Chapter 8 Flashcards
1
Q
What is genetic variation?
A
Genetic differences among members of the same species or between different species.
2
Q
What is allelic variation?
A
Genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene.
3
Q
What is a cytogeneticist?
A
A scientist who studies chromosomes under the microscope.
4
Q
How do you determine how normal chromosomes of a species will look like?
A
Examine the chromosomes from several members of the given species.
5
Q
Fruit flies have how many chromosomes?
A
8 (4 pairs)
6
Q
How many chromosomes ddoes corn have?
A
20 (10 pairs).
7
Q
Why is it useful to stain chromosomes?
A
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.
8
Q
How do cytogeneticists classify chromosomes?
A
Location in the centromere
size
banding patterns
9
Q
What is metacentric?
A
A chromosome with the centromere in the middle.
10
Q
What is submetacentric?
A
Describes a chromosome in which the centromere is slightly off center.
11
Q
What is acrocentric?
A
A chromosome with the centromere significantly off center, but not at the very end.
12
Q
What is telocentric?
A
Describes a chromosome with its centromere at one end.
13
Q
The short arm of chromsomes is designated with what?
A
The letter p
14
Q
The long arm of the chromosomes is designated with what?
A
the letter q
15
Q
In a karyotype, the chromosomes are arranged with _____ on top and _____ on bottom.
A
Short arms on top
long arms on bottom
16
Q
In a karyotype, how are chromosomes numbered?
A
The largest chromosome according to size, has the smallest number.
17
Q
What if chromosomes are about the same size?
A
They are treated with stains, to produce a banding pattern.
18
Q
What is G banding?
A
The chromosomal banding pattern that is observed when the chromosomes have been treated with the chemical dye giemsa.
19
Q
Darker stained regions are considered what?
A
More tightly compacted.
20
Q
In humans how many G bands can be distinguished?
A
300
21
Q
The left chromatid shows what, while the right chromatid shows what?
A
Left: the expected banding pattern during metaphase
Right: the expected banding pattern during prometaphase.
22
Q
Why is the banding pattern of eukaryotic chromosomes useful?
A
To distinguish chromosomes from each other.
To Detect changes in chromosome structure.
23
Q
A chromosome that is metacentric has its centromere
a. at the very tip
b. near one end, but not the very tip
c. near the middle
d. at two distinct locations.
A
c. near the middle
24
Q
Staining eukaryotic chromosomes is useful because it makes it possible to
a. distinguish chromosomes that are similar in size and centromeric locations.
b. identify changes inchromosome structure.
c. explore evolutionary relationships among different species.
d. all of the above.
A
d. all of the above.
25
Which changes alter the total amount of genetic material?
Deletions and duplications
26
What happens when a deletion occurs?
A segment of chromosomal material is missing.
| The affected chromosome is deficient in a significant amount of genetic material.
27
What is deficiency?
Condition in which a segment of chromosomal material is missing.
28
What is duplication?
A segment of DNA that is repeated more than once within a genome.
29
Generally, what are inversions and translocations?
Chromosomal rearrangements.
30
What is an inversion?
A change in the orientation of genetic material along a chromosome such that a segment is flipped in the reverse direction.
31
What is translocation?
1. when one segment of a chromosome breaks off and becomes attached to a different chromosome or to a different part of the same chromosome.
2. when a ribosome moves from one codon in an mRNA to the next codon.
32
What is a simple translocation?
When one piece of a chromosome becomes attached to a different chromosome.
33
What is a reciprocal translocation?
When two different chromosomes exchange pieces.
34
A change in chromosome structure that does not involve a change in the total amount of genetic material is?
a. deletion
b. duplication
c. inversion
d. non of the above.
c. inversion
35
Why would a deletion occur?
When a chromosome breaks in one or more places and a fragment of the chromosome is lost.
36
A normal chromosome breaks into how many pieces?
Two separate pieces.
37
What is a terminal deletion?
When a segment is lost from the end of a linear chromosome.
38
What is a interstitial deletion?
When an internal segment is lost from a linear chromosome.
39
How else can deletion occur?
When recombination takes place at incorrect locations between two homologous chromosomes.
40
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.
41
The consequences of deletion depend on what?
The size of the deletion.
| Whether it includes genes or portions of genes that are vital to the development of the organism.
42
When deletions have a phenotypic effect they are usually what?
Detrimental.
43
Are deletions or duplications less harmful?
Duplications.
44
What are repetitive sequences?
DNA sequences that are present in many copies in the genome.
45
How can duplication occur?
A misaligned crossover of sequences that are very similar on homologs.
46
What is a nonallelic homologous recombination?
Recombination that occurs at sites within chromosomes due to the occurrence of repetitive sequences.
