsister chromatids

Explanation:

During crossing over, homologous chromosomes come together in order to form a tetrad. This close contact allows the nonsister chromatids from homolgous chromosomes to attach to one another and exchange nucleotide sequences. The word "nonsister" implies that the chromatids have the same genes, but are not exact copies of one another, as they come from separate chromosomes.

Example Question #3 : Understanding Crossing Over

Crossover of homologous chromosomes in meiosis occurs during which phase?

Possible Answers:

Prophase II of meiosis

Prophase I of meiosis

Anaphase II of meiosis

Anaphase I of meiosis

Correct answer:

Prophase I of meiosis

Explanation:

The crossing over of homologous chromosomes occurs in prophase I of meiosis. Prophase I of meiosis is characterized by the lining up of homologous chromosomes close together to form a structure known as a tetrad. A tetrad is composed of four chromatids.

Anaphase I is marked by the separation of homologous chromosomes, whereas in anaphase II there is the separation of sister chromatids. In anaphase I sister chromatids are still intact and connected at the centromere. Prophase II is similar to prophase in mitosis in that there is the break down of the nuclear membrane and the formation of spindle fibers in preparation for the separation of sister chromatids.

Example Question #4 : Understanding Crossing Over

During crossing over, two homologous chromosomes pair to form which of the following choices?

Possible Answers:

Mitotic Bond

None of these

Base Pair

Chromatid

Tetrad

Correct answer:

Tetrad

Explanation:

The tetrad, which divides into non-sister chromatids, exchanges genetic information in order to make the genetic pool more variant, and result in combinations of phenotypic traits that can occur outside of linked genotypic coding.

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