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GENETICS 1 Flashcards

1
Q

what is a phenotype

A

this is the outward and physical manifestation of an organism

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2
Q

what is a genotype

A

this is the full hereditary information of an organism even if not expressed .

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3
Q

what is the relationship between DNA structure an d function

A

DNA is transcribed into mRNA and then translated into proteins in the ribosome .

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4
Q

what is the structure of a DNA

A

made up of a pentose sugar , phosphate group and a nitrogenous base .

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5
Q

what is a nucleoside

A

a base and a pentose sugar

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6
Q

bonds involved in a DNA molecule

A

there is hydrogen bonds that are formed between the nitrogenous bases.

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7
Q

what are purines

A

they are adenine and guanine

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8
Q

what are pyrimidines

A

they are thymine , cytosine and uracil in the RNA .

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9
Q

complementary base pairing the number of bonds that are formed

A

3 bonds for cytosine and guanine
2 bonds for adenine and thymine

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10
Q

the largest organelle in animal cells

A

the nucleus which contains the DNA

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11
Q

site for DNA replication

A

nucleus

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12
Q

site for DNA transcription

A

nucleolus

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13
Q

what are chromosomes

A

they are wound DNA that are packed together into a thread like structure.

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14
Q

length of the DNA

A

2m

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15
Q

what are the parts of a chromosome

A

the two sister chromatids that are joined together by the centromere.

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16
Q

how many chromosomes are present in a human cell

A

humans have 23 pairs of chromosomes with 22 pairs being autosomal while 1 pair the 23rd being sex chromosome

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17
Q

how does the DNA achieve the structure to be able to be packaged into a chromosome.?

A

they are tightly wound on histone proteins to form a nucleosome

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18
Q

what is a nucleosome

A

DNA that is wound around a histone protein.

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19
Q

what does a nucleosome comprise of

A

comprises of eight histone proteins around which the DNA wraps 1.65 times

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20
Q

chromatin

A

mixture of DNA ,(histone) proteins and RNA which package within the nucleus.

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21
Q

heterochromatin

A

the condensed regions of the chromatin

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22
Q

euchromatin

A

the extended form of the chromatin that is exposed and less wound

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23
Q

process of DNA transcription and replication

A

1.both require the unzipping and closure of the DNA helix structure this is done by the enzyme ligase and the enzyme helicase.
2. the histone wrapping at the nucleosome has to be altered to expose more genes for the processes.
3. this is done by the addition of other molecules.
4.this is a reversible process .

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24
Q

modifications of the histone

A

addition of a methyl group
addition of an acetyl group on the histone

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25
Q

is histone modification reversible

A

yes

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26
Q

what kind of replication is the DNA replication

A

DNA replication is bidirectional and semiconservative

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27
Q

process of DNA replication

A

leading and lagging strand with the leading moving from the 5 end towards the 3 end , the lagging strand is synthesised as okazaki fragments , because it is from the 3 end towards the 5 end

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28
Q

behaviour of chromosomes during cell division

A

they cell chromosomes are most condensed during cell division.
during metaphase they align at the center of the cell .

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29
Q

what is a genome

A

refers to the amount of genes and proteins that are found in an organism .

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30
Q

what are exons and introns

A

exons are the coding region of the newly synthesised pre -mRNA while the introna are the non coding regions that are spliced out of the pre-mRNA during the formation.

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31
Q

why is there 20 amino acids yet there is 64 codons that are possibly to be formed.

A

with the exception of methionine and tryptophan other amino acids are all encoded in more than one codon .

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32
Q

degeneracy of the genetic code

A

with the exception of methionine and tryptophan they are all encoded by more than one codon; that is different codon can all code for the same amino acid

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33
Q

what is the main reason for redundancy

A

prevents the development of mutation.

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34
Q

single point mutations can also cause dysfunctional proteins .

A

a mutated haemoglobin gene causes sickle cell disease , the mutant haemoglobin is a hydrophilic glutamate that is substituted by the hydrophobic valine (Val),( GAA or GAG becomes GUA or GUG )

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35
Q

sickle cell disease manifestation

A

the glutamate amino acid is replaced by valine which is a hydrophobic molecule , this causes clumping up of the haemoglobin chains because they are attracted to each other forming a linear shape.

