Genetics Chapter 6

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1. 
Chromosome mutations are
 
variations in the number and structure of chromosomes and also play an important role in evolution
 
2. 
Variations in chromosomes may lose or gain
 
parts of induvidual chromosomes and the order of genes within a chromosome may become altered
 
3. 
Metacentric
 
The centromere is located approximately in the middle, and the chromosome has two arms of EQUAL length
 
4. 
Submetacentric
 
The centromere is displaced toward one end, creating a short and a long arm which is represented by p and q
 
5. 
Submetacentric arms
 
P arm: "petitie" arm
 
6. 
Acrocentric
 
The centromere is near one end, producing a long arm and a knob, or satelliite, at the other end
 
7. 
Telocentric
 
The centromere is at or very near the end of the chromosome
 
8. 
The compelete set of chromosomes possesed by an organism is called a
 
karyotype
 
9. 
To determine chromosome structure and viewing is best carried out by which cell stage
 
metaphase, where the chromosomes are lined up
 
10. 
A human karyotype consists of
 
46 chromosomes
 
11. 
Staining of chromosomes with a special dye called Giemsa reveals
 
G bands
 
12. 
G bands
 
distinguish areas of DNA that are rich in adenine-thymine (A-T) base pairs
 
13. 
Q bands are revealed by staining chromosomes
 
with quinacrine mustard and viewing chromosomes under ultraviolet light
 
14. 
Variation in the brightness if the Q bands results from
 
differences in the relative amounts of cytosine-guanine (C-G) and adenine-thymine base pairs
 
15. 
C band techniques
 
which are regions of DNA occupied by centromeric heterochromatin
 
16. 
R bands
 
are rich in cytocine-guanine base pairs
 
17. 
Chromosome mutations
 
1) chromosome rearrangement 2) aneuploids 3) polyploids
 
18. 
Chromosome rearrangements alter the structure
 
of chromosomes. For example: a piece of chromosome might be 1) duplicated 2) deleted 3) inverted
 
19. 
In aneuploidy the number of chromosomes
 
is altered: one or more individual chromosomes are added or deleted
 
20. 
in polyploidy
 
one or more complete sets of chromosomes are added.
 
21. 
Chromosome mutations consist of
 
chromosome 1) rearrangements 2) aneuploids 3) polyploids
 
22. 
Chromosome rearrangements are
 
mutations that change the structure of individual chromosomes.
 
23. 
Four basic chromosome rearrangements
 
1) duplications 2) deletions 3) inversions 4) translocations
 
24. 
Duplication
 
a segement of the chromosome is duplicated
 
25. 
Deletion
 
a segement of a chromosome is deleted
 
26. 
Inversion
 
a segement of the chromosome is turned 180 degrees
 
27. 
Translocation
 
a segement of chromosome moves from one chromosome to a nonhomlogous chromosome or to another place on the same chromosome
 
28. 
Chromosome duplications is
 
a mutationn in which part of the chromosome has been doubled
 
29. 
Chromosome duplication example
 
AB*CDEFG (EF segements) = AB*CDEFEFG
 
30. 
Tandem duplication
 
in which the duplicated region is IMMEDIATELY adjacent to the original segement
 
31. 
Displaced duplication
 
If the duplicated segment is located some distance from the original segment, either on the same chromosome or on a different one
 
32. 
Example of a displaced duplication
 
AB*CDEFG (EF segments) =AB*CDEFGEF
 
33. 
Reverse duplication (when the duplication is inverted)
 
a duplication can be either in the same orientation as that of the original sequence , as in the two preceeding examples or inverted
 
34. 
Example of a reverse duplication
 
AB*CDEFG (EF segments) =AB*CDEFFEG
 
35. 
In an individual heterozygous for a duplication
 
the duplicated chromosome loops out during pairing in prophase I
 
36. 
An individual homozygous for duplication carries the duplication on
 
both homologous chromosomes
 
37. 
An individual heterozygous for a duplication for a duplication has
 
one normal chromosome and one chromosome with the duplication
 
38. 
Duplications have major effects on
 
phenotype
 
39. 
The pairing and synapsis of homologous regions require that one or both
 
chromosomes loop and twist so that these regions are able ot line up
 
40. 
The amount of a particular protein
 
synthesized by a cell is often directly related to the number of copies of its corresponding gene
 
