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Principles of Disease-Megan > Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities > Flashcards

Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities Flashcards

1
Q

Describe the structure of a chromosome

A 
Linear chromosome
Telomere
Centromere
Heterochromatin
Euchromatin
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2
Q

Describe the features of telomeres

A

Have 5’-TTAGGG-3’ repeats

Hundreds of copies being present at the end of the chromosomes

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3
Q

How long are human telomeres

A

10-15 kb

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4
Q

How many base pairs do telomeres lose during mitosis

A

About 100

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5
Q

What are the 4 phases of the cell cycle

A

G1 -gap phase
S
G2 - gap 2
M - mitosis

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6
Q

What can occur after mitosis

A

Cells may cease division

Others may begin the cell cycle again

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7
Q

What happens in G1

A

Cell grows

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8
Q

What happens in G2

A

Cell prepares to divide

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9
Q

What happens in S

A

Cell replicates

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10
Q

What happens in M

A

Cell divison

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11
Q

How long does G1 last

A

10-12 hours

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12
Q

How long does S last

A

6-8 hours

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13
Q

How long does G2 last

A

2-4 hours

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14
Q

How long does M last

A

1-2 hours

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15
Q

How many phases of mitosis are there

A

5

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16
Q

Name the phases of mitosis

A 
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

PMAT C

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17
Q

What occurs in prophase

A

Chromosomes condense
Nuclear membrane disappears
Spindle fibres form from the centriole

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18
Q

What occurs in metaphase

A

Chromosomes are aligned at the equator of the cell
They are attached by fibres to each centriole
This is the maximum condensation of the chromosome

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19
Q

What occurs in anaphase

A

Sister chromatids separate longitudinally at the centromere and move to opposite ends of cell

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20
Q

What occurs in telophase

A

New nuclear membranes form

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21
Q

How many chromosomes are there in a diploid cell

A

Each diploid cell contains 46 chromosomes

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22
Q

What occurs in cytokineis

A

Cytoplasm separates

Two new daughter cells are formed

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23
Q

What are centromeres

A

Constricted regions which join the sister chromatids together (middle part of chromosome)

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24
Q

Describe centromeres

A

They have repetitive DNA sequences called satellite DNA

Are the site of kinetochore

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25
Q

What is a kinetochore

A

The kinetochore is the protein complex which binds to microtubules
It is required for chromosome separation during cell division

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26
Q

What is interphase

A

The phases:
G1
S
G2

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27
Q

What is heterochromatin

A

Condensed structure in silenced genes

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28
Q

What is euchromatin

A

Open structure in active genes

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29
Q

How many base pairs are there in DNA

A

About 3 billion

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30
Q

How many genes are in DNA

A

20-30,000 genes

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31
Q

How much of DNA is protein-coding

A

About 2%

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32
Q

What are satellite and minisatellite sequences

A

Tandemly repeated DNA sequences

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33
Q

Describe satellite DNA

A

14-500 bp repeats in 20-100 kb arrays at centromeres and telomeres

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34
Q

Describe minsatellite DNA

A

15-100 bp repeats in 1-5 kb arrays used for DNA fingerprinting

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35
Q

How much of the genome do highly repeated interspersed DNA sequences account for

A

About 45%

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36
Q

What does SINEs stand for

A

Short interspersed nuclear elements

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37
Q

What does LINEs stand for

A

Long interspersed nuclear elements

38
Q

How many base pairs do SINEs have

A

100-400 bp

Most common are Alu elements

39
Q

How many base pairs do LINEs have

A

Up to 6 kb

Most common are L1 elements

40
Q

What is chromatin

A

DNA packaged with histone proteins to form the chromatin

41
Q

What charge do histone proteins have

A

Positive

42
Q

What can histones be packaged into

A

Nucleosomes

43
Q

Describe the structure of nucleosomes

A

146 bp DNA wrapped 1.8 turns around a core of 8 histone proteins

44
Q

What kind of structure does chromatin resemble

A

Beads on a string

45
Q

How can a solenoid structure be formed

A

By the further wrapping to about 6 nucleosomes per turn

46
Q

Describe the solenoid structure

A

Compacted DNA by about a factor of 40

47
Q

How condensed is DNA at metaphase

A

By a factor of 10,000

48
Q

How many levels are there to the condensed chromatin structure

A

4

49
Q

What are the 4 levels of condensed chromatin structure

A

Level 1 - Nucleosome
Level 2 - Chromatin fibre
Level 3 - Fibre-scaffold complex
Level 4 - Chromosome