47
What is the result of nonallelic homologous recombination?
One chromatid has a duplication, the other has a deletion.
48
What is a gene duplication?
An increase in the copy number of a gene. Can lead to the evolution of gene families.
49
What is the underlying cause of nonallelic homologous recombination?
The pairing of homologous sites that duplicated within the chromosomes, which causes misalignement.
50
The phenotypic consequences of duplication are correlated with what?
Size
51
Over the course of many generations, duplication can lead to what?
The formation of a gene family.
52
What is a gene family?
Two or more different genes within a single species that are homologous to each other because they were derived from the same ancestral gene.
53
When two or more genes are derived from a single anscestral gene, they are said to be what?
homologous
54
What are paralogs?
Homologous genes within a single species that constitute a gene family.
55
What is an example of a paralog?
Globin genes.
56
What is copy number variation (CNV)?
A type of structural variation in which a segment of DNA that is 1000 bp or more in length commonly exhibits copy number differences among members of the same species.
So it occurs at the population level.
57
What is segmental duplication?
A small segment of a chromosome that has a tandem duplication.
58
Reserachers estimate that what range of percent of genome may show CNV within a typical species of animal or plant?
0.1 -10%
59
Most CNV is what?
inherited and happened in the past.
60
The proliferation of transposable elements may increase what?
The copy number of DNA segments.
61
Does CNV have any phenotypic consequences?
No, but may be related to certain diseases
62
Duplication and deletion are associated with many types of what?
Cancers.
63
Who came up with comparative genomic hybridization (CGH)? When?
Anne Kallioniemi
Daniel Pinkel
Associates
1992
64
What is comparative genomic hybridization?
A hybridization technique to determine if cells have changes in chromosome structure, such as deletions or duplications.
65
How do you do comparative genomic hybridization?
treat cancer cells with gree fluorescent dye
Normal with red.
Denature with heat treatment.
Hybridization occurs.
Then examined under a microscope, to determine the intensities of green and red fluorescence. The ratio determines if there has been deletion or duplication.
66
Which of the following statements is correct?
a. if a deletion and a duplication are the same size, the deletion is more likely to be harmful.
b. if a deletion and a duplication are the same size, the duplication is more likely to be harmful.
c. if a deletion and a duplication are the same size, the likelihood of causing harm is the same.
d. a deletion is always harmful, whereas a duplication is always beneficial.
a. if a deletion and a duplication are the same size, the deletion is more likely to be harmful.
67
With regard to gene duplications, which of the following statements is/are correct?
a. gene duplications may be caused by nonallelic homologous recombination.
b. large gene duplications are more likely to be harmful than smaller ones.
c. Gene duplications are responsible for creating gene families that encode proteins with similar and specilaized functions.
d. all of the above.
d. all of the above.
68
Geneticists classify inversions according to what?
The location of the centromere.
69
What is a pericentric inversion?
An inversion in which the centromere is located within the inverted region of the chromosome
70
What is a paracentric inversion?
An inversion in which the centromere is found outside the inverted region.
71
The majority of inversions do not have what?
Phenotypic consequences.
72
When the phenotype of an individual is altered due to inversion it is usually based on what?
The boundaries of the inverted segment.
73
What is a position effect?
A change in phenotype that occurs when the position of a gene is changed from one chromosomal site to a different location.
74
What percent of humans carry inversions?
2%
75
What is an inversion heterozygote?
A diploid individual that carries one normal chromosome and a homologous chromosome with an inversion.
76
What is the underlying cause of gamete abnormality?
crossing over within the inverted region.
77
For a normal chromosome and inversion chromosome to synapse properly what must happen?
Inversion loop must form to permit the homologous genes on both chromosomes to align next to each other despite the inverted sequences.
78
What is a inversion loop?
The loop structure that is formed when the homologous chromosomes of an inversion heterozygote attempt to align themselves during meiosis.
79
The consequences of an inverted chromosome crossover depends on what?
Whether the inversion is pericentric or paracentric.
80
What is the outcome if one of the homologs has a pericentric inversion?
Two abnormal chromosomes with deletion and duplication.
| May not be survivable or may cause phenotypic abnormalities.
81
What is the outcome if one of the homologs has a paracentric inversion?
One product is an acentric fragment
The other is a dicentric chromosome with a dicentric bridge.
Resulting in one chromosome with an inversion, one normal chromosome, and two chromosomes with deletions.
82
What is a acentric fragment?
A fragment of a chromosome that lacks a centromere.
83
What is a dicentric chromosome?
A chromosome with two centromeres.
84
What is a dicentric bridge?
The region between the two centromeres in a dicentric chromosome.
85
What usually prevents translocation from occuring in eukaryotic chromosomes?
