Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities Flashcards
1
Q
Describe the structure of a chromosome
A
Linear chromosome Telomere Centromere Heterochromatin Euchromatin
2
Q
Describe the features of telomeres
A
Have 5’-TTAGGG-3’ repeats
Hundreds of copies being present at the end of the chromosomes
3
Q
How long are human telomeres
A
10-15 kb
4
Q
How many base pairs do telomeres lose during mitosis
A
About 100
5
Q
What are the 4 phases of the cell cycle
A
G1 -gap phase
S
G2 - gap 2
M - mitosis
6
Q
What can occur after mitosis
A
Cells may cease division
Others may begin the cell cycle again
7
Q
What happens in G1
A
Cell grows
8
Q
What happens in G2
A
Cell prepares to divide
9
Q
What happens in S
A
Cell replicates
10
Q
What happens in M
A
Cell divison
11
Q
How long does G1 last
A
10-12 hours
12
Q
How long does S last
A
6-8 hours
13
Q
How long does G2 last
A
2-4 hours
14
Q
How long does M last
A
1-2 hours
15
Q
How many phases of mitosis are there
A
5
16
Q
Name the phases of mitosis
A
Prophase Metaphase Anaphase Telophase Cytokinesis
PMAT C
17
Q
What occurs in prophase
A
Chromosomes condense
Nuclear membrane disappears
Spindle fibres form from the centriole
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
19
Q
What occurs in anaphase
A
Sister chromatids separate longitudinally at the centromere and move to opposite ends of cell
20
Q
What occurs in telophase
A
New nuclear membranes form
21
Q
How many chromosomes are there in a diploid cell
A
Each diploid cell contains 46 chromosomes
22
Q
What occurs in cytokineis
A
Cytoplasm separates
Two new daughter cells are formed
23
Q
What are centromeres
A
Constricted regions which join the sister chromatids together (middle part of chromosome)
24
Q
Describe centromeres
A
They have repetitive DNA sequences called satellite DNA
Are the site of kinetochore
25
What is a kinetochore
The kinetochore is the protein complex which binds to microtubules
It is required for chromosome separation during cell division
26
What is interphase
The phases:
G1
S
G2
27
What is heterochromatin
Condensed structure in silenced genes
28
What is euchromatin
Open structure in active genes
29
How many base pairs are there in DNA
About 3 billion
30
How many genes are in DNA
20-30,000 genes
31
How much of DNA is protein-coding
About 2%
32
What are satellite and minisatellite sequences
Tandemly repeated DNA sequences
33
Describe satellite DNA
14-500 bp repeats in 20-100 kb arrays at centromeres and telomeres
34
Describe minsatellite DNA
15-100 bp repeats in 1-5 kb arrays used for DNA fingerprinting
35
How much of the genome do highly repeated interspersed DNA sequences account for
About 45%
36
What does SINEs stand for
Short interspersed nuclear elements
37
What does LINEs stand for
Long interspersed nuclear elements
38
How many base pairs do SINEs have
100-400 bp
| Most common are Alu elements
39
How many base pairs do LINEs have
Up to 6 kb
| Most common are L1 elements
40
What is chromatin
DNA packaged with histone proteins to form the chromatin
41
What charge do histone proteins have
Positive
42
What can histones be packaged into
Nucleosomes
43
Describe the structure of nucleosomes
146 bp DNA wrapped 1.8 turns around a core of 8 histone proteins
44
What kind of structure does chromatin resemble
Beads on a string
45
How can a solenoid structure be formed
By the further wrapping to about 6 nucleosomes per turn
46
Describe the solenoid structure
Compacted DNA by about a factor of 40
47
How condensed is DNA at metaphase
By a factor of 10,000
48
How many levels are there to the condensed chromatin structure
4
49
What are the 4 levels of condensed chromatin structure
Level 1 - Nucleosome
Level 2 - Chromatin fibre
Level 3 - Fibre-scaffold complex
Level 4 - Chromosome
50
Why is DNA packaging important
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
What are the three categories of chromosomes
Metacentric
Submetacentric
Acrocentric
52
What is the main feature of metacentric chromosomes
The p length is roughly equal to the q length
53
What is the main feature of submetacentric chromosomes
the p length is smaller than the q length
54
What is the main feature of acrocentric chromosomes
the p length is much less than the q length
55
Describe the procedure of chromosome analysis (Karotyping)
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
Which chromosomes are metacentric
1 2 3 16 19 20 X
57
Which chromosomes are submetacentric
4 8 6 7 8 9 10 11 12 17 18
58
Which chromosomes are acrocentric
13 14 15 21 22 Y
59
What does FISH stand for
Fluorescent in situ hybridisation
60
How many probes does FISH have
4
61
Name the 4 FISH probes
Unique sequence probes
Centromeric probes
Telomeric probes
Whole chromosome probes
62
What are centromeric probes useful for
Determining chromosome numbers
63
What are telomeric probes useful for
Detecting subtelomeric rearrangements that are often present in children with unexplained mental retardation
64
What are whole chromosome probes
They are a cocktail of probes that cover different parts of a particular chromosome
65
What can whole chromosome probes be used with
They can be used with different fluorescent dyes for spectral karyotyping
66
What are whole chromosome probes useful for
Detecting translocations and rearrangements
67
What is meiosis
The type of cell division which occurs in germ cells
68
Where are diploid cells found for meiosis
Ovaries
| Testes
69
What happens to the diploid cells in meiosis
Divide to form haploid cells
70
How may chromosomes do haploid cells have
23
71
What happens to chromosomes in meiosis and what does this create
They are passed on as rearranged (recombined) copies
| Creates genetic diversity
72
What is the defining event in sexual reproduction and when does it occur
Recombination between homologs
| Prophase
73
How many phases are there in meiosis
Prophase I
Metaphase I
Anaphase I
Telophase I
74
What occurs in prophase I
The recombination between non-sister chromatids
75
How many times does the meiotic division occur in once cell cycle
2
76
How many gametes are produced from a single meiotic cell cycle
4
77
What is oogenesis
Process of egg formation
78
Whats is spermatogenesis
Process of sperm formation
79
What is increased in spermatogenesis compared to oogenesis
Spermatogenesis has more cell divisions so there is more of a chance of mutation
80
When does gametogenesis commence in males and females
Males: Puberty
Females: Early embryonic life
81
How long does gametogenesis take in
Males: 60-65 days
Females: 10-50 years
82
What is the number of mitoses in gamete formation in gametogenesis
Males 30-500
| Females: 20-30
83
How many gametes are produced per mitosis in gametogenesis
Males: 4 spermatids
Females: 1 ovum and 3 polar bodies
84
How many gametes are produced in gametogenesis
Males: 100-200 million
Females: 1 ovum per menstrual cycle
85
Which two haploid cells can combine to form a diploid cell
Egg
| Sperm
86
What is the diploid cell formed from two haploid cells called
Zygote
87
What is the sex of the embryo dependent on
Whether the sperm contains an X or Y chromosome
88
What does an embryo contain
An assortment of genes from each original parent to produce more genetic diversity
89
Where does the mitochondria (and its DNA) in the embryo come from
Mother via the egg
90
What occurs in the early embryo of female mammals
Random inactivation of one X
91
What is X inactivation
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
