Ch. 8 Concept Check & Comprehensive Questions

Question 1

A chromosome that is metacentric has its centromere..

Answer 1

Near the middle

Question 2

Staining eukaryotic chromosomes is useful because it makes it possible to..

Answer 2

All of the above

• distinguish chromosomes that are similar in size and centromeric locations
• identify changes in chromosome structure
• explore evolutionary relationships among different species

Question 3

A change in chromosome structure that does not involve a change in the total amount of genetic material is..

Answer 3

An inversion

Question 4

Which of the following statements is correct?

Answer 4

If a deletion and a duplication are the same size, the deletion is more likely to be harmful

Question 5

With regard to gene duplications, which of the following statements is/are correct?

Answer 5

All are correct

• gene duplications may be caused by nonallelic homologous recombination
• large gene duplications are more likely to be harmful than smaller ones
• gene duplications are responsible for creating gene families that encode proteins with similar and specialized functions

Question 6

A paracentric inversion..

Answer 6

Does not include the centromere within the inverted region

Question 7

Due to crossing over within loop, a heterozygote with a pericentric inversion may produce gametes that..

Answer 7

• carry a deletion

- carry a duplication

Question 8

A mechanism that may cause a translocation is..

Answer 8

• the joining of reactive ends when two different chromosomes break
• crossing over between nonhomologous chromosomes

Question 9

Humans have 23 chromosomes per set. A person with 45 chromosomes could be described as being..

Answer 9

Aneuploid

Question 10

In a trisomic individual, such as a person with trisomy 21 (down syndrome), a genetic imbalance occurs because..

Answer 10

Genes on chromosome 21 are over expressed

Question 11

Humans that survive with aneuploidy usually have incorrect numbers of chromosome 13, 18, or 21 or the sex chromosomes. A possible expiation why these abnormalities permit survival is because..

Answer 11

• the chromosomes are small and carry relatively few genes

- x-chromosome inactivation

Question 12

The term endopolyploidy refers to the phenomenon of having..

Answer 12

Certain cells of the body with extra sets of chromosomes

Question 13

In agriculture, an advantage of triploid plants is that they are..

Answer 13

Often seedless

Question 14

In a diploid species, complete nondisjunction during meiosis I may produce a viable cell that is ___.

Answer 14

Diploid

Question 15

The somatic cells of an allotetraploid usually contain..

Answer 15

Two sets of chromosomes from two different species

Question 16

Features of normal chromosomes.

Why is it useful to stain chromosomes?

Answer 16

The staining of chromosomes results in banding patterns that make it easier to distinguish chromosomes that are similar in size and have similar centromere locations.

Question 17

Types of changes in chromosome structure

Which of these changes alter the total amount of genetic material?

Answer 17

Deletions and duplications alter the total amount of genetic material.

Question 18

Production of terminal and interstitial deletions.

Why is a chromosomal fragment without a centromere lost and then subsequently degraded?

Answer 18

If a chromosomal fragment does not contain a centromere, it will not segregate properly. If it remains outside the nucleus, it will be degraded.

Question 19

Nonallelic homologous recombination, leading to a duplication and a deletion.

What is the underlying cause of nonallelic homologous recombination?

Answer 19

Nonallelic homologous recombination occurs because of the pairing of homologous sites that duplicated within the chromosomes. This pairing causes the chromosomes to be misaligned.

Question 20

The consequences of crossing over in the inversion loop.

Explain why these chromosomes can synapse only if an inversion loop forms.

Answer 20

These chromosomes form an inversion loop because the homologous regions are pairing with each other. For the inverted and noninverted regions to pair, a loop must form.

Question 21

Two mechanisms that cause a reciprocal translocation.

Which of these two mechanisms might be promoted by the presence of the same transposable element in many places in a species genome?

Answer 21

The mechanism shown in part (b) may occur if transposable elements are found in different chromosomes. These elements may promote the pairing between nonhomologous chromosomes and a subsequent crossover could occur.

Question 22

Transmission of familial Down syndrome.

If these segregation patterns are equally likely, what is the probability that a gamete made from this individual will result in a viable offspring with a normal phenotype?

Answer 22

Two out of six gametes will produce a viable offspring with a normal phenotype. Therefore, the probability is 2/6, or 1/3.

Question 23

Meiotic segregation of a reciprocal translocation.

Explain why these chromosomes form a translocation cross during prophase of meiosis I.

Answer 23

These chromosomes form a translocation cross because homologous regions are paring with each other.

Question 24

Types of variation in chromosome number.

What adjectives can be used to describe a fruit fly that has a total of seven chromosomes because it is missing one copy of chromosome 3?

Answer 24

Aneuploid, monosomic, monosomy 3

Question 25

Imbalance of gene products in trisomic and monosomic individuals.

Describe the imbalance in gene products that would occur in monosomy 2.

Answer 25

The genes on chromosome 2 would be found in single copies, whereas the genes on the other chromosomes would be found in two copies. The expression of genes on chromosome 2 would be less relative to a normal individual. This creates an imbalance between genes on chromosome 2 and those on the other chromosomes.

Question 26

Polytene chromosomes in Drosophila.

Approximately how many copies of chromosome 2 are found in a polytene chromosome?

Answer 26

About 512

Question 27

Example of a polyploid plant.

What are some common advantages of polyploidy in plants?

Answer 27

They are often more vigorous and disease resistant. They may have larger flowers and produce more fruit.

Question 28

Schematic representation of anaphase of meiosis I in a triploid organism containing three sets of four chromosomes.

Explain why a triploid individual is usually infertile.

Answer 28

During meiosis in a triploid individual, the homologs cannot pair properly. This results in highly aneuploid gametes, which are usually nonviable. Also, if aneuploid gametes participate in fertilization, the offspring are usually nonviable.

Question 29

Nondisjunction during meiosis I and II.

Explain what the word nondisjunction means.

Answer 29

In this case, nondisjunction means that pairs of chromosomes are not separating from each other properly.

Question 30

What is the key difference between autopolyploidy and allopolyploidy?

Answer 30

In autopolyploidy, multiple sets of chromosomes come from the same species.

In allopolyploidy, multiple sets of chromosomes come from at least two different species.