Chromosomes Flashcards by Michael Alcorn

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

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What is euchromatin?

Lightly packed form of chromatin

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What is heterochromatin?

Tightly packed form of chromatin

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Which form of chromatin does DNA transcription take place on?

Euchromatin

Loosely packed - allows enzymes n shit in

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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

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Describe the phases of mitotic cell cycle.

G1 - cell grows

S - DNA replicates

G2 - Cell prepares to divide

M - mitosis - cell division

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List the stages of mitosis.

Prophase 
Metaphase
Anaphase
Telophase
Cytokenesis

(interphase)

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What happens in Prophase?

Chromosomes condense

Nuclear membrane

Spindle fibres form from the centriole

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What happens in metaphase?

Chromosomes align on equator of cell

Chromosomes attach to centrioles via spindle fibre

Maximum condensation of chromosomes

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What happens in anaphase?

Sister chromatids split apart (centromere splits)

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

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What happens in telophase?

New nuclear membranes form

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What happens in cytokinesis?

Cytoplasm splits and two new daughter cells are formed

Cells are diploid, have 46 chromsomes and are genetically identical

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

Satellite DNA

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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

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What are the 2 types of tandemly repeated DNA sequences?

Satellite and minisatellite

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What are the types of repeated interspersed DNA sequences?

SINEs - short interspersed nuclear elements

LINEs - long interspersed nuclear elements

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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

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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

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Why is it important that histone proteins are positively charged?

DNA is negatively charged

Neutralised by histones and holds it together

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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 &laquo_space;q (p has no functional DNA)

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

Red blood cells

No nucleus so no chromosomes

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

What does staining of chromosomes show?

G-bands

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

Highlight specific genes or specific parts of genes

What are the different types of FISH probes?

Unique sequence probes Centromeric probes Telomeric probes Whole chromosome probes

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

Centromeric probes

What type of cells undergo meiosis?

Germ cells Diploid cells (in ovaries and testes) form haploid cells

How does meiosis create genetic diversity?

Crossing over (re-combination) Independent assortment

What is Oogenesis?

Process of egg formation

Spermatogenesis is the process of?

Sperm formation

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

Sperm More cell divisions so more chance of mutation

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

What organelle is maternally inherited only?

Mitochondria (+ their DNA)

What are 3 types of chromosomal abnormalities?

Numerical Structural Mutational

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 ```

What gives rise to numerical chromosomal abnormalities?

Non-disjunction during meiosis

Trisomy is more commonly caused by what sex?

Maternal

Give some examples of sex chromosomes aneuploidy syndromes.

Turner syndrome - 45, X Klinefelter syndrome - 47, XXY

What are the types of structural abnormalities of chromsomes?

Translocations Deletions Inversions Insertions

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

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

What is the difference between terminal and interstitial deletion?

Terminal = deletion at ends Interstitial = deletion in the actual chromosome (not the end)

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

What are the 2 types of genetic mutation?

Germline or somatic

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

What is the difference between transitions and transversions?

Transitions = purine to purine or pyrim. to pyrim. Transversions = purine to pyrim. or pyrim. to purine

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

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

PCR

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)

What technique is most sensitive/accurate for detecting mutations?

DNA sequencing

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

PCR