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Fundamental genetics > Chapter 6 > Flashcards

Chapter 6 Flashcards

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Biology 101 flashcards
1
Q

karyotype

A
  • display of a complete set of chromosomes
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2
Q

Chromosomal mutation Types

A
  1. chromosomal rearrangements
  2. aneuploids
  3. euploids (polyploidy)
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3
Q

Aneuploids

A
  • the number of chromosomes is altered (addition/deletion)
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4
Q

euploids/polyploids

A
  • one or more complete sets of chromosomes are added
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5
Q

Tandem duplication

A
  • duplicated region is immediately adjacent(next to)
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6
Q

displaced duplication

A
  • located a distance away (even on another chromosome)
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7
Q

What is a characteristic of duplication?

A
  • loop forming during meiosis
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8
Q

Why does duplication alter the phenotype?

A
  • related to gene dosage, shifts to one side
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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)
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10
Q

Deletion of centromere can lead to

A
  • loss of the entire chromosome because no segregation in meiosis/mitosis
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11
Q

What happens if you lose essential genes?

A
  • lethal if homozygous for loss
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12
Q

What occurs in heterozygous deletions?

A
  1. gene products will be imbalanced
  2. allows recessive alleles on undeleted chromosome to be expressed (pseudo-dominance)
  3. some genes have to be present in two copies to produce enough gene product (haploin-insufficient)
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13
Q

Example of a haploin-insufficient case

A
  • Notch Locus

- heterozygous notch deletion

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14
Q

Deletions lead to problems during what?

A
  • chromosome pairing
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15
Q

Inversions are another example of _______

A
  • troubling chromosomal rearrangements
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16
Q

Paracentric Inversions

A
  • inversions that do not include the centromere in the inverted region
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17
Q

Pericentric inversions

A
  • inversions that include the centromere in the inverted region
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18
Q

Inversion

A
  • gene order is changed, can break a gene into 2
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19
Q

What is the position effect?

A
  • regulation of genes is sometimes context dependent

- order related/which genes are interacting

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20
Q

The inversion loop is ______, present in _____

A
  • characteristic

- meiosis

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21
Q

In pericentric inversion a dicentric bridge can occur what is this?

A
  • bridge between two chromosomes attached to a centromere
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22
Q

Translocation

A
  • movement between nonhomologous chromosomes
  • not crossing over
  • between homologous recombination
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23
Q

Nonreciprocal translocation

A
  • movement one way

- from one chromosome to another without equal exchange

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24
Q

Reciprocal translocation

A
  • movement 2 ways

- from one chromosome to another with equal exchange

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25
Q

What can result from translocation?

A
  1. altered gene expression due to position effect (ex: Burkitt lymphoma)
  2. Break may occur in a gene
    - lose gene completely
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26
Q

Robertsonian translocation

A
  • translocation and deletion
  • forms a metacentric chromosome
  • causes some forms of down syndrome
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27
Q

What can result from robertsonian translocation?

A
  1. some forms of down syndrome

2. possible origin of a reciprocal translocation between two nonhomologous chromosomes

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28
Q

What can happen if segragation in translocation occurs during meiosis

A
  • 1/3 possible outcomes
    1. alternate segregation
    2. adjacent 1 segregation
    3. adjacent 2 segregation
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29
Q

What happens in alternate and adjacent 1 segregation?

A
  • homologous centromeres segregate to opposite poles
30
Q

After anaphase 2 in alternate segregation what happens to the gametes?

A
  • they are viable
31
Q

After anaphase 2 in adjacent 1 and 2 segregation what happens to the gametes?

A
  • they are nonviable
32
Q

Aneuploidy

A
  • changes the number of individual chromosomes
33
Q

How can aneuploidy occur?

A
  1. loss of chromosome which has lost its centromere
  2. robertsonian translocation
  3. nondisjunction
34
Q

Types of aneuploidy

A
  1. Nullisomy
  2. Monosomy
  3. Trisomy
  4. Tetrasomy
35
Q

Nullisomy

A
  • loss of both members of homologous pairs

- 2n-2

36
Q

n is equal to..

