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HHP > Genetics 1 > Flashcards

Genetics 1 Flashcards

1
Q

what does hereditary / inheritance refer to

A

what is happening to traits passed on or within multiple generations of a given family

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2
Q

what is the best way to follow inheritance patterns

A

family pedigree analysis

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3
Q

family pedigree standardised symbols:

what do the roman numerals down lhs mean

A

generation number (ie I will be at the top row, fourth row is 4th generation so IV etc)

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4
Q

family pedigree standardised symbols:

what do diagonal lines across a shape mean

A

individual has already died (so we don’t know if they’re affected or not)

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5
Q

family pedigree standardised symbols:

what do circles represent

A

females

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6
Q

family pedigree standardised symbols:

what do squares represent

A

males

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7
Q

family pedigree standardised symbols:

what does a plain circle or square represent

A

healthy individuals

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8
Q

family pedigree standardised symbols:

what does a filled in (ie in black) circle or square represent

A

diseased individuals

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9
Q

family pedigree standardised symbols:

what do dots or vertical stripes inside shapes / half shaded shapes represent

A

carriers of the disease (carry the defective gene but dont have the disease)

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10
Q

family pedigree standardised symbols:

how are twins symbolised

A

lines from parents make a triangle formation

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11
Q

family pedigree standardised symbols:

how are IDENTICAL twins symbolised

A

same triangle BUT they are also joined by a horizontal line between them

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12
Q

in what 5 ways can genetic information be passed from one generation to the next

A

1) human karyotype
2) chromosome structure
3) double helix
4) nucleobases and nucleotides
5) the genetic code

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13
Q

human karyotype:

what do chromosomes carry in eukaryotic cells

A

genetic information

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14
Q

human karyotype:

what is the normal karyotype for 1) males and 2) females

A

1) XY

2) XX

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15
Q

human karyotype:

how is genetic information passed on via this route

A

one chromosome in each of the 23 pairs is derived from mother and other from father

the dna of every chromosome records info that can be translated by the cells

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16
Q

chromosome structure:

during what stage of cell growth can we best observe condesnsed tightly packed DNA chromosomes

A

metaphase

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17
Q

chromosome structure:

what are the 3 steps of packing unwound structure of dna double helix into densely condensed chromosomes

A

1) dna wound around histone proteins (octamer) forming nucleosome
2) many nucleosomes look like ‘beads on a string’ = this is chromatin
3) regions of chromatin molecule interact and form chromatin fibres which are coiled and condensed to form chromosomes

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18
Q

the double helix:

which 2 scientists first described the double helix

A

watson + krick

base pairs are called watson-crick base pairs

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19
Q

the double helix:

what does it consist of

A

2 anti-parallel polynucleotide chains of specific chemical composition, held together by hydrogen bonding between pairs of nucleobases

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20
Q

the double helix:

what do nucleobases make up

A

the 4 letter code which encodes the genetic information

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21
Q

nucleobases and nucleotides:

what are the 2 types of nucleobases and what are they grouped based on

A

1) purine
2) pyrimidines
3) chemical structure

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22
Q

nucleobases and nucleotides:

list the purine bases

A

adenine

guanine

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23
Q

nucleobases and nucleotides:

list the pyrimidine bases

A

cytosine
thymine
uracil

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24
Q

nucleobases and nucleotides:

what is the structure of a nucleotide

A

a deoxyribose sugar with 1 phosphate and 1 nucleobase attached to it

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25
Q

nucleobases and nucleotides:

how are single nucleotides with different bases linked together into 1 sequence

A

phosphate group forms bonds with 2 ribose sugars

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26
Q

nucleobases and nucleotides:

how is the double helix formed

A

2 strands of antiparallel sequences of nucleotides bind to each other through hydrogen bonding

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27
Q

nucleobases and nucleotides:

what is the hydrogen bond pairing between the bases

A

adenine and thymine (or uracil in rna) = 2 H bonds

guanine and cytosine = 3 H bonds

(forms backup bc same info encoded)

