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mol gen > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

Functional chromosomes have three parts

A

Centromere - attachment point for spindle fibers via kinetochores
A pair of Telomeres - Protect ends of the chromosome
Origins of Replication - Sites where DNA synthesis begins

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2
Q

Cytogenetics

A

The study of chromosome number and structure

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3
Q

Most cytological studies are done on what type of cells

A

dividing cells

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4
Q

What type of cells are used for human studies?

A

White blood cells

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5
Q

Why is WBC good to use in human studies?

A

They are arrested in mitosis by using chemicals that inhibit formation of the mitotic spindle (colchicine)
When they are put in a hypotonic solution the cells swell
They then can be spread on a microscope slide

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6
Q

What can chromosomes do so that they can be distinguished by?

A

They can be stained and each chromosome has a characteristic banding pattern with a particular stain

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7
Q

Chromosomes with Q banding are stained with?

A

Quinacrine - It produces a striped or banded appearance

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8
Q

Q banding

A

Bands appear under UV light
Highly reproducible
Individual chromosomes can be identified so structural abnormalities can be seen

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9
Q

What is Geimsa?

A

A non-fluorescent dye, that also produces bands

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10
Q

G-banding

A

produces bands that correspond to the bands of Q-banding

Stains areas rich in A-T pairs

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11
Q

Which banding stains the region around each centromere?

A

C-banding

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12
Q

R-banding

A

Produces bands corresponding to the light bands in Q-banding

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13
Q

Process of R-banding

A

Cells are heated in a phosphate buffer prior to Geisma staining
The cells are then stained with acridine orange
It produces the reverse of G-banding

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14
Q

Types of Chromosome mutations

A

Alterations in the structure of chromosomes
Aneuploidy
Polyploidy

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15
Q

What is aneuploidy?

A

The number of chromosomes are altered.
One or more individual chromosomes is deleted or added.
There is a genetic imbalance.

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16
Q

What is polyploidy?

A

One or more entire sets of chromosomes is added.

No genetic imbalance

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17
Q

What is euploidy?

A

The normal number of sets of chromosomes.

In humans that is diploid.

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18
Q

Polyploidy seems to confer…..

A

larger size but normal proportions.

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19
Q

Aneuploidy can do what to an organism..

A

It can alter its shape and proportions in characteristic ways

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20
Q

Gene dosage effect

A

The relationship between the number of copies of a gene and the amount of gene product made.

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21
Q

Chromosome Rearrangements

A

Duplication, Deletion, Inversion, Transocation

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22
Q

Tandem Duplication

A

The duplicated segment is immediately adjacent to the original segment

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23
Q

Displaced Duplication

A

The duplicated segment is located at a distance from the original on the same chromosome or on another

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24
Q

Reverse Duplication

A

The duplication is inverted

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25
Q

When can duplication cause problems?

A

With pairing in meiosis in the heterozygote

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26
Q

With a duplicate gene,they are how many times the normal gene product?

A

1.5

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27
Q

Duplication causes what type of mutations in drosophila?

A

Bar eye mutations

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28
Q

Why is gene duplications common in evolution?

A

It provides a significant source of variation for evolution.

Mammalian hemoglobin genes arose by tandem duplication

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29
Q

If a deletion occurs in a heterozygote what must happen?

A

In meiosis, one side of the chromosome must loop out

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30
Q

What happens if the centromere is deleted?

A

The chromosome will not segregate in mitosis or meiosis and will be lost.

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31
Q

What happens in homozygous deletions?

A

Lethal

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32
Q

what happens in heterozygous deletions?

A

may produce gene dosage imbalance.
Pseudo dominance - recessive phenotypes may be uncovered if the dominant allele is lost.
Haploinsufficient - A single copy of the gene does not produce enough product to produce the wild-type phenotype.

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33
Q

A syndrome caused by deletion

A

Cri-du-chat: Loss of segment on the short arm of one copy of chromosome 5 ( 46 (5p) )

34
Q

Wolf - Hirschhorn syndrome (midline closure defect)

A

Deletion.

Loss of segment on the short arm of one copy of chromosome 4 (46 (4p) ).

35
Q

Williams - Beuren syndrome

A

Loss of a small segment of chromosome 7- long arm (26 genes).
Elfin features

36
Q

Inversion

A

A chromosomal segment is turned 180

37
Q

Paracentric

A

Inversion that do not include the centromere. Does not change the size of the arms

38
Q

Pericentric

A

Inversions that do include the centromere. May change the size of the arms.

39
Q

What difficulties is produced for heterozygotes for inversion during meiosis.

A

This pairing causes stress in the chromosome.
The pairs may come apart inappropriately.
Depends on where the cut occurs.

40
Q

If inversion occurs outside the areas of a gene…

A

Usually do not lead to phenotypic abnormalities.