Telomeres.
86
What are telomeres?
Specialized DNA sequences found at the linear eukaryotic chromosomes.
87
Telomeres allow what?
Cells to identify where a chromosome ends and prevent the attachment of chromosomal DNA to the natural ends of a chromosome.
88
When are cell ends considered reactive?
When exposed to an agent that causes chromosomes to break and the ends lack telomeres.
89
A reactive end readily binds to what?
Another reactive end.
90
What might cause reciprocal translocation to occur?
If multiple chromosomes are borken, the reactive ends may be joined incorrectly to produce an abnormal chromosome.
91
What is another way reciprocal translocation may occur?
when two nonhomologous chromosomes cross over.
92
Which of the two ways to cause translocation might be promoted by the presence of the same transposable element in many places in a species genome?
The pairing of nonhomologous chromosomes.
93
Reciprocal translocations are also called what?
Balanced translocations.
94
What are balanced translocations?
Translocation, such as a reciprocal translocation, in which the total amount of genetic material is normal or nearly normal.
95
Why are they called balanced translocations?
Because the total amount of genetic material is not altered.
96
Translocations usually occur with no what?
Phenotypic consequences.
97
Carriers of a balanced translocation are at risk of having offspring with what?
unbalanced translocation.
98
What is unbalanced translocation?
A translocation in which a cell has too much genetic material compared with a normal cell.
99
What is robertsonian translocation?
The structure produced when two telocentric chromosomes fuse at their short arms.
100
Robertsonian translocations involve only what?
Acrocentric chromosomes 13, 14, 15, 21, 22
101
Whether or not gametes are produced with unbalanced combination of chromosomes depends on what?
The segregation pattern during meiosis I.
102
What is a translocation cross?
The structure that is formed when the chromosomes of a reciprocal translocation attempt to synapse during meiosis. This structure contains two normal nontranslocated chromosomes and two translocated chromosomes. A total of eight chromatids are found within the cross.
103
Explain why these chromosomes form a translocation cross during prophase of meiosis I.
Because homologous regions are pairing with each other.
104
The expected segregation pattern is governed by what?
The centromeres.
105
What are the two segregation patterns seen for translocation?
Alternate segregation: the chromosomes separate diagonally. Adjacent-1 segregation: Adjacent chromosomes sort into the same cell.
106
What is the rare adjacent-2 segregation pattern?
The centromeres do not segregate. Both cells have copies of both the centromeres
107
What is semisterility?
when an individual has a lowered fertility.
108
What causes semisterility?
Adjacent-1 segregation
109
A paracentric inversion
a. includes the centromere within the inverted region.
b. does not include the centromere within the inverted region.
c. has two adjacent inverted regions.
d. has an inverted region at the very end of a chromosome.
b. does not include the centromere within the inverted region.
110
Due to crossing over within an inversion loop, a heterozygote within a pericentric inversion may produce gametes that
a. carry a deletion
b. carry a duplication
c. carry a translocation
d. include a and b
d. include a and b
111
A mechanism that may cause a translocation is
a. the joining of reactive ends when two different chromosomes break.
b. crossing over between nonhomologous chromosomes.
c. crossin gover between homologous chromosomes.
d. both a and b.
d. both a and b.
112
Variation in chromosome number can be categorized in what two ways?
Variation in the number of sets of chromosomes.
| Variation in the number of particular chromosomes within a set.
113
What are euploid?
An organism in which the chromosome number is an exact multipleof a chromosome set.
114
What is a triploid?
An organism or cell that contains three sets of chromosomes.
115
What is a tetraploid?
Having four sets of chromosomes.
116
What is a polyploid?
An organism or cell with three or more sets of chromosomes.
117
What is used to represent the sets of chromosomes?
N
| Example 2 sets of chromosomes= 2n
118
What is aneuploidy?
not euploid. Refers to a variation in chromosome number such that the total number of chromosomes is not an exact multiple of a set or n number.
119
What is trisomic?
a diploid cell with one extra chromosome. 2n + 1
120
What is monosomic?
A diploid cell that is missing a chromosome.
| 2n-1
121
Humans have 23 chromosomes per set. A person with 45 chromosomes could be described as being
a. euploid
b. aneuploid.
c. monoploid.
d. trisomic.
b. aneuploid.
122
Describe the imbalance in gene products that would occur in monosomy 2.
The genes on chromsome 2 would be found in single copies, whereas the genes on 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.
123
Are phenotypic effects caused by aneuploidy or monoploy?
Yes.
124
What percent of fertilized human eggs results in an embryo with an abnormality in chromosome number?
5-10%
125
50% of all spontaneous abortions are due to what?