41. 
An individual organism eith three functional copies of a gene
 
often produces 1.5 times as much of the protein encoded by an individual with two copies
 
42. 
Proper gene dosage = critical
 
if the amount of one protein increases which the amounts of others remain constant, problems can result
 
43. 
Segemental duplication
 
defined as duplications greater than 1000 base pairs (1000 bp ) in length
 
44. 
Unequal crossing over produces
 
Bar and double-bar mutations
 
45. 
In chromosomes with Bar
 
1) unequal crossing over between chromosomes containing teo copies of bar...2) produces a chromosome with three Bar copies (double Bar mutation 3) and a wild-type chromosome
 
46. 
4 percent of the human genome consists
 
of segemental duplications
 
47. 
in the human genome,
 
the average size of segmental duplications is 15,000bp
 
48. 
Segmental duplication arise from processes that generate chromosome duplications
 
such as unequal crossing over
 
49. 
Crossing over between two duplicated sequences
 
located at different postions on a chromosome can generate additional duplications, deletions, and other chromosome rearrangements, which often result in genetic disorders through abnormal gene dosage
 
50. 
Over evolutionary time, segmental duplication often give rise to new genes while the original gene sequence continues to funtion,
 
the segmental duplication may undergo chnage and eventually provide a new function
 
51. 
A chromosome duplication is a mutation that doubles part of a chromosome. In individuals heterozygous for a chromosome duplication, the duplicated region of the chromosome loops out when homologous chromosomes pair in prophase I of meiosis. Duplications often have major effects on the phenotype, possibly by altering gene dosage. Segmental duplications are common within the human genome. Chromosome duplications often result in abnormal phenotypes because:
 
Developmental processes depend on the relative amounts of proteins encoded by different genes
 
52. 
Chromosome deletion
 
loss of a chromosome segment
 
53. 
Example of a chromosome deletion
 
AB*CDEFG ( deletion of EF segement) = AB*CDG
 
54. 
In individuals heterozygous for deletions, the normal chromosome
 
must loop out during the pairing of homologs in prophase I of meiosis to allow the homologous regions of the two chromosomes to align and undergo synapsis.
 
55. 
Effects of deletions
 
3 types
 
56. 
The heterozygous condition may produce imbalances
 
in the amounts of gene products similar to the imbalances produced by extra gene copies
 
57. 
Normally recessive mutations on the homologous chromosome lacking
 
the deletion may be expressed when the wild type allele has been deleted ( and no londer is present to mask the recessive allele's expression)
 
58. 
Pseudodominace
 
is the expression of a normally recessive mutation
 
59. 
Pseudodominance is an
 
indication that one of the homologous chromosome has a deletion
 
60. 
Some genes must be present in two copies for a normal function
 
When a single copy of a gene is not sufficient to produce a wild type phenotpe, it is said to be haploinsufficient gene
 
61. 
In an individual heterozygous for a deletion
 
the normal chromosome loops out during chromosome pairing in prophase I
 
62. 
When a single copy of a gene is not sufficient to produce a wild-type phenotype it is said to be
 
haploinsufficient gene
 
63. 
A chromosomal deletion is a mutation in which a part of a chormosome is lost. In individuals heterozygous for a deletion, the normal chromosomes loops out during Prophase I of meiosis. Deletions cause recessive genes on the homologous chromosome to be expressed and may cause imbalances in gene products.
 
Question: What is pseudodominance and how is it produced bt a chromosome deletion? ANSWER: Pseudodominance is the expression of a recessive mutation. It is produced when the dominant wild type allele in a heterozygous individual is absent due to a deletion on one chromosome
 
64. 
Effects of inversions
 
Individudal organsims with inversions have neither lost nor gained any genetic material: just the order of the chromosome segemetn has been altered.
 