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28
Q

the genetic code:

what can letters of nucleobases encoded in DNA be translated into

A

proteins (ie Val = valine)

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29
Q

the genetic code:

what does a codon translation table show

A

how cells interpret free nucleobases as a signal for each amino acid AND where to start / stop reading sequences

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30
Q

the genetic code:

what does the genetic code being redundant mean

A

several triplet codons code for the same amino acid

mutations can be silent (where a triplet changes so genetic code changes but new triplet still codes for the same amino acid)

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31
Q

what is the basis of inherited disease

A

MUTAGENESIS

mutations are heritable permanent changes in dna base seq which allow new changes/disease to arise because they change information encoded

32
Q

list the 5 types of mutation

A

1) point
2) deletions / insertions
3) silent
4) missense
5) nonsense

33
Q

point mutations:

what are they

A

happen in one base / one base pair of double helix seq

change only 1 letter of code at given position

34
Q

point mutations:

what are the 2 types and what do they do

A

1) TRANSITION = where a purine base is substituted with another purine base OR pyrimidine substituted with another pyrimidine
2) TRANSVERSION = where a purine is substituted with a pyrimidine or vice versa

transition is more limited

35
Q

deletions / insertions:

what are these mutations characterised by

A

loss / gain of nucleotides

36
Q

deletions / insertions:

what may these mutations lead to…

A

FRAMESHIFT MUTATIONS (change how genetic code is read and affect all information encoded after the mutation because the cell applies a new triplet reading frame)

37
Q

silent mutations:

what are these

A

Usually point mutations changing nucleotide seq but not coded amino acid bc of redundancy of genetic code

38
Q

missense mutations:

explain these

A

point mutations in which a single nucleotide change results in different amino acid being encoded

39
Q

nonsense mutations:

what is this

A

codon usually coding for an amino acid is changed to a STOP CODON

40
Q

nonsense mutations:

what do they lead to

A

premature truncation of encoded proteins (because cell stops reading information prematurely and no more amino acids are added)

leading to a shortened protein

41
Q

give two general ways in which mutations may arise

A

1) dna replication fidelity (internal enzymes causing mutation)
2) mutagens (external stimuli)

42
Q

dna replication fidelity:

how may this arise

A

Enzyme carrying out replication is accurate in terms of reading + copying seq ensuring identical daughter cells

43
Q

dna replication fidelity:

how does DNA polymerase work

A

VERY LOW ERROR RATE

replicates by reading DNA seq in one strand, then inserting complementary nucleotides that can H bond giving a sequence corresponding perfectly to seq encoded in the other strand

44
Q

dna replication fidelity:

what function does dna polymerase have for if a nucleotide that DOES NOT H bond is encorporated

A

EXONUCLEASE FUNCTION

3’ to 5’ proofreading function

removes error allowing correct nucleotide to be encorporated

45
Q

mutagens:

what are the 2 types of mutagens

A

1) physical

2) chemical

46
Q

physical mutagens:

give 2 examples

A

1) ionising radiation

2) non-ionising radiation

47
Q

physical mutagens:

give examples of ionising radiation and explain how these lead to mutations

A

x-rays, gamma rays

causes strand breaks in dna or sugar/base destruction

48
Q

physical mutagens:

give examples of non-ionising radiation and explain how these lead to mutations

A

uv light

causes NEW chemical bonds such as pyrimidine dimers

49
Q

physical mutagens:

what are pyrimidine dimers

A

molecular lesions

form during photochemical reactions when covalent bonds form between neighbouring thymine / cyotsine bases in the same strand

50
Q

chemical mutagens:

give 3 examples

A

1) base analogues
2) nitrous acid
3) alkylating agents

51
Q

chemical mutagens:

what are base analogues

A

derivatives of normal bases (look similar to nucleobases) so are wrongly incorporated by dna polymerase