Alterations in chromosome number
126
Which chromosome is nonlethal with the variation in the number of chromosomes?
X chromosome.
127
Older parents are more likely to produce children with what?
Abnormalities in chromosome number.
128
What is a reason for the relationship with maternal age and down syndrome?
Due to the age of the oocytes. Primary oocytes have been in prophase I for a progressively longer period of time. This added length of time may contribute to an increased frequency of nondisjunction.
129
In a trisomic individual, such as a person with trisomy 21 (down syndrome), a genetic imbalance occurs because.
a. genes on chromosome 21 are overexpressed.
b. genes of chromosome 21 are underexpressed .
c. genes on the other chromosomes are overexpressed.
d. genes on the other chromosomes are underexpressed.
a. genes on chromosome 21 are overexpressed.
130
Humans that survive with aneuploidy usually have incorrect numbers of chromosome 13, 18, or 21 or the sex chromosomes. a possible explanation why these abnormalities permit survival is because
a. the chromosomes have clusters of genes that aid in embryonic growth.
b. the chromosomes are small and carry relatively few genes.
c. X-chromosome inactivation.
d. both b and c.
d. both b and c.
131
What is variation in euploidy?
Changes in the number of sets of chromosomes.
132
Polyploidy in mammals is usually what?
A lethal condition.
133
Can euploidy occur ofter fertilization?
Yes.
134
In many animals, certain tissues of the body display what?
Normal variations in the number of sets of chromosomes.
135
What is an example of cells that are triploid, tetraploid or octaploid?
Human liver cells.
136
What is endopolyploidy?
In a diploid individual, the phenomenon in which certain cells of the boy may be polyploid.
137
What is the significance of endopolyploidy?
The increase in chromosome number in certain cells may enhance their ability to produce specific gene products that are needed in great abundance.
138
What are polytene chromosomes?
Chromosomes that are found in certain cells, such as Drosphila salivary cells, in which the chromosomes have replicated many times and the copies lie side by side.
139
What is the chromocenter?
The central point where polytene chromosomes aggregate.
140
Approximately how many copies of chromosome 2 are found in a polytene chromosome?
About 512
141
Plants more commonly exhibit what?
polyploidy
142
Among see and fern plants what percent are polyploid?
30-35%
143
Wheat is what?
a Hexaploid
144
strawberries can be what?
diploid
tetraploid
hexaploid
octaploid
145
A polyploid plant individual is usually what?
Larger
| More robust
146
Tetraploidy in animals may have what effect?
Little effect or be detrimental
147
What are some common advantages of polyploidy in plants?
More vigorous and disease resistant.
Larger flowers and produce more fruit.
Greater adaptability and can withstand harsher environmental conditions.
148
Odd number polyploids usually cannot what?
Reproduce.
149
Why are plants sterile if they have an odd number of polyploids?
They produce highly aneuploid gametes.
During prophase of meiosis I, homologous pairs of sister chromatids form bivalents. However odd number chromosomes display unequal separation of homologous chromosomes during anaphase of meiosis I.
The odd numbers cannot be divided eequally between daughter cells.
150
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.
151
When is sterility desired in agriculture?
For seedless fruit like bananas.
152
The term endopolyploidy refers to the phenomenon of having
a. too many chromosomes
b. extra chromosomes inside the cell nucleus.
c. certain cells of the body with extra sets of chromosomes.
d. extra sets of chromosomes in gamets.
c. certain cells of the body with extra sets of chromosomes.
153
In agriculture, an advantage of triploid plants is that they are
a. more fertile
b. often seedless.
c. always disease-resistant
d. all of the above.
b. often seedless.
154
What is nondisjunction?
An event in which the chromosomes do not segregate properly.
155
Meiotic nondisjunction is what?
The event in which chromosomes do not segregate equally during meiosis.
156
What is the result of meiotic nondisjunction?
Abnormal chromosome number in all cells.
157
What is mitotic nondisjunction?
An event in which chromosomes do not segregate equally during mitosis.
158
What is the result of mitotic nondisjunction?
May lead to a patch of tissue in the organism that has an altered chromosome number.
159
Nondisjunction can occur during what phase of meiosis I or II?
Anaphase
160
If nondisjunction occurs during meiosis I, what happens?
An entire bivalent migrates to one pole. so the four haploid cells will be abnormal.
161
If nondisjuntion occurs during meiosis II, what happens?
The net result is two abnormal and two normal haploid cells.
162
If a gamete from nondisjuntion during meiosis II, unites with a normal gamete, the offspring will be what?
Trisomic.
163
If a gamete missing a chromosome participates in fertilization, the offspring is what?
monosomic
164
Explain what the word nondisjunction means?
Pairs of chromosomes are not separating from each other properly.