65. 
An inversion my break a gene into two parts
 
with one part moving to a new location and the other destroying the function of that gene
 
66. 
Even when the chromosome breaks are between genes
 
phenotypic effects may arise from the inverted gene order in an inversion
 
67. 
Many genes are regualted in a position dependent manner and if their postions are altered by an inversion
 
they may be expressed at inappropriate times or in inappropriate tissues, therefore the outcome is referred to as a POSITION EFFECT
 
68. 
Homozygous for inversions
 
no special problems arise
 
69. 
Heterozygous for inversions
 
the gene order of the teo homologs differs and the homologous sequences can align and pair only if the two chromosomes form an inversion loop
 
70. 
Individuals heterozygous for inversions
 
also exhibit reduced recombination among genes located in the inverted region
 
71. 
The frequency of crossing over within the inversion is not actually diminished but
 
when crossing over does take place, the result is abnormal gametes that result are nonviable offspring and therefore no recombinant progeny take place
 
72. 
In an individual heterozygous for a paracentric inversion
 
the chromosomes form an inversion loop during pairing in prophase I
 
73. 
The heterozygote has one normal chromosome and one chromosome with an inverted segement
 
In prophase I of meiosis, the chromosomes form an inversion loop which allows the homologous sequences to align
 
74. 
The individual is heterozygous for an inversion with
 
one wild type unmutated chromosome (AB*CDEFG) and one inverted chromosome (AB*EDCFG)
 
75. 
In Prophase I of meiosis
 
an inversion loops forms, allowing the homologous sequences to pair up
 
76. 
If a single crossover takes place in the inverted region (between C and D) an unusual
 
structure results
 
77. 
The two outer chromatids, which do not participate in crossing over, contain
 
original, nonrecombinant gene sequences
 
78. 
The two inner chromatids, which did participate in crossing over
 
are highly abnormal: each has two copies of some genes and no copies of others
 
79. 
One of the four chromatids now has two centromeres and is said to be a
 
dicentric chromatid
 
80. 
Acentric chromatid
 
lacks a centromere
 
81. 
Anapahse I of meiosis
 
the centromeres are pulled toward opposite poles and the two homologous chromosomes seperate
 
82. 
This action stretches the dicentric
 
chromatid across the center of the nucleus, forming a sturcture called a DICENTRIC BRIDGE
 
83. 
Dicentric bridges eventually break as the
 
two centromeres are pulled futher apart
 
84. 
Spindle fibers do not attach to the acentric fragment and
 
so this fragment does not segregate to a spindle pole and is usually lost when the nucleus re-forms
 
85. 
In the second division of meiosis, the chromatids
 
seperate and four gametes are produced
 
86. 
Two of the gametes contain the original, nonrecombinant chromosomes (AB*CDEDG and AB*EDCFG)
 
and the other two gametes contain recombinant chromosomes that are missing genes therefore these gametes will not produce viable offspring
 
87. 
No recombinant progeny result when crossing over takes place within a paracentric-inversion
 
crossing over still takes place but when it does take place, the resulting recombinant gametes are not viable so no recombinant progeny are observed
 
88. 
In an individual heterozygous for a paracentric inversion
 
the chromosomes form an inversion loop during pairing in Prophase I
 
89. 
In a heterozygous individual
 
a single crossover within a paracentric inversion leads to abnormal genes
 
90. 
Steps and concepts
 
1) the heterozygote prossesses one wild type chromosome 2) and one chormosome with a paracentric inversion 3) in prophase 1 an inversion loop forms 4) a single crossover within the inverted region 5) results in an unusual structure 6) one of the four chromatids now has two centromeres 7) and one lacks a centromere 8) in anaphse 1 the centromeres separate, stretching the dicentric chromatid, which breaks. The chromosome lacking a centromere is lost. 9) two gametes contain non-recombinant chromosomes: one wild type (normal) and one with the inversion 10) The other two contain recombinant chromosomes that are missing some gene; these gametes will not produce viable offspring
 
91. 
Recombinant gametes are nonviable because
 
genes are either missing or present in too many copies
 
92. 
What happens?
 
1) The heterozygous possesses one wild type chromosome 2)and one chromosome with a pericentric inversion 3)In prophase I an inversion loop forms 4) if crossing over takes place within the inverted region 5) two of the resulting chromatids have too many copies of some genes and no copies of others 6) The chromosomes separate in anaphase I 7) The sister chromatids separate in anaphase II forming four gametes
 