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36
Q

what is RNA

A

ribo- nucleic acid

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37
Q

types of RNA

A

messenger RNA
transfer RNA
ribosomal RNA

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38
Q

production of RNA

A

mRNA produced during replication and transcription.
Transfer RNA present in the ribosome that
is during translation addition of the amino acids together as they are formed through translation.
ribosomal RNA present in the ribosome subunits in the formation of RNA.

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39
Q

Function of the mRNA

A

Transcribed from DNA.​

Carries information for protein synthesis. ​

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40
Q

start codon

A

Initiation codon also determines the reading frame of the RNA sequence.​

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41
Q

process of transcription

A

transcription of DNA to form MRNA, the MRNA - process known as transcription and takes place in the nucleus.
splicing of the MRNA to remove introns and clump extrons together , happens in the nucleus.
with the help of transfer RNA and Ribosomal RNA proteins are formed.
there is post translational modifications of protein that is produced.
The tRNA sits in the p site and the a site is vacant ,the a site is where the next aminoacyl tRNA binds and there is translation leading to elongation

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42
Q

tRNA function

A

Major role is to translate mRNA sequence into amino acid sequence. ​

Acts as an adapter molecule between the coded amino acid and the mRNA.

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43
Q

production of rRNA

A

in the nucleus , then transported to the cytoplasm where they combine with proteins to form a ribosome.

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44
Q

what is the structure of a chromosome

A

2 chromatids that are joined together
they are joined at the middle by a centromere ,
the heterochromatin is the condensed regions of the chromatin that are inaccessible while the euchromatin is the region that is accessible , not very condensed.
there is a telomere that is located at the end of the end of the chromatin.
the heterochromatin is the most inward compared to the euchromatin .

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45
Q

what is known as telomere

A

telomere are at the edge of the chromosome , they have hundreds of copies , telomere shortening causes the cell to undergo stress which leads to trigerring of apoptosis

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46
Q

telomerase

A

enzyme that causes the addition of telomeres to prevent the shortening .

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47
Q

what are the phases of the cell cycle

A

the g0 phase, the g1 phase , s phase and the g2 phase and lastly the m phase

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48
Q

g1 phase

A

the longest phase of the cell cycle, is 10 to 12 hours long.
there is enlargement of the cell,
presence of a checkpoint ,

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49
Q

s phase

A

replication of the DNA lasts 6 to 8 hours

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50
Q

g 2 phase

A

the cell is preparing to divide

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51
Q

mitosis

A

there is production of 2 identical cells

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52
Q

phases of mitosis

A

IPMAT

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53
Q

prophase

A

the chromosomes have condensed and are visible , the nuclear membrane has disappeared, spindle fibres begin to form

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54
Q

metaphase

A

the chromosomes are at the middle of the cell, the spindle fibres have attached to the centriole , there is maximum condensation of the chromosome

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55
Q

anaphase

A

sister chromatids are separated at the chromosomes longitudinally , they move to the ends of the cell.

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56
Q

telophase

A

the nuclear membrane is formed, each cell will contain 46 chromosomes that is a diploid number.

57
Q

centromere

A

site for the kinetochore microtubules of the spindle fibres ,
it is required for chromosome separation

58
Q

chromatin

A

made up of heterochromatin and euchromatin , and proteins euchromatin is made up of active genes while heterochromatin is made up of silenced genes,

59
Q

what are extragenic sequences

A

sequences that are outside of the coding regions of the gene.

