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GENETICS > Chromosomal Genetics II > Flashcards

Chromosomal Genetics II Flashcards

1
Q

Why are most cancers described as Clonal?

A

All the cancer cells contain the same genetic changes co can be traced back to the single mutated cell.

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2
Q

How can a Deletion cause cancer?

A

Deletion of Tumour Suppressor genes

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3
Q

How can Duplication cause cancer?

A

Duplication of Proto- Oncogenes

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4
Q

What are Proto-Oncogenes?

A

A family signalling molecules responsible for cell division activation and acceleration.

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5
Q

How can Translocations cause cancer?

A

Position Effect Variegation- cancer is initiated because gene controlling cell division is translocated and inactivated is caused.

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6
Q

Give an example of how Translocation can cause cancer

A

Burkitt’s Lymphoma- proto-oncogene C-MYC on C8 is moved to C14 next to gene controlling expression of antibodies in B-cells. C-MYC is more heavily expressed as it’s now in a highly transcribed region. Leads to uncontrolled mitosis of B-cells.

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7
Q

What is meant by Aneuploidy?

A

Individuals with chromosome numbers different from that of the normal number of their species.

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8
Q

What is the main cause of Aneuploidy?

A

Non-disjunction: a failure in the separation of homologous chromosomes at cell division.

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9
Q

Give an example of an Aneuploidy.

A

Down’s Syndrome- Trisomy 21 (3 C21). 88% cases caused by nondisjunction of maternal C21.

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10
Q

What is Klinefelter Syndrome an example of?

A

Aneuploidy- wrong numbers of sex chromosomes (usually extra). Usually compensated by Lyonization.

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11
Q

What is Turner’s Syndrome an example of?

A

Aneuploidy- only one X chromosome. Person is still female but sterile .

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12
Q

Define Polyploidization

A

Changes in the number of chromosome sets. Lethal in humans important in agriculture.

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13
Q

What is the difference between an Autopolyploid and an Allopolyploid

A

Auto- multiplication of number of sets WITHIN a species

Allo- hybridisation of species and mixing of chromosome sets.

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14
Q

What is the importance of Colchicine in Agriculture?

A

Increases the frequency of polyploidization. Odd number ploids can be made to be sterile (seedless grapes)

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15
Q

What is meant by the term Linkage

A

The principle that particular loci tend to accompany each other down the generations- the extent to which they do so varies on genes involved.

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16
Q

Outline the Experiments of Bateson and Punnet

A
  • Dihybrid Crosses purple dominant peas and long dominant grains
  • PP LL x pp ll
  • F1 = Pp Ll purple long
  • F2 = Recombinant deficiency (pp LL, PP ll) Excess in parental types (PP LL, pp ll)
17
Q

Outline the main problems using the Mendel design of cross in linkage analysis.

A
  • Phenotypically identical classes can be disguised as genetically the same
  • Statistically Inefficient to study recombinants
18
Q

Explain the principles of Morgan’s Back Cross.

A

WT female crossed with mutant male to make F1. Het females of F1 crossed with mutant male to make F2.

19
Q

What is the expected ratios of the Dihybrid Back Cross for the four genotypes?

A

1 : 1 : 1 : 1

20
Q

What was Morgan’s Hypothesis?

A

The deviation from Mendel’s 2nd is due to physical association (proximity) of loci in either parent - loci on the same pair of homologous chromosomes are linked.

21
Q

Why is linkage incomplete?

A

Due to crossing over during meiosis, loci on same chromosome may be separated and recombination may still occur.

22
Q

Name 5 stages involved in Chiasma Formation during Prophase I

A

Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.

23
Q

Outline the events that occur in Leptotene, Zygotene and Pachytene.

A

Leptotene - chromosomes become visible.
Zygotene - Homologous chromosome pair up and zip up, synapsis
Pachytene - the pairs get short and fat forming tetrads

24
Q

What occurs during Diplotene?

A

The tetrads open out and exchange material forming chiasmata. Occurs between any non-sister chromatids.

25
Q

What occurs during Diakinesis?

A

The contraction of chromosomes and movement toward the metaphase plate.

26
Q

Why can the frequency of recombination never rise above 50%?

A

For unlinked loci, the ration 1: 1: 1: 1 will hold in the Back Cross, hence 2 out of 4 classes will be recombinants.

27
Q

What does a recombination frequency of less than 50% suggest?

A

Linkage- the two genes are likely to be on the same chromosome.

28
Q

What was the suggestion of Sturtevant?

A

Variation of recombinant frequency was dependent on the distance apart of the loci in a frequency

29
Q

What is the equation for Recombination Frequency?

A

Recombinants/ Total

30
Q

What will increase the chance of loci being split by chiasma formation?

A

A larger distance between loci.

31
Q

Name 3 analytical techniques used in chromosome mapping.

A

GIEMSA, FISH and Somatic Cell Hybridisation.

32
Q

How can Giemsa staining be used to map chromosomes?

A

Giemsa preferentially stains A-T heterochromatic regions (tend to be non coding). The coding G-C rich regions are less condensed and less stained

33
Q

What does FISH stand for?

A

Fluorescent In Situ Hybridisation

34
Q

What is FISH used to localize?

A

Used to localize the presence or absence of specific DNA sequences on chromosomes

35
Q

How does FISH work?

A
  • Complementary sequence to target is constructed (probe)

- Probe is attached to biotin-avidin and a fluorophore. If sequence is present, probe will bind and light up.

36
Q

Outline the principles of Somatic Cell Hybridisation.

A
  • Human cells are fused with mouse cells.
  • Human chromosomes are spat out of hybrid cells
  • Missing characteristics are associated with genes on missing chromosomes
37
Q

How are Mouse and Human cells made to fuse?

A

Sendai Virus- an RNA virus can bind to both human and mice cells simultaneously. As it inserts RNA into both cells they are brought together and forced to fuse.

38
Q

How is the Sendai virus able to bind to both human and mice cells simultaneously?

A

The Sendai virus has several points of attachment.

GENETICS (7 decks)

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