93. 
Which results in....
 
-Normal nonrecombinant gametes -nonviable recombinant gametes - nonrecombinant gametes with pericentric inversion
 
94. 
Recombination is also reduced within a
 
pericentric inversion
 
95. 
No dicentric bridges or acentric fragments are produced but the
 
recombinant chromosomes have too many copies of some genes and no copies of others so gametes that recieve the recombinant chromosomes cannot produce progeny
 
96. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
97. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
98. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
99. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
100. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
101. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
102. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
103. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
104. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
105. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
106. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
107. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants


















 
108. 
Double crossovers in which both crossovers are on the same strands (two strand double crossover) result
 
in functional recombinants
















 
109. 
In an inversion, a segment of a chormosome is turned 180 degrees. Inversions cause breaks in some genes and may move others to new locations. In individuals heterozygous for a chromosome inversion, the homologous chromosomes form a loop in Prophase I of meiosis. When crossing over takes place within an inverted region, nonviable gametes are usually produced, resulting in a depression in observed recombination frequencies.

A dicentric chromosome is produced when crossing over takes place in an individual heterozygous for which type of chromosome rearrangement?
 
paracentric inversion
 
110. 
Translocation
 
involves the movement of genetic material between nonhomologous chromosomes or within the same chromosome
 
111. 
Nonreciprocal translocation
 
genetic material moves from on chromosome to another without any reciprocal exchange
 
112. 
Consider these two nonhomologous chromosomes: AB*CDEFG and MN*OPQRS
 
If chromosome segment EF moves from the first chromosome to the second without any transfer of segments from the second chromosome to the first, a nonreciprocal translocation has taken place producing AB*CDG and MN*OPEFQRS
 
113. 
reciprocal translocation
 
two way exchange between the chromosomes
 
114. 
A reciprocal translocation between chromosomes: AB*CDEFG and MN*OPQRS
 
=AB*CDQRG and MN*OPEFS
 
115. 
Translocations can phsyically link genes
 
that were formerly located on different chromosomes
 
116. 
These new linkage relations may affect gene expression ( postion effect)
 
genes translocated to new locations may come under the control of different regulatory sequences or other genes that affect their expression
 
117. 
The chromosomal breaks that bring about translocations
 
may take place within a gene and disrupt its function
 
118. 
Deletions accompany
 
translocations
 
119. 
Robertsonian translocation
 
the long arms of two acrocentric chromosomes become joined to a common (1) centromere through a translocation, generating a metacentric chromosome with two very short arms
 
120. 
The smaller chromosome fails to segregate leading to
 
an overall reduction in chromosome number
 
121. 
Robertsonian translocations are the causeof some cases of
 
Down syndrome
 
122. 
Individual heterozygous for a reciprocal translocation:
Original chromosomes: AB*CDEFG and M*NOPQRST and that a reciprocal translocation takes place
 
producing chromosomes AB*CDQRST and M*NOPEFG
 
123. 
Individual heterozygous for this translocation would possess
 
one normal copy of each chromosome and one translocated copy
 
124. 
Each of these chromosomes contains segments that are homologous to
 
two other chromosomes
 
125. 
When the homologous sequences pair in prophase I of meiosis
 
crosslike configurations consisting of all four chromosomes form
 
126. 
Whether viable or noviable gametes can be produced depends on how the
 
chromosomes in these crosslike connfigurations separate
 
127. 
Only about half of the gametes from an individual heterozygous for a reciprocal translocation
 
are expected to be functional and these individuals exhibit reduced fertility
 
128. 
In translocations, parts of chromosomes move to other non-homologous or to other regions of the same chromosome. translocations can affect the phenotype by causing genes to move to new locations, where they come under the influence of new regulatory sequences, or by breaking genes and disrupting their function.

What is the outcome of a Robertsonian translocation?
 
One large chromosome and one very small chromosome with two very short arms
 
129. 
Fragile sites
 
Chromosomes of cells grown in culture sometimes develop constrictions or gaps at particular locations
 
130. 
Fragile sites
 
are prone to breakage under certain conditions.
 