60
Q

examples of tandemly repeated sequences

A

Satellite DNA (14-500 bp repeats in of 20-100 kb arrays, ​
at centromeres and telomeres)( if you do not need it its is spliced out )​

Minisatellite DNA (15-100 bp repeats in 1-5 kb arrays; used for DNA fingerprinting)​

61
Q

example of highly repeated interspersed DNA sequences

A

SINEs (short interspersed nuclear elements, 100-400 bp, most common are Alu elements) ​

LINEs (long interspersed nuclear elements, up to ​
6 kb, most common are L1 elements) ​

62
Q

what is the structure of a chromatin

A

made up of histone proteins and DNA wrapped around it , histones have a positive charge and are packaged into units called nucleosomes.
manny nucleosomes are wrapped around to form a solenoid about 6 nucleosomes are wrapped together .

63
Q

what is the purpose of packaging the DNA into solenoids

A

1.the packaging allows the neutralising of the negatively charged DNA with the positively charged histones .
2.The DNA is able to take less space.
3.Based on the environmental pressure and other reasons the inactive DNA can be folded in accessible regions until when they are required.

64
Q

modification of the histone proteins

A

1.acetylation- that is addition of an acetyl group that will make the histone less positive and cause repulsion exposing the DNA .
2.methylation - addition of a methyl group the histone is the histone is made more positive and there is more attraction between the DNA and the histone protein.

65
Q

metacentric chromosomes

A

Metacentric chromosomes have the centromere near the center of the chromosome

66
Q

acrocentric chromosome

A

Acrocentric means that the centromere is distant from the center.

67
Q

submetacentric

A

Submetacentric means that the centromere is slightly off-center

68
Q

what is a karyotype

A

A karyotype is an individual’s complete set of chromosomes. The term also refers to a laboratory-produced image of a person’s chromosomes isolated from an individual cell and arranged in numerical order.

69
Q

what are is fluorescence in situ hybridization

A

fluorescence in situ hybridization (abbreviated FISH) is a laboratory technique used to detect and locate a specific DNA sequence on a chromosome.

70
Q

what are the types of FISH probes

A

1.unique sequence probes
2.centromeric probes for determining the chromosome number.
3.telomeric probes that is useful for detecting subtelomeric rearrangements and is often present in children with mental retardation.
4.whole chromosome probes which measures a cocktail of probes covering different parts of a particular chromosome .

71
Q

process of meiosis

A

cell division in germ line cells to form haploid cells .The chromosomes are passed on as re-arranged copies which creates genetic diversity.

72
Q

prophase 1

A

there is recombination between the non -sister chromatids ,there is crossing over where the allele bind and exchange materials.

73
Q

metaphase 1

A

independent assortment of the chromosomes in the middle of the cell

74
Q

gametogenesis

A

the process of formation of an egg or a sperm

75
Q

oogenesis

A

Oogenesis = process of egg formation

76
Q

spermatogenesis

A

process of sperm formation​

77
Q

difference between oogenesis and spermatogenesis

A

in oogenesis after meiosis 2 there is only one viable cell that proceeds into differentiation and becomes an egg the rest become polar bodies .however, in spermatogenesis, in meiosis 2 the 4 cells that are possibly released all go into differentiation to form sperms hence the maturation once in a month.

78
Q

what are the differences between gametogenesis in males and women.

A

on a table

79
Q

fertilisation

A

Two haploid cells (egg, sperm) form 1 diploid cell (zygote) – develops into embryo​

Whether sperm contain an X or Y chromosome determines if embryo is female (XX) or male (XY)​

Embryo contains an assortment of genes from each original parent – more genetic diversity​

Mitochondria (and their DNA) come only from mother via the egg – maternal inheritance

80
Q

what is a centromere

A

constricted region that joins the sister chromatids
made up of repetitive DNA sequences
site for the kinetochore attachment

81
Q

extragenic sequences

A

1.tandemly repeated DNA sequences -Satellite DNA has repetition of 14 to 500 base pairs ( centromeres and telomeres ) while minisatellite has repetition of 15 to 100 base pairs ( fingerprint).
2.highly repeated interspersed DNA sequences.( that is long interspersed nuclear elements and short interspersed nuclear elements)

82
Q

nucleosome packaging units

A

146 base pairs wrapped in 1.8 turns around 8 histone proteins.