A
  • the haploid number of chromosomes

- humans 2n=46

37
Q

Monosomy

A
  • loss of a single chromosome

ex: Turners syndrome

38
Q

Trisomy

A
  • gain of a single chromosome, resulting in three homologous chromosomes
    ex: down syndrome (21)
39
Q

Tetrasomy

A
  • gain of two homologous chromosomes, resulting in four homologous chromosomes
  • 2n+2
40
Q

What is an organism with an extra copy of two different chromosomes

A
  • double trisomic
41
Q

Jimson Weed

A
  • all different chromosomes, all different trisomics
42
Q

What is the best tolerated aneuploidy?

A
  • XYY has very little impact, due to the lack of genetic info on the Y
43
Q

Examples of human aneuploidys

A
  1. Turners Syndrome (XO)- lethal in males, females is viable

2. Klinefelter Syndrome (XXY)

44
Q

Are autosomal or sex chromosome aneuploidys more tolerated?

A
  • autosomal because smaller chromosomes

- down syndrome (21) has about 300 genes

45
Q

Most aneuploidys result from nondisjunction in father or mother?

A
  • 75% is from nondisjunction in mother
46
Q

Incidence of primary down syndrome increases with what?

A
  • maternal age
47
Q

Familial down syndrome

A
  • translocation of a part of chromosome 21

- runs in families, parents have undergone a robertsonian translocation

48
Q

Down syndrome results from?

A
  • a trisomy of chromosome 21

- nondisjunction in meiosis 1 or 2 in female gamete

49
Q

Trisomy 18

A
  • type of autosomal aneuploids

- Edward Syndrome, severe problems, most die by age of 1

50
Q

Trisomy 13

A
  • type of autosomal aneuploids
  • Patau syndrome
  • 50% die within 1 month
  • 95% die by age 3
51
Q

Trisomy 8

A
  • mosaic individuals can have normal life expectancy
52
Q

Trisomic Rescue

A
  • Trisomy that is resolved by loss of a chromosome during embryogenesis
53
Q

Uniparental Disomy

A
  • occurs when both chromosomes are inherited from one parent

- can result from trisomic rescue

54
Q

Chromosome Mosaicism

A
  • an organism can have normal tissues and tissues that have chromosome abnormalities that result from nondisjunction
55
Q

Example of chromosome mosaicism

A
  • Gynandromorph
  • is both sexes XX and XO
  • has a red eye and wild type wing
  • also has a white eye and mini wing
56
Q

How does polyploidy arise?

A
  1. errors in meiosis
  2. events at fertilization
  3. errors in mitosis following fertizilization
57
Q

Dispermy

A
  • one at fertilization mechanism
  • simultaneous fertilization of one egg with two sperm
  • 75% have two sets of paternal chromosomes
58
Q

What is the most common Polyploidy in humans?

A
  • triploidy

- found in 15-18% of spontaneous abortions

59
Q

Autopolyploidy

A
  • extra chromosome sets are derived from same species
60
Q

Allopolyploidy

A
  • extra chromosome sets are derived from different species
61
Q

What are the problems with meiosis when polyploidy?

A
  • usually results in sterility
62
Q

How does alloploidy occur?

A
  • as a result of hybridization followed by chromosomes doubling
63
Q

What is an example of an alloploidy

A
  • modern wheat
64
Q

What are fragile sites

A
  • a heritable gap of a chromosome that can be induced to generate chromosome breaks
65
Q

Fragile X syndrome

A
  • most common form of inherited mental impairment

- results from increase in number of trinucleotide repeats

66
Q

What does trinucleotide expansion and premutation lead to

A
  • methylation and blockage of transcription

- fragility is related to length of repeat region

67
Q

Genetic anticipation

A
  • the number of repeats increases in future generations causing symptoms to worsen
68
Q

Polyploidy

A
  • addition of entire chromosome sets
69
Q

Types of duplications (can be good)

A
  1. gene redundancy and amplification
  2. gene families
  3. pseudogenes- looks like a gene but is nonfunctional
70
Q

Robertsonian translocation and evolution have the only major structural differences of

A
  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
Q

Types of aneuploidy that are NOT a result of nondisjunction

A
  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

Fundamental genetics (15 decks)

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