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Genetics Lab (lecture) Flashcards

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1
Q

What is genetic variation?

A

genetic difference between individual within or different populations

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2
Q

What does variation cause?

A

different phenotypic characteristics (traits)

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3
Q

How can variation occur?

A

-On many scales- from gross alterations in human karyotype to a single nucleotide changes

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4
Q

What is a human karyotype?

A

an individuals collection of chromosome

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5
Q

what can variations be divided into?

A
  • Polymorphisms

- Disease causing mutation

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6
Q

What is a polymorphism?

A

If variations are found frequently in a population

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7
Q

What is a disease causing mutation?

A

detrimental in health

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8
Q

What IS variation?

A

driving force of evolution by natural selection therefore allowing us to adapt to other environments
-Genetic mutation is random hence some phenotypes could be either beneficial (over the others) or damaging to organisms.

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9
Q

What is an allele?

A
  • One or more gene given at a point (locus) on a chromosome.
  • Each allele in each person probably has a slightly different genetic code than the other one
  • May occur in pairs or multiple.
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10
Q

How can a mutation occur in a. allele?

A

at each locus point.

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11
Q

What are the different types of mutation?

A
  • Point mutations
  • Frameshift mutatations
  • Contiguous repeats ( repeat of 2 or 3 nucleotides)
  • CNV (Copy number variaiton)- genes multiplied or deleted
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12
Q

What is point mutation ?

A

.A point mutation is when a single base pair ( in a triplet/codon) is altered
which occurs by a simple mistake during DNA replication in meiosis
. sometimes such mutations can have severe consequences i.e.sickle cell anaemia

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13
Q

What is a frameshift mutation?

A

A frameshift mutation is a genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read.
. this is more serious

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14
Q

What happens when you assume a point mutation happens in an exon?

A

You can get:
1- Silent mutation- result in no change in amino acid sequence–> synonymous mutation
2. Missense- change in a sequence
3. Nonsense- premature stop codon

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15
Q

What is an exon?

A

expressed region of the genome

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16
Q

How can you Get a change in a nucleotide sequence but not an amino acid sequence?

A

Via the Silent mutation

  • As it may have created another codon which codes for the exact same amino acid
  • e.g. originally FOR Alanine (GCU) , and could have replaced ‘U’ with a ‘C’ so (GCC) however that codon codes still for Alanine.
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17
Q

What is a silent mutation?

A

a mutation in the nucleotide sequence which results in no change in the amino acid sequence.

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18
Q

What are the non synonymous mutations?

A
  • Missense

- Nonsense

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19
Q

What is a nonsense mutation?

A
  • Some nucleotide sequences (codon/triplet) don’t code for an amino acid however code for a signal to stop the process of translation.
  • occurs at end of a.a chain- protein made the sequence is coding for.
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20
Q

What is a missense mutation?

A
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21
Q

What does each a.a. acid have?

A

a specific characteristic to them

  • specific chemical propertires
  • e.g could have slightly positive, negative charge or neutral
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22
Q

What is a conservative missense mutation?

A

If the amino acid sequence is changed but retains biochemical properties- for e.g.- a.a is slightly changed, won’t have much effect on the folding of the a.a chain- however the protein made is able to perform the function of the original non-mutated protein or it may have no effect whatsoever?

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23
Q

What is a non-conservative missense mutation?

A
  • If the amino acid sequence is changed but changes biochemical properties
  • Massive effect of. how that a.a. chain folds into that protein - and so effects the function of the protein.
  • A signifcant effect on ultimate phenotype - could lead to a different trait or to a disease
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24
Q

What are insertions/deletions caused by?