83
Q

levels of the condensed chromatin structure

A

level one - nucleosome
level 2 - chromatin fibre
level 3 - fibre scaffold complex
level 4- chromosome

84
Q

condensation factor of DNA at the metaphase

A

factor of *10000 during metaphase for the DNA to be seen really well

85
Q

what scientific steps does the FISH method involve

A

labelling with the fluorescence dye , denaturing of the DNA and later hybridization.

86
Q

structure of a chromosome

A

made up of 2 chromatids.
p arm , the top arm while the q arm is the bottom arm of the chromatid.

87
Q

metacentric chromosome

A

the arms seem almost at the same length
the centromere is located at the middle

88
Q

sub metacentric chromosomes

A

the centromere is placed slightly away from the centre and the p arms are shorter but existing

89
Q

acrocentric

A

the centromere is located almost at the apex very short to non existent p arm .

90
Q

telocentric

A

the centromere is at the telomere hence the name telocentric there is no p arm.

91
Q

what is the most prevalent Stage with incidence of chromosomal abnormalities

A

first trimester miscarriages that is 50%
children with mental retardation that is 35-40%
congenital malformations that is 5-10%

92
Q

what are the types of chromosomal abnormalities

A

numerical
structural
mutational

93
Q

what is the origin of chromosomal abnormalities

A

non -disjunction

94
Q

syndrome caused by trisomy

A

patau - XX +13
down syndrome -XY+21
edwards -XX+18

95
Q

describe non -disjunction

A

could happen at the meiosis one whereby two chromosomes are located on the same cell.
could happen in meiosis 2 whereby
there is failure of separation of the
sister chromatids such that each
cell has a sister chromatid instead
of a chromosome ; because of this one cell may end up with more chromosomes while another might end up with nothing on the cell.

96
Q

origin of disomy

A

male partners

97
Q

origin of trisomy

A

female partners

98
Q

trisomy 21

A

inheritance of extra chromosome at location 21 which causes down syndrome.
trisomy 21 caused by non -disjunction , robertsonian translocation 4% and mosaicism (1%)

99
Q

what are the characteristics of someone with downs syndrome

A

Characteristic facial dysmorphologies​

IQ less than 50​

Average life expectancy (50-60 years)​

Alzheimer’s disease in later life​

100
Q

trisomy 13

A

causes Patau syndrome
extra chromosome at position 13
mostly caused by non -disjunction and mostly of maternal origin ,
also caused by unbalanced robertsonian translocation

101
Q

trisomy 18

A

edwards syndrome
severe development problems and most patients will die within the first year.

102
Q

examples of syndromes that are autosomal chromosomes aneuploidy

A

downs syndrome
edwards syndrome
patau syndrome

103
Q

sex chromosomes aneuploidy syndromes

A

turners syndrome klinefelters syndrome

104
Q

turners syndrome

A

example of monosomy
only one sex chromosome that is X only happens in women ( can only be a man if there is a y chromosome, with this there is only an x)

105
Q

characteristics of turner`s syndrome

A

emales of short stature and infertile- males cannot have this.​

Neck webbing and widely spaced nipples​

Intelligence and lifespan is normal​

106
Q

klinefelter`s syndrome

A

an extra sex chromosome
only in males

107
Q

characteristics of klinefelter`s syndrome

A

tall stature in men and long limbs
sterility ( infertile )
mild learning disabilities
small testes
males with gynacomastia

108
Q

structural abnormalities of chromosomes

A

1.Balanced or unbalanced rearrangements​

2.Translocations​

Reciprocal: involving breaks in two chromosomes with formation of two new derivative chromosomes​

Robertsonian: fusion of two acrocentric chromosomes​

3.Deletions​

4.Insertions​

5.Inversion

109
Q

what are structural abnormalities

A

abnormalities that cause changes in the chromosome structure .

110
Q

what is a balanced translocation

A

.there is no gain or loss of the genetic material , the genetic material is only rearranged with materials from both chromatids on both sides ..

111
Q

outcomes for someone who is a balanced translocation carrier

A

there is a cell that is a fertilised carrier

112
Q

unbalanced translocation

A

robertsonian translocation
reciprocal translocation

113
Q

robertsonian translocation

A

fusion of acrocentric chromosomes at their centric ends and there is loss of the 2 p short arms. the q arms fuse to form a chromosome.

