1. The diagram below shows two processes (A and B) involved in sexual reproduction in plants and

animals.

Which statement best explains how these processes often produce offspring that have traits not

present in the parents?

(A) New traits are often observed in offspring because chromosomal nondisjunction often

occurs during process A, and this results in extra or missing genes in the offspring, which

results in new phenotypes.

Distractor Rationale:

This answer suggests the student may understand that nondisjunction can result in new

phenotypes due to extra or missing genes, but does not understand that this is a relatively

rare process and would not account for the commonly observed differences between

offspring and parents. The student may not understand the relationship between genes

and chromosomes, and therefore may not recognize that when homologous chromosomes

are separated during meiosis (process A) and then paired with new homologs during

fertilization (process B), new traits commonly appear in offspring without any change in the

number of genes in the offspring.

(B) New traits are often observed in offspring because homologous chromosomes are

separated during process A and then combined during process B, resulting in the

expression of recessive genes in the offspring.

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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Rationale:

This answer suggests the student understands that when homologous chromosomes are

separated during meiosis and then paired with new homologs during fertilization, new traits

can appear because of the combination of recessive genes in the offspring.

(C) New traits are often observed in offspring because crossing over occurs during process A,

and this results in genetic recombination, in which new genes are introduced into the

offspring during process B.

Distractor Rationale:

This answer suggests the student may understand that crossing over during meiosis can

result in new phenotypes because of gene recombination in chromosomes, but does not

understand that this would not introduce new genes because crossing over reflects the

rearrangement of parental genes on chromosomes, but not the introduction of new genes.

The student may not understand the relationship between genes and chromosomes, and

therefore may not recognize that when homologous chromosomes are separated during

meiosis (process A) and then paired with new homologs during fertilization (process B), new

traits commonly appear in offspring without any change in the number of genes in the

offspring.

(D) New traits are often observed in offspring because, directly following process B, many

chromosomes are inactivated, which prevents the expression of many parental genes and

results in new traits in the offspring.

Distractor Rationale:

This answer suggests the student may understand that during development, many genes

are not expressed in cells, but does not understand that this differential gene expression

occurs during all development and is not usually the cause of differences between parents

and offspring. The student may not understand the relationship between genes and

chromosomes, and therefore may not recognize that when homologous chromosomes are

separated during meiosis (process A) and then paired with new homologs during fertilization

(process B), new traits commonly appear in offspring without any change in the number or

expression of genes in the offspring.

Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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2. The diagram below shows the location of the BRCA1 allele, of which humans possess two

copies, one on each homologous pair of chromosome 17.

Carrying a harmful BRCA1 allele greatly increases the risk of breast and uterine cancer. If such

an allele is detected in a developing embryo, which prediction best explains its transmission to

future cells?

(A) The BRCA1 allele will be passed on to all body cells through mitotic divisions and will be

passed on to half of the sex cells during meiosis, because homologous chromosomes are

segregated during meiosis.

Rationale:

This answer suggests the student understands that, during mitosis, each daughter cell

receives a copy of each chromosome, and that, during meiosis, each sex cell receives one

chromosome of each homologous pair, which results in half of the sex cells receiving the

BRCA1 allele.

(B) The BRCA1 allele will be passed on to half of the body cells and one quarter of the sex cells,

because half of the daughter cells receive the allele during mitosis and one quarter of the

sex cells receive the cell during meiosis.

Distractor Rationale:

This answer suggests the student may understand that mitosis involves one division and

meiosis involves two divisions, but does not understand that all body cells and half of the

sex cells would receive the harmful BRCA1 allele because mitosis produces genetically

identical daughter cells, whereas meiosis produces haploid cells with only one of each

homologous pair.

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(C) The BRCA1 allele will be passed on to cells that develop into breast and uterine tissue

through mitotic divisions, but will not be passed on to sex cells, because sex cells are

derived from cells in the ovaries.

Distractor Rationale:

This answer suggests the student may understand that the BRCA1 allele will be passed on

to cells that develop into breast and uterine tissue, but does not understand that all other

cells will also contain the BRCA1 allele because mitosis produces genetically identical

daughter cells, and that, while all of the cells in the body will contain the BRCA1 allele, only

some of the cells will ever express the allele.

(D) The BRCA1 allele will be passed on to half of the body cells through mitotic divisions and

will be passed on to half of the sex cells during meiosis, because homologous chromosomes

are segregated during cell division.

