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