A

-by frameshift mutation

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25
What is the effect caused by insertions/deletion?
- Changes how the following amino acids are read and coded for. - Altered reading frame
26
What does the altered reading frame cause?
a frame shift mutation - when the insertion or deletion changes down stream reading of codons
27
What happens if you have an insertion or deletion of 3 nucleotides long?
- That is a non frame shift. | - Lead to either. complete deletion or inserion
28
What are the polymorphisims?
- Variants found in within more than 1% of the general population - More than 1 in 100 people share that genetic mutation - Found in such high prevalance within population, less likely to cause a genetic disease - Changes in genetic code for the disease won't get passed on- less likely recurrence of reproduction - Selection pressure of people not mating with people of a genetic mutation. - Cause variation in phenotype
29
What can polymorphisms affect?
-Disease predisposition, progression, or drug response when combined with other genetic and environmental factors (disease risk factor) -Good e.g when you get autoimmune disease -
30
What are the 3 common types of polymorphisms?
1. Single nucleotide polymorphism (SNPs) 2. Small insertion/deletions (Indels) 3. Large-scale copy number polymorphisms ( CNPs or CNVs)- whole changes in gene number
31
What are SNPs?
- is a point mutation
32
How many nucleotides do we have in every nucleus?
6billion | -We differ one from another at approx 1:1000 nucleotides
33
What is the percentage of human DNA being identical between individuals?
99.9%
34
How much % do we differ of our genetic material?
0. 1% - of the 0.1% - 80% of those differences are due to point mutations - Due to SNP - most common
35
What are indels?
- Insertions or deletions of nucleotide sequences of 2 -10,000 base pairs- can have large scale changes / regions - 2nd most common polymorphism
36
How is polymorphism different from a mutation leading to a specific disease?
- Purely the prevalence in the general population | - if the mutation is found in less than 1% of the population it is referred to as a MUTATION
37
What are disease causing mutations?
- if the mutations lead to a protein with loss of function or aberrant expression of a protein. - These disease causing mutations lead to different functioning protein after. - They are often in exons.
38
What are the disease causing mutations referred to as?
- Point mutations - frameshift mutations - inversions- flip around - copy number variations
39
What are large changes in genetic material?
Chromosomal disorders | -Rare but significant phenotypical changes
40
What happens in chromosomal disorders?
- Complete loss or gain of chromosome- non-disjunction - Lead to rearrangement- Incorrect crossing over - loss of part of chromosome
41
What are 3 regions of a chromosome?
-Centromere -2 stretches of genetic material : P arm- short arm sticking out from centromere And Q arm - long arm sticking out from centromere
42
How is DNA coiled up into these region ?
Tightly packed (being dense) leads to puckering where centromere is.
43
What happens when you stain the chromosomes?
-Banding patterns- diff bands and sub bands
44
What happens when you uncoil a chromosome?
- It is Tightly packed loops of DNA - its DNA wrapped around a nucleosome- which is formed from a protein called histone - -Un peel DNA strand from histone nucleosome- you see classic DNA double helix
45
How many histone molecules do you have?
8 molecules- made up of 4 different types | Histone H2A, H2B, H3 , H4
46
What are the histones?
-proteins that condense/coil and structure the DNA of eukaryotic cell nuclei into units called nucleosomes
47
What is the histone octamer?
-Consists of 2 copies of each histone protein
48
How is the nucleosome core formed?
-2 H2A-H2B dimers (bound together) and 1 H3-H4 tether (2H3 and 2H4)
49
What is the nucleosome core structure?
8 histone molecules in the centre | -DNA chain coils around octamer time and is anchored by another histone molecule H1.
50
How can we tell the gross structure of the chromosome?
- Using a Karyogram- referred to as the Karyotype: look at structure and number of chromosomes, banding pattern of chromosome and count ,to check position of centromere to check for addition or deletion. - See sex chromosome- identify gender- any addition and deletion of chromosomes
51
What is the process of a Karyogram?
- Take cell sample - Culture in dish - Induce cell to go through mitosis - Arrest cell division during METAPHASE - Extract chromosomes from a single cell- during metaphase - once chromatins condensed down - Stain with Giemsa- to see the different density regions - Then align the autosome pairs up and put in chromosome order - Put in length order Compare - Chromosome count - Centrosome position: length of P ARM and Q arm - Banding Pattern - Sex chromosomes
52
What is the 1st chromosome rearrangements ?
-Balanced reciprocal Translocations- During normal process of Meiosis 1 you get a cross over- normal- deriving force of evoultion- allows for more possible genetic variations than mistakes in DNA copying (where DNA polymerase goes wrong
53
What is the 2nd chromosome rearrangement ?
- Centric fusion- Robertsonian - Chromosomes don't line correctly within the tetrad- when crossing over occurs - may have Q arm of one chromosome being crossed over and replaced for the P arm of the other chromosome within that tetrad - End up with one chromosome with double amount of genetic material from Q arm to the P arm - Have 2 genes from every gene that would be found on just Q arm - Leads to massive change in genetic material- affect on phenotype of person - Essentially creating a person that has 3 copies of a lot of the genes- the phenotypes that come out of this will be similar to trisomy. - Lead to down syndrome phenotype- robersonian translocation of the Q arm on chromosome 21
54
What is the 3rd chromomsal rearrangements?
- Isochromosome- during separation of sister chromaitds- instead of having aplane of splitting down the middle off the chromosome- sometimes microtubules pull and split the sister chromatids incorrectly - Then when they separate one sister has 2 P arms and other sister has 2 Q arms - Leads to doubling up of the genetic material of the same of the chromosome
55
What is the 4th chromosomal rearrangements?
Deletion/Insertion- when crossing over doesn't occur properly and some fragments are lost rather than being inserted in other chromosomes - Can occur during replication (interphase)- DNA polymerase may not have copied the genetic material or double up a large section of material
56
What is the 5the chromosomal rearrangement?
Inversions- can have regions of alleles which are inverted within the chromosome. This can either be around the centromere (pericentric)or within one of.the arms (paracentric)
57
What is the 6th chromosomal rearrangement?
-Ring chromosome- genetic material fragmented off from end of chromosme- make molecule unstable- so stabilises itself by forming a ring
58
What is subject to non-disjunction?
sex chromosomes e. g females with only one X chromosome are suffering from turners syndrome - the possession of XXX chromosomes is known as meta female syndrome - XXY in males- kleinfelters syndrome
59
What is downsyndrome?
- Common chromosomal disorders - 1 in 800 people - 95% caused by trisomy of chromosome 21 - Not all down syndrome caused by chromosome 21 - 5% caused by Robertsonian mutation- 2 Q arms on one chromosomes - leads to phenotype of having trisomy chromosome - 40% develop cardiac problems - 10-20 increase risk leukaemia - more than 40 develop neuropathology - Autoimmune disease predisposition - Estropia and hyperopia
60
explain chromosome structure ?
1. at the simplest level , chromatin is a double - stranded helical structure of DNA 2. DNA is complexed with histones to form nucleosome 3. each nucleosome consists of eight histone proteins which wrap the DNA 1.65 times 4. a chromosome consists of a nucleosome plus the H1 histone

Biology Lab (5 decks)

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