131. 
More than 100 fragile sites have been identified on
 
human chromosomes
 
132. 
Fragile X-syndrome
 
a disorder that inculdes intellectual disability
 
133. 
Fragile sites are chromosomal regions susceptible
 
to breakage under certian conditions
 
134. 
Methods that measure variations that they detect are called
 
copy-number variations
 
135. 
Copy-number variations include
 
duplications and deletions that range in length from thousands of base pairs to several million base pairs
 
136. 
Fragile sites are contrictions or gaps in chromosomes that are prone to
 
breakage under certian conditions
 
137. 
Variations in the number of copies of particular DNA sequences (copy-number variations) are surprisingly common in the
 
human genome
 
138. 
Aneuploidy is an increase or decrease
 
in the number of individual chromosomes
 
139. 
Chromosome mutations
 
include changes in the number of chormosomes
 
140. 
Variations in chromosome number can be classified into two basic types:
 
1) aneuploidy 2) polyploidy
 
141. 
Aneuploidy
 
is the change in the number of individual chromosomes
 
142. 
Polyploidy
 
is the change in the number of chromosome sets
 
143. 
Aneuploidy causes:
 
1) a chromosome may be lost in the course of mitosis or meiosis for example-its centromere is deleted. Loss of a centromere prevents the spindle fibers from attaching so the chromosome fails to move to the spindle pole and does not become incorporated into a nucleus after cell division. 2) the small chromosome generated by a Robertsonian translocation may be lost in mitosis or meiosis. 3) Aneuploids may arise through nondisjunction
 
144. 
Nonodisjunction
 
the faliure of homologous chromosomes or sister chromatids to seperate in meiosis or mitosis.
 
145. 
nondisjunction leads to
 
some gametes or cells that contain an extra chromosome and other gametes or cells that are mssing a chromosome
 
146. 
Four types of common aneuploid conditions in diploid indiviiduals:
 
1) nullisomy 2) monosomy 3) trisomy 4) tetrasomy
 
147. 
Nullisomy
 
is the loss of both members of a homologous pair of chromosome. Represented 2n-2, where n refers ti the haploid number of chromosomes. Thus among humans, who normally prossess 2n-46 chromosomes, a nullisomic zygote at 44 chromosomes
 
148. 
monosomy
 
is the loss of a single chromosome, represented as 2n-1. A human monosomic zygote has 45 chromosomes
 
149. 
Trisomy
 
is the gain of a single chromosome
 
150. 
Trisomy
 
is repesented as 2n+1. A human trisomic zygote has 47 chromosomes. The gain of a chormosome means that there are three homologus copies of one chromosome. Most cases of Down Syndrome result from Trisomy chromosome 21
 
151. 
Tetrasomy
 
is the gain of two homologus chromosomes
 
152. 
Tetrasomy is represented as 2n+2
 
A human tetrasomic zygote has 48 chromosomes. Tetrasomy is not the gain of any two extra chromosomes, but rather the gain of two homologous chromosomes so there will be four homologous copies of a particular chomosome
 
153. 
A human tetrasomic zygote has
 
48 chromosomes
 
154. 
Tetrasomy is not the gain of any two extra chromosomes
 
but rather the gain of two homologous chromosomes so tere will be four homologous copies of a particular chromosome
 
155. 
Aneuploidy affects the number of gene copies but
 
not their nucelotide sequences, the effects of aneuploidy are most likely due to abnormal gene dosage
 
156. 
Major execption of aneuploidy
 


relation between gene number and gene dosage pertains to the genes on the mammalian x-chromosomes.

 
157. 
X-chromosome inactivation in males females
 
ensures males and females recieve the same functional dosage for x-lonked genes
 
158. 
Aneuploidy, the loss or gain of one or more individual chromosomes, may arise from the loss of a chromosome subsequent to translocation or from nondisjunction in meiosis or mitosis. It disrupts gene dosage and often has severe phenotypic effects.

A diploid organism has 2n=36 chromosomes. How many chromosomes will be found in a trisomic member of this species?

 
Answer: 37
 
159. 


Aneuploids can be produced through nondisjunction

 
in meiosis I, meiosis II and mitosis
 
160. 
Sex-chromosomes aneuploids
 
most common aneuploidy seen in living humans
 
161. 