50
Q

Why is DNA packaging important

A

Negatively charged DNA can be neutralised by the positively charged histone proteins
Causes DNA to take up less space
Inactive DNA can be folded into inaccessible locations until required

51
Q

What are the three categories of chromosomes

A

Metacentric
Submetacentric
Acrocentric

52
Q

What is the main feature of metacentric chromosomes

A

The p length is roughly equal to the q length

53
Q

What is the main feature of submetacentric chromosomes

A

the p length is smaller than the q length

54
Q

What is the main feature of acrocentric chromosomes

A

the p length is much less than the q length

55
Q

Describe the procedure of chromosome analysis (Karotyping)

A

Analysed by using 5 ml of venous blood
Red cells are separated so only a white cell suspension remains
Culture medium is added
Incubation for 3 days at 37⁰C
Colchicine is added
White cells are separated off
Hypotonic saline added
Cells are fixed and spread onto the slide by dropping
These are stained and photographed and then the karyotypes can be identified

56
Q

Which chromosomes are metacentric

A

1 2 3 16 19 20 X

57
Q

Which chromosomes are submetacentric

A

4 8 6 7 8 9 10 11 12 17 18

58
Q

Which chromosomes are acrocentric

A

13 14 15 21 22 Y

59
Q

What does FISH stand for

A

Fluorescent in situ hybridisation

60
Q

How many probes does FISH have

A

4

61
Q

Name the 4 FISH probes

A

Unique sequence probes
Centromeric probes
Telomeric probes
Whole chromosome probes

62
Q

What are centromeric probes useful for

A

Determining chromosome numbers

63
Q

What are telomeric probes useful for

A

Detecting subtelomeric rearrangements that are often present in children with unexplained mental retardation

64
Q

What are whole chromosome probes

A

They are a cocktail of probes that cover different parts of a particular chromosome

65
Q

What can whole chromosome probes be used with

A

They can be used with different fluorescent dyes for spectral karyotyping

66
Q

What are whole chromosome probes useful for

A

Detecting translocations and rearrangements

67
Q

What is meiosis

A

The type of cell division which occurs in germ cells

68
Q

Where are diploid cells found for meiosis

A

Ovaries

Testes

69
Q

What happens to the diploid cells in meiosis

A

Divide to form haploid cells

70
Q

How may chromosomes do haploid cells have

A

23

71
Q

What happens to chromosomes in meiosis and what does this create

A

They are passed on as rearranged (recombined) copies

Creates genetic diversity

72
Q

What is the defining event in sexual reproduction and when does it occur

A

Recombination between homologs

Prophase

73
Q

How many phases are there in meiosis

A

Prophase I
Metaphase I
Anaphase I
Telophase I

74
Q

What occurs in prophase I

A

The recombination between non-sister chromatids

75
Q

How many times does the meiotic division occur in once cell cycle

A

2

76
Q

How many gametes are produced from a single meiotic cell cycle

A

4

77
Q

What is oogenesis

A

Process of egg formation

78
Q

Whats is spermatogenesis

A

Process of sperm formation

79
Q

What is increased in spermatogenesis compared to oogenesis

A

Spermatogenesis has more cell divisions so there is more of a chance of mutation

80
Q

When does gametogenesis commence in males and females

A

Males: Puberty
Females: Early embryonic life

81
Q

How long does gametogenesis take in

A

Males: 60-65 days
Females: 10-50 years

82
Q

What is the number of mitoses in gamete formation in gametogenesis

A

Males 30-500

Females: 20-30

83
Q

How many gametes are produced per mitosis in gametogenesis

A

Males: 4 spermatids
Females: 1 ovum and 3 polar bodies

84
Q

How many gametes are produced in gametogenesis

A

Males: 100-200 million
Females: 1 ovum per menstrual cycle

85
Q

Which two haploid cells can combine to form a diploid cell

A

Egg

Sperm

86
Q

What is the diploid cell formed from two haploid cells called

A

Zygote

87
Q

What is the sex of the embryo dependent on

A

Whether the sperm contains an X or Y chromosome

88
Q

What does an embryo contain

A

An assortment of genes from each original parent to produce more genetic diversity

89
Q

Where does the mitochondria (and its DNA) in the embryo come from

A

Mother via the egg

90
Q

What occurs in the early embryo of female mammals

A

Random inactivation of one X

91
Q

What is X inactivation

A

The inactivation of one X chromosome in female cells as only one X chromosome is sufficient for survival (like in males)

Think of tortoiseshell cats example

Principles of Disease-Megan (41 decks)

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