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Flashcards in Chromosomes Deck (51):
1

Describe the structure of a chromosome (after replication).

Two genetically identical sister chromatids

Joined at a centromere

Telomeres at the end of each chromatid

Heterochromatic and euchromatic sections

2

What is euchromatin?

Lightly packed form of chromatin

3

What is heterochromatin?

Tightly packed form of chromatin

4

Which form of chromatin does DNA transcription take place on?

Euchromatin

Loosely packed - allows enzymes n shit in

5

What are telomeres?

Long section of repeating base sequences at the ends of chromosomes

In mitosis, sections are cut off the 3' to 5' strand of DNA for reasons I can't be bothered typing (end replication problem)

Telomeres protect useful DNA being cut off

6

Describe the phases of mitotic cell cycle.

G1 - cell grows

S - DNA replicates

G2 - Cell prepares to divide

M - mitosis - cell division

7

List the stages of mitosis.

Prophase
Metaphase
Anaphase
Telophase
Cytokenesis

(interphase)

8

What happens in Prophase?

Chromosomes condense

Nuclear membrane

Spindle fibres form from the centriole

9

What happens in metaphase?

Chromosomes align on equator of cell

Chromosomes attach to centrioles via spindle fibre

Maximum condensation of chromosomes

10

What happens in anaphase?

Sister chromatids split apart (centromere splits)

Sister chromatids move to opposite poles of the cell, along the spindle fibre

11

What happens in telophase?

New nuclear membranes form

12

What happens in cytokinesis?

Cytoplasm splits and two new daughter cells are formed

Cells are diploid, have 46 chromsomes and are genetically identical

13

What is the name given to repetitive sequences of DNA, like the ones found in centromeres and telomeres?

Satellite DNA

14

What is the kinetochore?

A complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach

One forms per sister chromatid

15

What are the 2 types of tandemly repeated DNA sequences?

Satellite and minisatellite

16

What are the types of repeated interspersed DNA sequences?

SINEs - short interspersed nuclear elements

LINEs - long interspersed nuclear elements

17

Describe the properties and functions of histones.

Positively charged proteins

8 histones come together to form a core

DNA wraps around histone cores to form nucleosomes

Looks like beads on a string

18

Describe the levels of structure of chromatin.

1) DNA chain

2) Nucleosome

3) Chromatin fibre (further wrapping of nucleosomes)

4) Fibre scaffold complex

5) Chromosome

19

Why is it important that histone proteins are positively charged?

DNA is negatively charged

Neutralised by histones and holds it together

20

What are the 3 types of chromosome, and what are their differences?

Metacentric - p arm similar size to q arm

Submetacentric - p < q

Acrocentric - p << q (p has no functional DNA)

21

What type of cell in the body can not be used for chromosome analysis and why?

Red blood cells

No nucleus so no chromosomes

22

Describe the process of chromosome analysis.

Blood taken and RBC's seperated off

Add culture medium to white cell suspension

Incubate 3 days at 37 degrees

Add colchicine

Separate off white cells

Add hypotonic saline

Fix cells

Drop cells onto slide and stain

Analysis and photograph to produce karyotype

23

What does staining of chromosomes show?

G-bands

24

Why would you use fluorescent in sutu hybridisation (FISH)?

Highlight specific genes or specific parts of genes

25

What are the different types of FISH probes?

Unique sequence probes

Centromeric probes

Telomeric probes

Whole chromosome probes

26

Which type of FISH probe is good for determining chromosome number?

Centromeric probes

27

What type of cells undergo meiosis?

Germ cells

Diploid cells (in ovaries and testes) form haploid cells

28

How does meiosis create genetic diversity?

Crossing over (re-combination)

Independent assortment

29

What is Oogenesis?

Process of egg formation

30

Spermatogenesis is the process of?

Sperm formation

31

Out of sperm and eggs, which has more chance of mutation?

Sperm

More cell divisions so more chance of mutation

32

In females, ovulation takes place at birth.

Meiosis normally produces 4 daughter cells, but how is this different in women?

Meiosis II produces 1 Ootid and 3 polar bodies

Ootid differentiates into an egg

Polar bodies are degraded

33

What organelle is maternally inherited only?

Mitochondria (+ their DNA)

34

What are 3 types of chromosomal abnormalities?

Numerical

Structural

Mutational

35

What type of abnormality is associated with down's, turner's and patau syndromes?

Numerical abnormality

Aneuploidy - wrong number of chromosomes

Down's = Extra 21
Edward's = Extra 18
Patau = Extra 13

36

What gives rise to numerical chromosomal abnormalities?

Non-disjunction during meiosis

37

Trisomy is more commonly caused by what sex?

Maternal

38

Give some examples of sex chromosomes aneuploidy syndromes.

Turner syndrome - 45, X

Klinefelter syndrome - 47, XXY

39

What are the types of structural abnormalities of chromsomes?

Translocations

Deletions

Inversions

Insertions

40

What are the two types of translocations?

Robertsonian - fusion of two acrocentric chromosomes, with loss of the short arms (p arms)

Reciprocal - breaks of 2 chromosomes with the formation of 2 new chromosomes from these

41

How can reciprocal translocations be balanced or unbalanced?

If chromosome A and chromosome B translocate, part of B is on A and vice versa

If A and B end up in the same cell after meiosis, then the DNA compliment is the same, and the outcome will most likely be fine

If A and B end up in different daughter cells, then the zygotes will have an unbalanced amount of A or B

Partial trisomy + partial monosomy

42

What is the difference between terminal and interstitial deletion?

Terminal = deletion at ends

Interstitial = deletion in the actual chromosome (not the end)

43

What are the two types of inversion, and are the balanced/unbalanced?

Paracentric and pericentric

Paracentric = inversion in chromosome not involving centromere

Pericentric = inverted section contains centromere

Balanced rearrangement

44

What are the 2 types of genetic mutation?

Germline or somatic

45

What are the different types of coding mutations?

Silent - Base change with no effect on coded AA

Missense - Base change causing AA change

Nonsense - Base change causing stop codon

Frameshift - deletion/insertion of a base - codons after are read out of frame

46

What is the difference between transitions and transversions?

Transitions = purine to purine or pyrim. to pyrim.

Transversions = purine to pyrim. or pyrim. to purine

47

What are the ways that we can detect mutations?

PCR - Polymerase chain reactions

Gel electrophoresis

RFLP - Restriction fragment length polymorphism analysis

ARMS - Amplification refractory mutation system

DNA sequencing

48

Which mutation detection technique involves heating and DNA sample then adding nucleotides, repeatedly?

PCR

49

In gel electrophoresis, different DNA fragments are separated based on what feature?

Size

DNA fragment 'bands' can be compared to other bands to detect differences/mutations to the bands formed from non-mutated DNA fragments (controls)

50

What technique is most sensitive/accurate for detecting mutations?

DNA sequencing

51

What is the only lab procedure for DNA analysis that doesn't involve using an electric field to separate DNA fragments?

PCR