Turner syndrome and Klinefelter syndrome result from

 
aneuploidy of the sex chromosomes
 
162. 
Autosomal aneuploids
 
resulting in live births are less common than sex chromosome aneuploids in humans probably because there is no mechanism of dosage compensation for autosomal chromosomes
 
163. 
Down syndrome
 


-the most common autosomal aneuploidy in humans
-also called trisomy 21
-1 in700 births

 
164. 
Primary Down syndrome
 
92% of human births have 3 full copies of chormosome 21.
A conditon terrmed pimary dow syndrome
 
165. 
familial Down syndrome
 
-4% of people with down syndrome
-46 chromosomes
-extra copy of part of chromosome21 is attached to another chromosome through a translocation
 
166. 
Primary down syndrome
 
is caused by the presence of three copies of chromosome 21
 
167. 
The transloaction of chromosome 21 onto another
 
chromosome results in familial Down syndrome
 
168. 
Familial Down syndrome arises in offspring whose parents are carrise of chromosomes that have undergone a Robertsonian translocation
 
most commonly between chromosome 21 and chromosome 14: the long arm of 21 and the short arm of 14 exchange places
 
169. 
Transloaction carriers
 
persons with this translocation, do not have down syndrome.

Although, they possess only 45 chromosomes, their phenotypes are normal
 
170. 
Translocation carriers are at increased risk for producing children with down syndrome
 
1) a parent who is a carrier for a 14-21 translocation is normal
2)Gametogenesis produces gametes in these possible chromosome combinations
3) if a normal persn mates with a translocaton carrier
4) two thirds of their offsping will be healty and normal- even the translocation carriers
5) but one-third wll have down syndrome
6)other chromosoma combinaton result in aborted embryos
 
171. 
Trisomy 18 also known as Edward Syndrome
 
-1 in 8000 live births
 
172. 
Trisomy 13
 
-also known as Patau syndome
-1 in 15000
 
173. 
Many tumor cells have extra or missing chromosomes or both
 
some types are associated with specific chromosome mutations, including aneuploidy and chromosome rearrangements
 
174. 
In humans, sex chromosome aneuploids are more common than autosomal aneuploids. X-chromosome inactivation prevents problems of gene dosage for x linked genes. Down syndrome results from three functional copies of chromosome 21, either through trisomy (primary down syndrome) or a Robertsonian translocation (familial down syndrome)

Why are sex-chromosome aneuploids more common than autoploids in humans and other mammals?
 
Dosage compensation prevents the expression of additional copies of x-linked genes in mammals, and there is little info in the y chromosome, so the extra copies of the x chromosomes do not have major effects on development. In contrast, there is no mechanism of dosage compensation for autosomes, and so extra copies of autosomal genes are expressed, upsetting development and causing spontaneous abortion or aneuploid embryos
 
175. 
Polyploids include
 
1) triploids (3n) 2) tetraploids (4n) 3) pentaploids (5n) 4) or even higher numbers of chromosome sets
 
176. 
Polyploidy is common in plants and is a
 
major mechanism by which new plant species and from 70% to 80% of grasses are polyploids
 
177. 
Two major types of polyploidy
 
-autopolyploidy -allopoloploidy
 
178. 
Autopolyploidy
 
in which all chromosomes sets are from a single species
 
179. 
Allopolyploidy
 
in which chromosomes sets are from two or more species
 
180. 
Autoployploidy is due
 
to accidents of meiosis or mitosis that produce extra sets of chromosomes, all derived from a single species
 
181. 
nondisjunction of all chromosomes in mitosis in an early 2n embryos-doubles the chromosome number and
 
produces a autotetraploid (4n)
 
182. 
An autotriploid (3n) may arise when a nondisjunction in meiosis produces
 
a diploid gamete that then fuses with a normal haploid gamete to produce a triploid zygote
 
183. 
Triploids may arise from a cross between an autotetraploid that produces
 
2n gametes and a diploid that produces (1n) gametes
 
184. 
unbalanced gametes
 
random segregation with various numbers of chromosomes
 
185. 
Allopolyploidy aries from hybrization between two species
 
the resulting po,lyploid carries chromosome sets derived from two or more species
 