114
Q

outcomes for robertsonian translocation

A

two unbalanced gametes fertilisation with a normal balanced gamete will form both trisomy , monosomy at chromosome 21 and 14.

115
Q

deletion

A

breaks of some parts of the chromosome

116
Q

inversion

A

also known as balanced rearrangement
there is an inversion of the genetic material which is reinstated in the piece of DNA.

117
Q

what are genetic mutations

A

changes in the structure of the DNA could be in the germline or could be somatic

118
Q

genetic mutation s

A

Germline or somatic​

Gene disruption /disease-associated​

Polymorphism​

No phenotypic effect​

Frequency >1%​

119
Q

where does genetic mutation happen in the gene

A

genetic mutations could be in the coding region or in the non coding region

120
Q

examples of genetic mutations

A

silent
missense
non -sense
frame shift

121
Q

silent mutation

A

synonymous e.g. CGA (Arg) to CGC (Arg), they both have the same outcome because they result in the same amino-acid formation

122
Q

non -sense mutation

A

Nonsense e.g. CGA (Arg) to TGA (Stop) Intro of a stop codon earlier on ​

123
Q

frameshift deletion and insertion

A

GA (Arg) to ​CCGA (Pro, then out-of-frame)​

124
Q

missense mutation

A

instead of formation of a specific amino acid there is formation of another ; example Missense e.g. CGA (Arg) to GGA (Gly)

125
Q

methods of detecting mutations

A

1.polymerase chain reaction
2.gel electrophoresis
3.restriction fragment length polymorphism analysis.(RFLP)
4.amplification refractory mutations system (ARMS )
5.DNA sequencing

126
Q

necessities for PCR

A

Sequence information​

Oligonucleotide primers​

DNA​

Nucleotides​

DNA polymerase​

Making more of the dna and the separate nucleotides labelled with flouroscent.

127
Q

techniques for PCR

A

denaturation - that is breaking of the hydrogen bonds across the 2 strands.
annealing that is cooling the reaction so that the primers can bind to their complementary sequences on the single stranded DNA template.
extending with the primer addition for formation of new base pairs.

128
Q

polymerase chain reaction

A

amplification of the DNA molecules which will result in the formation of many DNA molecules.
uses the DNA polymerase hence the name for extension of the DNA.

129
Q

gel electrophoresis in PCR

A

technique in which fragments of DNA are pulled through a gel matrix by an electric current , and it separates DNA fragments according to its size.

130
Q

gel electrophoresis

A

Separate DNA fragments by size​

Apply an electric field​

DNA is negatively charged​

Separate through agarose gel matrix​

Visualise DNA fragments​

131
Q

interpretation of a gel electrophoresis photo

A

the small molecules will move towards the bottom of the paper ,

132
Q

advantages of PCR gel photo

A

Speed​

Ease of use​

Sensitive​

Robust

133
Q

PCR applications

A

DNA cloning​

DNA sequencing​

In vitro mutagenesis​

Gene identification​

Gene expression studies​

Forensic medicine​

Typing genetic markers​

Detection of mutations​

134
Q

what are the outcomes for translocation

A

normal with normal gamete
carrier with balanced chromosomes
unbalanced chromosome which might lead to partial trisomy and monosomy

135
Q

mutation nomenclature

A

1.Cys64Arg - cysteine is replaced by arginine
2.662-42C >T- that is at position 42 of the 662 extron cytosine is replaced( substituted) with thymine.
3.

136
Q

applications of PCR

A

DNA cloning​

DNA sequencing​

In vitro mutagenesis​

Gene identification​

Gene expression studies​

Forensic medicine​

Typing genetic markers​

Detection of mutations

137
Q

arms method disadvantages

A

Need sequence information​

Limited amplification siz

138
Q

arms method advantages

A

Cheap​

Labelling not required​

Electrophoresis required​

Primer design critical​

139
Q
A

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