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Molecular Genetics > Lecture 1 - Higher Eukaryotic Chromosomes > Flashcards

Lecture 1 - Higher Eukaryotic Chromosomes Flashcards

1
Q

What is a Telomere?

A

Area of repetitive DNA and end of chromosomes

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2
Q

Are telomere stable?

A

Yes and they do not fuse with other chromosomes

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3
Q

What is a centomere?

A

Region or kinetocore where the cells spindle fibres attach

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4
Q

What are sister chromatids?

A

Identical copies formed in DNA replication - both copies are joined together by the centromere

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5
Q

How is DNA packaged into a nucleus?

A

DNA is wrapped to make ball like structures they then form chromatin fiber to form metaphase chromosome

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6
Q

What grooves open up when the DNA wraps around the nucleosome?

A

Minor groove

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7
Q

What makes the DNA relaxed?

A

The longer the linker DNA

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8
Q

What is found near the centromere?

A

Heterochromatin

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9
Q

What happens to telomeres with age?

A

Shorten

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10
Q

What is it called when the centromere is in the centre of the chromosome?

A

Metacentric chromosome

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11
Q

Where is the centromere in a submetacentric chromosome?

A

Top of the chromosome, makes a smaller short arm than long arm

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12
Q

What is it called when the centromere is at the very top of the chromosomes?

A

Acrocentric

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13
Q

What are satellites?

A

Secondary constriction site with small chromosomal segment

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14
Q

What does a secondary constriction site on a chromosome act as?

A

Acts as a nuclear organisation region (NOR)

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15
Q

What chromosomes do we find Satellites on?

A

13, 14, 15, 21 and 22

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16
Q

What is the stain used to distinguish between similar chromosomes?

A

Giemsa staining (g-banding)

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17
Q

When using giemsa staining what regions stain darker and why?

A

Heterochromatic regions (AT-rich) and are gene poor

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18
Q

When using giemsa staining why are some bands stained light?

A

GC rich and more active

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19
Q

What stops the protein from holding DNA together before giemsa can stain?

A

Trypsin

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20
Q

What is the international system of human cytogenetic nomenclature (ISCN)?

A

Database showing all the chromosome bands allowing us to locate specific regions and find abnormalities

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21
Q

Why do we have the international system of human cytogenetic nomenclature (ISCN)?

A

Good for accurate and consistent description of genomic changes as identified by karyotyping

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22
Q

What is the short arm labelled as?

A

XP

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23
Q

What is the king arm labelled as?

A

XQ

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24
Q

How do you accurately locate positions for specific genes?

A

FISH

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25
Q

How do you do fish?

A

Isolate metaphase chromosomes and spread in glass slide.
Meanwhile clone a gene of interest and make a DNA probe by adding it to a plasmid - fluorescent it label this.
Then add dye to the DNA (direct labelling) or add biotin then later the dye by adding streptavidin with dye on it which will react with biotin (indirect labelling).

Denature chromosomes and probe and the gene of interest will hybridise to the chromosome. You can now see the gene of interests location

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26
Q

Can you do FISH for more than one gene?

A

Yes - multicolour FIsH

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27
Q

How does digital karyotyping work?

A

Uses short sequence tags taken from specific genomic loci ti provide a quantitative and high-resolution view of copy number changes in a genome wide scale

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28
Q

How can Digital karyotyping help you see abnormalities and how does it work?

A

Genome fragmented into small pieces and labelled

Once labelled it’s hybridised too an array of DNA probes which span the wholes gene

A computer will then see the amount of fluorescence and you can see if there is any abnormalities

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29
Q

What is polyploidy?

A

One or more additional chromosomes sets e.g triploidy is 3 copies of the haploid chromosome

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30
Q

What is aneuploidy?

A

Loss or gain of genetic material from a single chromosome

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31
Q

In aneuploidy what is a monosomy?

A

Loss of one chromosome

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32
Q

In aneuploidy what is a trisomy?

A

Gain of one chromosome

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33
Q

What is the most common cause of aneuploidy?

A

Nondisjunction in meiosis

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34
Q

What are some structural abnormalities?

A

Deletions, duplications, inversions and translocations

35
Q

What is nondisjunction?

A

Failure of the chromosomes to unjoin resulting in them going into the same daughter cells

36
Q

What happens if nondisjunction happens in the first division?

A

One daughter cell gets both sets of chromosomes

37
Q

What happens if nondisjunction happens in the 2nd meitotic division?

A

The Nondisjunction would leas ti one daughter cell having 2 chromosomes and one having non. However the 3rd and 4th could be normal depending on if only one daughter cell suffered the nondisjunction

38
Q

What is Turner syndrome?

A

One copy of X chromosomes due to aneuploidy

39
Q

What is Klinefelter syndrome?