Can be bred to homozygosity.

41
Q

Inversion occurs within the area of a gene…

A

May produce a phenotypically detectable change, and may produce a new gene function.
May be a lethal gene, and cannot be bred to homozygosity

42
Q

Why does inversion take place?

A

Irradiation, or naturally by the action of transposable elements, or may be a result of mechanical sheer

43
Q

What is Position Effect?

A

When inversion takes place and changes the order of genes and may cause them to be expressed at inappropriate times or in the wrong tissue

44
Q

Crossovers within inversions produce abnormal chromatids (from prophase 1 of meiosis)

A

2 normal chromatids, one with 2 centromere, and one with no centromere (4 total).

45
Q

In Anaphase 1 what happens….

A

the centromeres separate stretching the dicentric chromatid, which breaks it. The chromosome with no centromere is lost.

46
Q

Results after dicentric chromatid breaks

A

Two wild-type non recombinant chromosomes and two recombinant chromosomes that are missing some genes and will not produce viable offspring.

47
Q

Dicentric and acentric chromosomes

A

Neither will segregate properly in meiosis

48
Q

Dicentric bridge

A

Forms during anaphase of a dicentric chromosome

49
Q

Can recombinant progeny be produced in a heterozygote with an pericentric inversion

A

Few do. No acentric chromosomes or dicentric bridges are produced. The recombinant chromosomes are missing genes or have extra genes and produce inviable offspring.

50
Q

No recombinant progeny are produced in heterozygote with what?

A

Paracentric. Fertility is reduced for an inversion heterozygote.

51
Q

Which chromosome in humans and chimpanzees differ by a pericentric inversion

A

Chromosome 4

52
Q

ON EXAM* Translocation

A

Movement of genetic material between non-homologous chromosomes and from one are of a chromosome to another.

53
Q

Reciprocal Translocation

A

An exchange of chromosomes between two non-homologous chromosomes with no loss of genetic material.

54
Q

Effects of Translocation on the phenotype

A

Position effect.
Chromosomal breaks may occur within a gene disrupting its function.
Deletions frequently accompany translocation.

55
Q

Translocation cause difficulties in what…

A

Disjunction in meiosis

56
Q

Translocation heterozygotes formed from…

A

Aneuploid gametes will probably not be viable

57
Q

Euploid gametes

A

Have the same number of chromosomes: Monoploid, diploid, triploid, or tetraploid.

58
Q

Alternate disjunction

A

Only one that produces euploid gametes

59
Q

What produces aneuploid gametes

A

Adjacent disjunction I and II

60
Q

With euploid gametes from alternate disjunction how many gametes are viable.

A

Half

61
Q

Robertsonian Translocation

A

Two non-homologous chromosomes fuse at their centromeres and the short arms are lost.

62
Q

Fragile sites

A

Found mostly in males

63
Q

Nullisomy

A

Loss of both members of a homologous pair (2n-2)

64
Q

Monosomy

A

The loss of a single chromosome (2n-1)

65
Q

Trisomy

A

Gain of a single chromosome (2n +1)

66
Q

Tetrasomy

A

Gain of a single homologous pair of chromosomes (2n+2)

67
Q

Trisomy 16

A

Most common human aneuploid

68
Q

Partial Trisomy 16 individuals are…

A

Genetic mosaics in which only some of their cells have the extra chromosome

69
Q

Trisomy 21

A

Down Syndrome

70
Q

Primary Down Syndrome

A

Usually results from non-disjunction in Meiosis I in the female.
Not likely to reoccur in the family.
Incidence increases with maternal age.
Three complete copies of chromosomes.

71
Q

Familial Down Syndrome

A

Have 46 chromosomes but a small extra part of chromosome 21 is attached to another chromosome through translocation.
Runs in the family.
Can’t tell apart from primary downs

72
Q

Familial Downs frequently caused by which translocation?

A

Robertsonian Translocation between Chromosmes 21 and 14

73
Q

Which arms are lost in Robertsonian?

A

The short arms

74
Q

Description of carriers of Robertsonain?

A

Have 45 chromosomes but a normal phenotype.

75
Q

Patau Syndrome

A

Trisomy 13 (cleft palate)

76
Q

Edwards Syndrome

A

Trisomy 18

77
Q

Warkany Syndrome 2

A

Trisomy 8 (bulbous tipped nose)

78
Q

Uniparental Disomy

A

Both members of a homlogous pair of chromosmes are inherited from one parent

79
Q

Mosaicism

A

Results from nondisjunction in a mitotic division . All of it’s progeny have the abnormality.

80
Q

Gene dosage is not affected by….

A

Polyploidy

81
Q

What is the key event in the formation of polyploids?

A

Chromosome doubling.
Mitosis without cytokinesis.
Alteration of meiosis to produce unreduced gametes.

mol gen (3 decks)

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