Chapter 6 Flashcards
1
Q
karyotype
A
- display of a complete set of chromosomes
2
Q
Chromosomal mutation Types
A
- chromosomal rearrangements
- aneuploids
- euploids (polyploidy)
3
Q
Aneuploids
A
- the number of chromosomes is altered (addition/deletion)
4
Q
euploids/polyploids
A
- one or more complete sets of chromosomes are added
5
Q
Tandem duplication
A
- duplicated region is immediately adjacent(next to)
6
Q
displaced duplication
A
- located a distance away (even on another chromosome)
7
Q
What is a characteristic of duplication?
A
- loop forming during meiosis
8
Q
Why does duplication alter the phenotype?
A
- related to gene dosage, shifts to one side
9
Q
Gene dosage
A
- balance of gene products must be maintained for some pathways
- interaction of certain gene products can lead to abnormal developments (position effect)
10
Q
Deletion of centromere can lead to
A
- loss of the entire chromosome because no segregation in meiosis/mitosis
11
Q
What happens if you lose essential genes?
A
- lethal if homozygous for loss
12
Q
What occurs in heterozygous deletions?
A
- gene products will be imbalanced
- allows recessive alleles on undeleted chromosome to be expressed (pseudo-dominance)
- some genes have to be present in two copies to produce enough gene product (haploin-insufficient)
13
Q
Example of a haploin-insufficient case
A
- Notch Locus
- heterozygous notch deletion
14
Q
Deletions lead to problems during what?
A
- chromosome pairing
15
Q
Inversions are another example of _______
A
- troubling chromosomal rearrangements
16
Q
Paracentric Inversions
A
- inversions that do not include the centromere in the inverted region
17
Q
Pericentric inversions
A
- inversions that include the centromere in the inverted region
18
Q
Inversion
A
- gene order is changed, can break a gene into 2
19
Q
What is the position effect?
A
- regulation of genes is sometimes context dependent
- order related/which genes are interacting
20
Q
The inversion loop is ______, present in _____
A
- characteristic
- meiosis
21
Q
In pericentric inversion a dicentric bridge can occur what is this?
A
- bridge between two chromosomes attached to a centromere
22
Q
Translocation
A
- movement between nonhomologous chromosomes
- not crossing over
- between homologous recombination
23
Q
Nonreciprocal translocation
A
- movement one way
- from one chromosome to another without equal exchange
24
Q
Reciprocal translocation
A
- movement 2 ways
- from one chromosome to another with equal exchange
25
What can result from translocation?
1. altered gene expression due to position effect (ex: Burkitt lymphoma)
2. Break may occur in a gene
- lose gene completely
26
Robertsonian translocation
- translocation and deletion
- forms a metacentric chromosome
- causes some forms of down syndrome
27
What can result from robertsonian translocation?
1. some forms of down syndrome
| 2. possible origin of a reciprocal translocation between two nonhomologous chromosomes
28
What can happen if segragation in translocation occurs during meiosis
- 1/3 possible outcomes
1. alternate segregation
2. adjacent 1 segregation
3. adjacent 2 segregation
29
What happens in alternate and adjacent 1 segregation?
- homologous centromeres segregate to opposite poles
30
After anaphase 2 in alternate segregation what happens to the gametes?
- they are viable
31
After anaphase 2 in adjacent 1 and 2 segregation what happens to the gametes?
- they are nonviable
32
Aneuploidy
- changes the number of individual chromosomes
33
How can aneuploidy occur?
1. loss of chromosome which has lost its centromere
2. robertsonian translocation
3. nondisjunction
34
Types of aneuploidy
1. Nullisomy
2. Monosomy
3. Trisomy
4. Tetrasomy
35
Nullisomy
- loss of both members of homologous pairs
| - 2n-2
36
n is equal to..