186. 
amphidiploid
 
the type of allopolyploid, consisting of two combined diploid genomes
 
187. 
Autopolyploidy can arise through
 
nondisjunction in mitosis or meiosis
 
188. 
Autopolyploidy through mitosis
 
1) Diploid (2n) early embryonic cell 2) replication 3) separation of sister chromatids 4)nondisjunction (no cell division) 5)autotetraploid (4n) cell
 
189. 
Autoployploidy through meiosis
 
1) Diploid (2n) cell 2) replication 3) nondisjunction 4) gametes both 2n 5) fertilization of 1n 6)zygotes are triploid (3n) that then fuses with a 1n gamete to produce an autotriploid
 
190. 
in meiosis of an autotriploid,
 
homologous chromosomes can pair or not pair in three ways
 
191. 
Species 1 has 2n=14 and species II has 2n=20. Give all the possible chromosomal numbers that may be found in the following indivudials
 
a) An autopolyploid of speceis I A: b) an autotetraploid of species II A: c) An allotriploid formed from species I and species II A: d) An allotetraploid formed from species I and species II A;
 
192. 
Polyploidy is the pressence of extra chromosome sets: autoployploidy possess extra chromosome sets fromt he same species; allopolyploids possesss extra chromosome sets from two or more species. Problems in chromosome pairing and segregation often lead to sterility in autopolyploids, but many allopolyploids are fertile.
 
Species A has 2n=16 chromosomes and species B has 2n=14. How many chromosomes would be found in an allotriplod of these two species? Answer: 22 or 23
 
193. 
Polyploidy, particularly allopolyploidy, often
 
gives rise to new species and has been particualy important in the evolution in flowering plants
 
194. 
Three basic types of chromosome mutations are:
 
1) chromosome rearrangements, which are changes in the structure of chromosomes 2)aneuploidy, which is an increase or decrease in chromosome number and 3) polyploidy, which is the presence of extra chromosome sets
 
195. 
Chromosome rearrangments include
 
1) duplications 2)deletions 3)inversions 4)translocations
 
196. 
In individuals heterozygous for a duplication, the duplicated region will form a loop when homologous chromosomes pair
 
in meiosis. Duplications often have pronounced effects on the phenotype owing to unbalanced gene dosage
 
197. 
Segmental duplications are common in
 
the human genome
 
198. 
In individuals heterozygous for a deletion, one of the
 
chromosomes will loop out during pairing in meiosis.
 
199. 
Deletions may cause recessive alleles
 
to be expressed
 
200. 
Pericentric inversions include
 
the centromere; paracentric inversions do not
 
201. 
In individuals heterozygous for an inversion
 
the homolgous chromosomes form inversion loops in meiosis, with reduced recombination taking place within the inverted region
 
202. 
In translocation heterozygotes
 
the chromosomes form crosslike structures in meiosis
 
203. 
Fragile sites are constrictions or gaps that appear at particular regions on the chromosomes of cells grown in culture and are prone to
 
breakage under certain conditions
 
204. 
Copy- number variations are
 
differences in the number of copies of DNA sequences and include duplications and deletions
 
205. 
These variants are common
 
in the human genome: some are associated with diseases and disorders
 
206. 
Nullisomy is the loss of
 
two homologus chromosomes
 
207. 
monosomy is the loss of
 
one homologous chromosomes
 
208. 
Trisomy is the
 
addition of one homologus chomosome
 
209. 
Tetrasomy is the addition of two homologous
 
chromosomes
 
210. 
Aneuploidy usually causes drastic phenotypic effects because
 
it leads to unbalanced gene dosage
 
211. 
Primary Down syndrome is caused by the presence of three full copies of chromosome 21, whereas familial Down syndrome is
 
caused by the presence of two normal copies of chromosome 21 and a third copy that is attached to another chromosome through a translocation
 
212. 
All the chromosomes in an autopolyploid derive from one species
 
chromosomes in an allopolyploid come from two or more species
 
213. 
Chromosome variations have played
 
an important role in the evolution of many groups of organisms