A

Males have one extra X chromosome (XXY)

40
Q

What happens in trisomy X

A

Females have an extra X chromosomes (XXX)
And makes get an extra y (XYY).

41
Q

What is seen in spontaneous abortions?

A

Every possible trisomy

42
Q

Example of trisomy?

A

Down syndrome

43
Q

Examples of lethal trisomy’s?

A

Patau syndrome and Edward syndrome

44
Q

What are the 4 ways chromosomes can be rearranged ti cause structural abnormalities?

A

Duplication, deletion, inversion and translocation

45
Q

What happens in a duplication?

A

Prices of genome duplicated

46
Q

What happens in a deletion?

A

Chromosome fragment lost

47
Q

What happens in inversion?

A

DNA fragment reversed

48
Q

What happens in translocation?

A

Chromosome fragment moved to different strand

49
Q

What is reciprocal translocation?

A

Two DBA fragments have changed their position

50
Q

What are Consequences if rearranged chromosomes?

A

Change in gene dosage in deletion and duplication leading to unbalanced genes

51
Q

Why are inversions easier ti tolerate than duplication and deletions?

A

The gene dosage remains the same so no unbalanced chromosomes

52
Q

What is a Paracentric inversion?

A

Centromeres are parallel which conserves location if centromeres

53
Q

What does pericentric mean with inversion?

A

The centromeres aren’t parallel which changes the order of genes and the location of centromeres

This affects meiosis and next generation

54
Q

Where are low copy repeats found and what does non-allergic homologous recombination (NAHR) between two LCR’s lead ti?

A

These are interspersed throughout the genome and a NAHR between 2 LCRs can lead ti deletion or tandem duplications of the flanking area of the genome

55
Q

Can you get crossover between homologous but non-alleic LCR?

A

Yes

56
Q

What are low copy repeats?

A

DNA sequences which appear the same in lots of different places in the genome

57
Q

In a duplication how many copies of a gene will you get?

A

3

58
Q

In a deletion how many copies of a gene is there?

A

1 copy deleted in one allele and one normal in the other allele

59
Q

Where are LCR’s found?

A

In hotspots

60
Q

What are balanced reciprocal translocations?

A

When a gene translocated with another gene and this doesn’t create a duplication or a deletion.

61
Q

What happens to carriers of balanced reciprocal translocations?

A

They are healthy and fertile but can transmit the unbalanced form to offspring.

62
Q

What would happen if the 4 chromosome reciprocal translocation structure was split adjacent 2 (vertically)?

A

It would be unbalanced

63
Q

What would happen to the 4 chromosomal structure reciprocal translocation is it was split horizontally (adjacent)?

A

Unbalanced

64
Q

What would happen if the 4 chromosomal reciprocal translocation structure was split alternatively?

A

It would be balanced

65
Q

What determines whether or not reciprocal translocations would lead to unbalanced or balanced segregation?

A

Depends of how they are segregated

66
Q

What are robertsonian translocations?

A

Centric fusion of two Acrocentric chromosomes

67
Q

How do robertsonian translocations work?

A

The long arm fuses with another arm of a different chromosomes when the DNA breaks.

68
Q

What arm has more genes?

A

Long arm.

69
Q

In robertsonian translocation what product is lost and why?

A

Short arm as there is no essential genea

70
Q

Is the robertsonian translocation balanced?

A

Yes

71
Q

What disease is caused by robertsonian translocation?

A

Down syndrome

72
Q

What is an example of a reciprocal translocation and how is it done and what does it cause?

A

Philadelphian chromosome where long arm of chromosome 9 fuses with chromosome 22. This can cause leukaemia.

73
Q

How do you diagnose the Philadelphia chromosome?

A

FISH

74
Q

What are copy number variations?

A

Small variations only seen through genome sequencing and causes human variation

75
Q

Are CNV’s lethal or neutral?

A

Both

76
Q

Do duplications of CNV’s go in tandem?

A

Yes

77
Q

What are the two CNV groups?

A

Long and short repeats

78
Q

Example of segmental duplication and evolution: AMY-1

A

People adapted to get more energy from starch food

79
Q

What do fixed segmental duplications generate?

A

Redundant genes free to evolve and can generate de novo rearrangements

80
Q

What do karyotypes need to evolve?

A

They need to be fixed and passed through the germ line through meiosis

81
Q

Do chromosomes from different species have the same ancesterol chromosome?

A

Yea

82
Q

If something is described as being syntenic what does this mean?

A

A situation in which genes are arranged in similar blocks in different species and the conserved order of genes between species

83
Q

When looking at blocks how can you tell how close the evolution is?

A

The smaller the number of blocks

84
Q

When looking at syntenic blocks between 2 species what does more conserved syntenic blocks mean?

A

There is more evolutionary rearrangement and they are close in evolution

Molecular Genetics (20 decks)

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