Ch. 8 Concept Check & Comprehensive Questions Flashcards
A chromosome that is metacentric has its centromere..
Near the middle
Staining eukaryotic chromosomes is useful because it makes it possible to..
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
A change in chromosome structure that does not involve a change in the total amount of genetic material is..
An inversion
Which of the following statements is correct?
If a deletion and a duplication are the same size, the deletion is more likely to be harmful
With regard to gene duplications, which of the following statements is/are correct?
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
A paracentric inversion..
Does not include the centromere within the inverted region
Due to crossing over within loop, a heterozygote with a pericentric inversion may produce gametes that..
- carry a deletion
- carry a duplication
A mechanism that may cause a translocation is..
- the joining of reactive ends when two different chromosomes break
- crossing over between nonhomologous chromosomes
Humans have 23 chromosomes per set. A person with 45 chromosomes could be described as being..
Aneuploid
In a trisomic individual, such as a person with trisomy 21 (down syndrome), a genetic imbalance occurs because..
Genes on chromosome 21 are over expressed
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..
- the chromosomes are small and carry relatively few genes
- x-chromosome inactivation
The term endopolyploidy refers to the phenomenon of having..
Certain cells of the body with extra sets of chromosomes
In agriculture, an advantage of triploid plants is that they are..
Often seedless
In a diploid species, complete nondisjunction during meiosis I may produce a viable cell that is ___.
Diploid
The somatic cells of an allotetraploid usually contain..
Two sets of chromosomes from two different species
Features of normal chromosomes.
Why is it useful to stain chromosomes?
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.
Types of changes in chromosome structure
Which of these changes alter the total amount of genetic material?
Deletions and duplications alter the total amount of genetic material.
Production of terminal and interstitial deletions.
Why is a chromosomal fragment without a centromere lost and then subsequently degraded?
If a chromosomal fragment does not contain a centromere, it will not segregate properly. If it remains outside the nucleus, it will be degraded.
Nonallelic homologous recombination, leading to a duplication and a deletion.
What is the underlying cause of nonallelic homologous recombination?
Nonallelic homologous recombination occurs because of the pairing of homologous sites that duplicated within the chromosomes. This pairing causes the chromosomes to be misaligned.
The consequences of crossing over in the inversion loop.
Explain why these chromosomes can synapse only if an inversion loop forms.
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.
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?
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.
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?
Two out of six gametes will produce a viable offspring with a normal phenotype. Therefore, the probability is 2/6, or 1/3.
Meiotic segregation of a reciprocal translocation.
Explain why these chromosomes form a translocation cross during prophase of meiosis I.
These chromosomes form a translocation cross because homologous regions are paring with each other.
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?
Aneuploid, monosomic, monosomy 3
Imbalance of gene products in trisomic and monosomic individuals.
Describe the imbalance in gene products that would occur in monosomy 2.
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.
Polytene chromosomes in Drosophila.
Approximately how many copies of chromosome 2 are found in a polytene chromosome?
About 512
Example of a polyploid plant.
What are some common advantages of polyploidy in plants?
They are often more vigorous and disease resistant. They may have larger flowers and produce more fruit.
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.
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.
Nondisjunction during meiosis I and II.
Explain what the word nondisjunction means.
In this case, nondisjunction means that pairs of chromosomes are not separating from each other properly.
What is the key difference between autopolyploidy and allopolyploidy?
In autopolyploidy, multiple sets of chromosomes come from the same species.
In allopolyploidy, multiple sets of chromosomes come from at least two different species.
