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BMS 500 - Human Genetics > WK 2 > Flashcards

WK 2 Flashcards

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Biology 101 flashcards
1
Q

The law of segregation

A

Traits are controlled by alleles (forms of a gene at a specific locus), which segregate during meiosis (gamete formation; each gamete carries only one allele of each gene) and re-form randomly in a fertilized zygote.

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2
Q

The law of independent assortment

A

Alleles controlling traits segregate independently during meiosis.
Does not hold true for linked genes.

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3
Q

Chromosomes are composed of

A

chromatin which are histones (proteins) and DNA

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4
Q

Core histones

A

8 proteins.
2 copies of each type of histone.

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5
Q

Chromatin packing: interphase vs. mitosis

A

Interphase:
- ‘uncondensed’ chromatin
- cooked spaghetti all tangled

Mitosis:
- extremely highly condensed chromatin
- especially in metaphase

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6
Q

Cycle of condensation and decondensation as a chromosome proceeds through the cell cycle.

A

Relaxed in interphase
Starts compacting in prophase
Condensed in metaphase

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7
Q

Each chromosome occupies a specific spot called

A

a chromosome territory.

Chromosomes dense with genes seem to be closer to the center of the nucleus.

Bigger chromosomes with lower gene density are around the periphery.

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8
Q

Nucleosome

A

DNA wrapped around eight core histone proteins: two each of histones H2A, H2B, H3, and H4. Histone H1 is bound to linker DNAimmediately outside the nucleosome and keeps in place the DNA wrapped round the nucleosome. Core histones have an extensive α-helical structure and a protruding N-terminal tail.

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9
Q

‘The Histone Code’ Hypothesis

A

A hypothesis which states that DNA transcription is largely regulated by post-translational modifications to histones proteins.

Most of gene expression is modified by histone tails.

N terminal tail has post translational modifications that determine what happens to the structure and function of this DNA.
- These changes can result in phenotypic changes without changing the genotype.

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10
Q

Epi genetic regulation

A

change the phenotype without changing the genotype

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11
Q

histone proteins

A

1 of H1, and 2 of the rest: H2A, H2B, H3, and H4

H2A – have diff types of H2A histones
- X
- Z
- Etc

These diff members have diff AA sequences

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12
Q

H2AX

A

involved in DNA damage repair

Some areas that are more prone to DNA damage have more

When there is DNA damage, it (H2AX) gets phosphorylated and that signals DNA repair machinery to come to the area and do repair

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13
Q

Acetylation

A

acetyl group added (- charge) which causes the DNA to open up in that region

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14
Q

Methylation

A

methyl group added

Could signal down regulation or up regulation of gene expression

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15
Q

Ubiquitination

A

a signal for degradation

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16
Q

Interphase chromatin types

A

euchromatin and heterochromatin

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17
Q

Euchromatin

A

“open chromatin”; lightly packed; often under active transcription; weak binding of H1; in humans, 90% of chromatin in interphase cells is euchromatin

Accessible and active – gene expression happening

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18
Q

Heterochromatin

A

“condensed chromatin”; tightly packed; less accessible for transcription; tight binding of H1

No gene expression happening

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19
Q

Transmission electron microscopy

A

Electrons go through the sample

How many electrons = how dense the sample is

Less dense = more electrons go through = lighter image

Less dense = euchromatin

20
Q

Two types of heterochromatin

A

constitutive and facultative

21
Q

Constitutive heterochromatin

A

most of the heterochromatin in cells; permanently, irreversibly condensed; associated with gene-poor DNA and highly-repetitive DNA sequences (centromeres, telomeres, much of the Y chromosome); genetically inactive in somatic cells; if through some chromosome rearrangement an actively expressed gene is transposed from a euchromatic region to a heterochromatic region, it is silenced.

Dna Not expressed

Packed and tucked away

Has roles but no gene expression

22
Q

Facultative heterochromatin

A

condensed structure that can be reversed(decondensed) and can be rich in genes; in female somatic cells one of the two X chromosomes is highly condensed – X-inactivation.

23
Q

X-inactivation

A

Random process that happens early in female development.

Within the first week of embryogenesis, one or the other X is chosen at random to become the future inactive X.

That X then becomes the inactive X (Xi) in that cell and its progeny and forms the Barr body in interphase nuclei. The resulting female embryo is a clonal mosaic of two epigenetically determined cell types: one expresses alleles from the maternal X, whereas the other expresses alleles from the paternal X.