- the haploid number of chromosomes
| - humans 2n=46
37
Monosomy
- loss of a single chromosome
| ex: Turners syndrome
38
Trisomy
- gain of a single chromosome, resulting in three homologous chromosomes
ex: down syndrome (21)
39
Tetrasomy
- gain of two homologous chromosomes, resulting in four homologous chromosomes
- 2n+2
40
What is an organism with an extra copy of two different chromosomes
- double trisomic
41
Jimson Weed
- all different chromosomes, all different trisomics
42
What is the best tolerated aneuploidy?
- XYY has very little impact, due to the lack of genetic info on the Y
43
Examples of human aneuploidys
1. Turners Syndrome (XO)- lethal in males, females is viable
| 2. Klinefelter Syndrome (XXY)
44
Are autosomal or sex chromosome aneuploidys more tolerated?
- autosomal because smaller chromosomes
| - down syndrome (21) has about 300 genes
45
Most aneuploidys result from nondisjunction in father or mother?
- 75% is from nondisjunction in mother
46
Incidence of primary down syndrome increases with what?
- maternal age
47
Familial down syndrome
- translocation of a part of chromosome 21
| - runs in families, parents have undergone a robertsonian translocation
48
Down syndrome results from?
- a trisomy of chromosome 21
| - nondisjunction in meiosis 1 or 2 in female gamete
49
Trisomy 18
- type of autosomal aneuploids
| - Edward Syndrome, severe problems, most die by age of 1
50
Trisomy 13
- type of autosomal aneuploids
- Patau syndrome
- 50% die within 1 month
- 95% die by age 3
51
Trisomy 8
- mosaic individuals can have normal life expectancy
52
Trisomic Rescue
- Trisomy that is resolved by loss of a chromosome during embryogenesis
53
Uniparental Disomy
- occurs when both chromosomes are inherited from one parent
| - can result from trisomic rescue
54
Chromosome Mosaicism
- an organism can have normal tissues and tissues that have chromosome abnormalities that result from nondisjunction
55
Example of chromosome mosaicism
- Gynandromorph
- is both sexes XX and XO
- has a red eye and wild type wing
- also has a white eye and mini wing
56
How does polyploidy arise?
1. errors in meiosis
2. events at fertilization
3. errors in mitosis following fertizilization
57
Dispermy
- one at fertilization mechanism
- simultaneous fertilization of one egg with two sperm
- 75% have two sets of paternal chromosomes
58
What is the most common Polyploidy in humans?
- triploidy
| - found in 15-18% of spontaneous abortions
59
Autopolyploidy
- extra chromosome sets are derived from same species
60
Allopolyploidy
- extra chromosome sets are derived from different species
61
What are the problems with meiosis when polyploidy?
- usually results in sterility
62
How does alloploidy occur?
- as a result of hybridization followed by chromosomes doubling
63
What is an example of an alloploidy
- modern wheat
64
What are fragile sites
- a heritable gap of a chromosome that can be induced to generate chromosome breaks
65
Fragile X syndrome
- most common form of inherited mental impairment
| - results from increase in number of trinucleotide repeats
66
What does trinucleotide expansion and premutation lead to
- methylation and blockage of transcription
| - fragility is related to length of repeat region
67
Genetic anticipation
- the number of repeats increases in future generations causing symptoms to worsen
68
Polyploidy
- addition of entire chromosome sets
69
Types of duplications (can be good)
1. gene redundancy and amplification
2. gene families
3. pseudogenes- looks like a gene but is nonfunctional
70
Robertsonian translocation and evolution have the only major structural differences of
1. a number of pericentric and paracentric inversions
2. the recent fusion of two chromosomes to form human chromosome 2
3. a reciprocal translocation between the gorilla chromosomes which correspond to human chromosomes 5 and 17
71
Types of aneuploidy that are NOT a result of nondisjunction
1. inversion- seg bks and reverses orientation and reattaches
2. deletion- seg bks off and never returns
3. duplication- seg bks off and attatches to homologous chromosome, deletes from og
4. translocation- seg bks off and attatches to a nonhomologous chromosome