Distractor Rationale:

This answer suggests the student may understand that half of the sex cells will receive the

harmful BRCA1 allele through meiosis, but does not understand that all of the body’s cells

would have the allele because mitosis produces genetically identical daughter cells.

Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype

3. The diagrams below show cells during stages of mitosis and meiosis.

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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Which statement best explains where variation is introduced into daughter cells?

(A) Variation is introduced at stage 1 and stage 2 of meiosis I, because during stage 1, crossing

over occurs, and during stage 2, chromosomes are randomly arranged in the middle of the

cell and independent assortment occurs.

Rationale:

This answer suggests the student understands that genetic variation is introduced into cells

during stages 1 and 2 of meiosis I, because during stage 1, crossing over occurs, and during

stage 2, independent assortment of homologous chromosomes occurs.

(B) Variation is introduced at stage 1 of mitosis and meiosis, because during stage 1 of mitosis

and meiosis, crossing over of homologous chromosomes occurs.

Distractor Rationale:

This answer suggests the student may understand that stage 1 of meiosis introduces

genetic variation into the cells because this is when crossing over occurs, but does not

understand that genetic variation is not introduced during stage 1 of mitosis because

crossing over does not normally occur during mitosis.

(C) Variation is introduced at stage 2 of mitosis and meiosis and stage 6 of meiosis, because

during these stages, homologous chromosomes are randomly arranged in the middle of the

cell and independent assortment occurs.

Distractor Rationale:

This answer suggests the student may understand that stage 2 of meiosis introduces

variation into cells because independent assortment of homologous chromosomes occurs,

but does not understand that stage 6 of meiosis separates sister chromatids, which does

not introduce variation because these chromosomes are identical except for any crossing

over that may have previously occurred, and that variation is introduced during meiosis, not

mitosis.

(D) Variation is introduced at stage 3 and stage 7 of meiosis, because during these stages,

different chromosomes are being separated into genetically unique daughter cells.

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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Distractor Rationale:

This answer suggests the student may understand that during stage 3 of meiosis and stage

7 of meiosis, chromosomes are separated, but does not understand that this separation of

chromosomes does not introduce genetic variation because variation is introduced during

crossing over, and that independent assortment occurs during meiosis, not mitosis.

Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype

4. The diagram below shows the karyotype of an insect (2n=10).

 

 

The reproductive organs of the insect are exposed to two chemicals that have the following

effects on cells:

DNA replication is prevented.•

Meiosis II is blocked.•

Which prediction explains how meiosis will most likely be altered in the insect’s sex cells when

its reproductive organs are exposed to the chemicals?

(A) The insect will produce four diploid sex cells that are genetically identical to the parent cell.

Distractor Rationale:

This answer suggests the student may understand that four cells are normally produced

after meiosis, but does not understand that if both DNA replication and meiosis II were

blocked, meiosis I would separate homologous chromosomes into only two genetically

unique haploid cells, because only separation of non-replicated, homologous chromosomes

would occur.

(B) The insect will produce four haploid sex cells that are genetically different from the parent

cell.

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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Distractor Rationale:

This answer suggests the student may understand that four cells are normally produced

after meiosis, and that the cells produced would be genetically unique from the parent cells,

but does not understand that if both DNA replication and meiosis II were blocked, meiosis I

would separate homologous chromosomes into only two genetically unique haploid cells,

because only separation of non-replicated, homologous chromosomes would occur.

(C) The insect will produce two diploid sex cells that are genetically identical to the parent cell.

Distractor Rationale:

This answer suggests the student may understand that diploid sex cells would be produced

if meiosis II were blocked, but does not understand that if both DNA replication and

meiosis II were blocked, meiosis I would separate homologous chromosomes into two

genetically unique haploid cells, because only separation of non-replicated, homologous

chromosomes would occur.

(D) The insect will produce two haploid sex cells that are genetically different from the parent

cell.

Rationale:

This answer suggests the student understands that if DNA replication and meiosis II were

blocked, meiosis I would separate homologous chromosomes into two genetically unique

haploid cells, because only separation of non-replicated, homologous chromosomes would

occur.

Aligned to: LO 3.24 CA 3.24: Predict Impact of Change in Genotype

3.24 B: Genetic Variation at the Chromosomal Level Quiz

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