Can have skewed X inactivation.
- Instead of 50-50, have extreme numbers

An example of epigenetics regulation

Long non functional RNA that is non coding which starts coating the chromosome and signals and creates compaction and silencing of the chromosome

Some genes can escape this and complicate things

Epigenetics modifications can silence chunks or whole chromosome

24
Q

Cytogenetics

A

The study of the architecture of chromosomes in cells and their role in heredity.

Involves testing samples of tissue, blood, or bone marrow in a laboratory to look for changes in chromosomes, including broken, missing,rearranged, or extra chromosomes. In cytogenetics, we are mostly dealing with condensed chromosomes (it is hard to analyze decondensed chromosomes)

Used a lot in clinical labs, used to determine a diagnosis.

25
Q

Karyotype

A

(chromosome chart): major clinical tool that describes the chromosome count of an organism, what chromosomes look like under a light microscope, according to their length, the position of the centromeres, banding pattern, differences between the sex chromosomes, and any other physical characteristics.

26
Q

Conventional cytogenetics

A

karyotyping/chromosome banding - Preparing samples and looking at them under a microscope

27
Q

Molecular cytogenetics

A

Molecular cytogenetics uses probes:
Fluorescence in situ hybridization (FISH)
Comparative genomic hybridization (CGH)

28
Q

Centromere

A

Where the spindles attach and pull apart in anaphase

29
Q

Telomeres

A

at each end

They get degraded over time to prevent the actual DNA from being degraded

They protect the chromosome

They are repetitive sequences

30
Q

short arm

A

p arm

31
Q

long arm

A

q arm

32
Q

Metacentric

A

Short and long arm are same length

33
Q

Submetacentric

A

Short arm is short and long arm is long

34
Q

Acrocentric

A

Short arm is very short and long arm is very long

35
Q

Telocentric

A

No short arm

Telomere at the top, then centromere, then long arm and telomere

Not found in humans unless there’s a structural mutation that happens

Found in some animals

36
Q

How to obtain a chromosome spread / karyotype

A

Grow cells in culture
Add colchicine/colcemid
Swell and fix cells
Spread cells on slide
Stain and image

37
Q

Karyogram

A

Chromosomes arranged by size (largest to smallest) in pairs, and then sex chromosomes last

38
Q

Giemsa or G-banding

A

most common banding method

Giemsa binds preferentially binds to A and T (AT rich residues)

A and T are gene poor, non coding regions

Dark stain on A and T

Light bands in euchromatic regions (C and G)

Used to see if you’re missing parts of chromosomes

39
Q

Reverse or R-banding

A

shows the reverse banding pattern of Giemsa (i.e., reversal of light and dark G-bands). The numbering of the bands is identical with both binding methods. Heat denaturation followed by Giemsa staining.

The opposite staining pattern of G banding

40
Q

C-banding

A

centromeric and pericentromeric DNA are composed of repetitive satellite DNA, which are easily visualized using constitutive heterochromatin (C-banding) methods.

Used to find where the centromere is

To see if something is wrong with centromeres

41
Q

silver-based NOR staining

A

short arms of the acrocentric chromosomes house the ribosomal RNA gene clusters in the nucleolar organizing regions (NORs), which form the nucleolus of the cell.

Used to find NOR regions

Silver staining – detect proteins that are relating to the NOR regions

These regions form the nucleolus

42
Q

T-banding

A

telomeres are composed of (TTAGGG)n mini-satellite repeats that staindarkly with T-banding.

Used to find where the telomere is

To see if something wrong with telomeres

43
Q

Q-banding

A

Same as G but instead you use something fluorescent

Can detect smaller regions and amount and get better staining and results than G banding

Most used technique

DAPI – blue fluorescent stain that binds to dna and used to detect dna in micrographs

44
Q

NOR

A

nucleolar organizing region

leads to formation of nucleolus

45
Q

Idiogram

A

Schematic diagram that provides a pictorial reference point that is useful for locating the positions of individual genes on chromosomes, and for identifying various abnormalities associated with a range of chromosomal disorders.
- Turn a karyogram into an ideogram
- Centromere is shown in dark lines
- Grey is repetitive dna

46
Q

How many bp or genes in one band?

A

Bands can contain millions of basepairs, and many genes (up to hundreds of genes).
- (one band ≠ one gene) - simply an area of genes
- Each band is numbers starting at the centromere and becomes larger as it go towards the telomere

47
Q

CFTR gene = 7q31.2 (what does the location tell you?)

A

CFTR - Cystic Fibrosis Transmembrane Conductance Regulator
- Chromosome 7
- Arm q (long arm) Region 3
- Band 1
- Sub-band 2
- = 7q31.2

BMS 500 - Human Genetics (4 decks)

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