52
Q

chemical mutagens:

how can base analogues cause mutation

A

cause altered base pairing

53
Q

chemical mutagens:

how does nitrous acid cause mutations

A

carries out deamination reaction on cytosine nucleobases changing it to uracil = causes GC base pairing to AC base pairing transitions

54
Q

chemical mutagens:

give an example of an alkylating agent and explain how they cause mutations

A

methylmethane sulfonate

Cause lesions that result in error prone repair, increasing error rate of dna polymerase

55
Q

mutagens:

for safety reasons what is done to mutagenic chemicals

A

labelled with specific pictograms / info detailing their mutagenic effects

56
Q

define allele

A

different forms of the same gene

we have 2 copies of each chromosome so 2 of each gene, gene may exist in 1+ form as different varieties of same genes

57
Q

define dominant

A

a gene that, if present, expresses a certain characteristic

doesn’t matter what info on other allele is

58
Q

define recessive:

A

gene whose character is only expressed in absence of a dominant gene

natural version of gene has to be changed on both chromosomes for recessive characteristic to cause a phenotype

59
Q

define phenotype

A

visible appearance of a change in the genetic info

displayed / observable characteristics

60
Q

define genotype

A

encompasses genetic components of info in an individual

61
Q

what are diploid genomes

A

2 copies of each chromosome

62
Q

what is a recessive lethal allele

A

pair of identical alleles
only one chromosome is affected SO individual is healthy as the healthy gene in the other chromosome is dominant so expressed
can code for dominant or recessive traits but ONLY fatal (cause death) in homozygous condition

63
Q

what is the probability of offspring being a carrier when a carrier of a recessive lethal allele mates with a non affected individual

A

50% of offspring will be carriers but are ALL viable as non-mutated copy is dominant

64
Q

what are the probabilities when both parents carry a recessive lethal allele

A

1) 50% healthy carriers
2) 25% healthy, non-carriers
3) 25% affected as carry 2 copies of mutated recessive allele which will be lethal (will kill)

SO OVERALL
75% healthy and 25% affected (affected die)

65
Q

what is the probability of offspring being affected in

a) autosomal dominant inheritance where one parent is affected and one is unaffected
b) in autosomal recessive patterns of inheritance

A

a) 50%

b) 75%

66
Q

what are single gene (MONOGENIC) disorders

give the 3 types / patterns of inheritance these may be

A

traceable to a single mutated gene

1) autosomal recessive
2) autosomal dominant
3) sex-linked

67
Q

give 2 examples of autosomal recessive inheritance

A

cystic fibrosis = CFTR gene is affected

sickle cell disease = beta-globin gene is affected

these mutations arise on 1 of chromosomes 1-22 NOT on the sex chromosomes X and Y

68
Q

give an example of autosomal dominant disorder

A

huntingtons

69
Q

explain sex linked disorders and give an example

A

encoded on one of sex chromosomes (usually X as it contains more info)

amelogenesis imperfecta which affects tooth enamel

70
Q

what are major monogenic recessive disorders

A

monogenic disease occuring at a given frequency in a population depending on size, health, external factors, genetic history

71
Q

give 3 examples of major monogenic recessive disorders

A

1) cystic fibrosis
2) sickle cell anaemia
3) thallassaemias

72
Q

what does cystic fibrosis cause and how many north europeans does it affect

A

recurrent lung infections

1/2000

73
Q

what does sickle cell anaemia cause and how many africans does it affect

A

anaemia

1/50 where malaria is endemic

74
Q

why are frequencies of sickle cell anaemia carriers / affected HIGHER in areas where malaria is endemic

A

sickle cell anaemia give a selective advantage in regions where higher rates of malaria infection by giving some protective advantage

75
Q

what do thallassaemias cause and how many asians + mediterraneans does it affect

A

anaemia

1/50

76
Q

how does selective advantage explain higher frequency in a population

A

bc of recessive nature individuals that are carriers reproduce at higher rate

HHP (10 decks)

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