chapter 3 Flashcards
(126 cards)
1
Q
dna
A
genetic blueprint codes for characteristics of organism
2
Q
dna packaged. into discrete structures
A
chromosomes
3
Q
gene
A
sequence of dna coding for specific trait (trait may be influenced by multiple genes)
4
Q
locus (plural: loci)
A
position of gene on particular chromosome
5
Q
allele
A
alternative form of gene coding for different variations of specific traits
6
Q
as alleles are alternative forms of 1 gene
A
gene sequences = similar
alleles differ by 1 or a few bases
7
Q
gene mutation
A
change in nucleotide sequence of section of dna coding for specific trait
new alleles formed by mutation
8
Q
gene mutations can be
A
benefical, neutral, detrimental
9
Q
beneficial gene mutation
A
change gene sequence to create new variations of trait
10
Q
detrimental gene mutation
A
shorten gene sequence and stop normal gene function
11
Q
neutral gene mutation
A
have no effect on functioning of feature
12
Q
sickle cell anemia (eg of disorder caused by gene mutation)
A
single base was changed in gene sequence (base substitution mutation)
change to 6th codon for beta haemoglobin chain
dna: change GAG to GTG on non transcribed strand (CTC to CAC on template strand)
mRNA: changes from GAG to GUG at 6th codon
polypeptide: 6th amino acid on beta chain of haemoglobin changed from glutamic acid to valine
13
Q
consequence of sickle cell anemia
A
alters haemoglobin structure causing formation of insoluble fibrous strands
insoluble haemoglobin cannot carry oxygen as effective (causing tiredness)
haemoglobin changes causes shape of red blood cell to change shape (sickle shape)
sickle cells may form clots in capillaries blocking blood supply to vital organs+ causing myriad health issues
sickle cells destroyed faster than normal cells, so low red blood cell count
14
Q
genome
A
all genetic info of cell, organism or organelle
includes all genes + non coding dna sequences
(intron, promoters, etc)
15
Q
human genome
A
46 chromosomes
~3 million base pairs
~21000 genes
16
Q
human genome project
A
established to sequence human genome
completion (2003) led to many outcomes
17
Q
outcomes of human genome project (hgp)
A
mapping: n.o, location, size human genes
screenings: allowed production of specific gene probes, detecting sufferers/carriers of genetic disease
medicine: discovery of proteins led to improved treatments
ancestry: comparisons with other genomes provide info on origins, evolution + migratory patterns of man
18
Q
n.o of genes
A
differ between species + not indicator of biological complexity
19
Q
n.o genes in genome predicted by
A
identifying sequences common to genes
identifying regions may include expressed sequence tags or sequences homologous to known genes
presence of pseudogenes/transposons make accurate counts of unique gene numbers difficult
20
Q
different approaches to. calculating n.o of genes means
A
final estimations vary significantly
21
Q
prokaryotes
A
no nucleus
genetic material free in cytoplasm in nucleoid region
22
Q
genophore
A
genetic material of a prokaryote consisting of single chromosome consisting of circular dna molecule
23
Q
in addition to genophore, prokaryotic cells can possess additional circular dna molecule
A
plasmids
24
Q
plasmids location
A
present in some prokaryotic cells, not naturally in eukaryotic cells
25
bacterial conjugation
when bacterial cells exchange plasmids via their sex pili
allowing bacteria to evolve new features within generation (horizontal gene transfer)
25
bacterial conjugation
when bacterial cells exchange plasmids via their sex pili
allowing bacteria to evolve new features within generation (horizontal gene transfer)
26
plasmids self replication
plasmids can self replicate and autonomously synthesise proteins- so are ideal vectors for gene manipulation in labs
27
genetic material of eukaryote
consists of muliple linear molecules of dna associated w histone proteins
dna packaged w histone proteins for more compact structure= more efficient storage
28
organisation of eukaryotic chromosomes
dna complexed w 8 histone proteins (octamer) to form nucleosome
nucleosomes linked by additional histone protein (H1 histone) forming string of chromotasomes,
coiling to form solenoid structure,
condensed to form 30nm fibre
fibres form loops that are compressed and folded around protein scaffold to form chromatin
chromatin supercoils during cell division to form chromosomes = visible under microscope when stained
29
eukaryotic chromosomes
linear molecules of dna compacted during cell division (mitosis/meiosis)
30
centromere
constriction point fo each chromosome, dividing it into two sections (arms)
p arm is shorter section
q arm is longer section
31
eukaryotic species (ref chromosomes)
have multiple chromosomes that may differ in both size/position of centromere
32
locus
position of particular gene on chromosome
33
locus region/location can be identified by 3 points
-n.o or letter which denotes chromosome
-letter (p or q: ref arms - short or long) to denote arm of locus
-n.o corresponding to g band location
34
p arm
shorter
35
q arm
longer
36
sexually reproducing organisms (ref: genetic sequences)
inherit genetic sequences from both parents
37
sexually reproducing organisms inheritance
organism possesses two copies of each chromosome(one maternal, one paternal)
maternal and paternal chromosome pairs = homologous chromosomes
37
sexually reproducing organisms inheritance
organism possesses two copies of each chromosome(one maternal, one paternal)
maternal and paternal chromosome pairs = homologous chromosomes
38
homologous chromosomes share
same structural features (size, bonding patterns, centromere positions)
same genes at same loci positions (genes same, allele may be different)
39
homologous chromosomes must be separated in gametes (meiosis) before reproduction to prevent
chromosome numbers continually doubling w each gen
40
diploid cells
two sets of chromosomes from sexually reproducing organisms inherited from both parents (one set each)
41
gametes
sex cells
42
to reproduce organisms must create gametes with
half the number of chromosomes (haploids)
43
when haploid gametes fuse
resulting diploid cell (zygote) can grow to new organism
44
haploid cells
nuclei w one set of chromosomes (symbolised by n)
these nuclei possess single gene copy (allele) for each trait
all gametes in organism will be ahploid (derived from diploid cells in mitosis)
also present in bacteria (asexual) + fungi (except when reproducing)
45
sex determined by
pair of sex chromosomes (heterosomes)
46
females (ref: sex chromosomes/heterosomes)
possess two copies of X chromosome (XX)
47
males (ref: sex chromosomes/heterosomes)
possess one copy of X and one copy of Y (XY)
48
Y chromosome
containes genes for developing male characteristics (specifically SRY gene)
49
in absense of Y chromosome
female sex organ will develop
50
sex chromosomes = homologous in females (XX) but
are not homologous in males
51
father (ref: sex chromosomes)
will always be responsible for determining sex as they have both X and Y chromosomes
52
if sperm contains X chromosome
girl
53
if sperm contains Y chromosome
boy
54
egg will always (ref: chromosomes)
contain X chromosome
55
remaining chromosomes in organism (that do not determine sex)
autosomes
56
karyotype
n.o + types of chromosomes in eukaryotic cell determined by process involving:
harvesting cells (foetus or white blood cells)
chemically inducing cell division, arresting mitosis when chromosome condensed
stage during which mitosis is halted determines whether chromosomes have sister chromatids or not
57
karyogram
when chromosomes are stained to create a visual profile in which chromosomes organised into homologous pairs according to size
58
karyotyping occurs prenatally and is used to
determine gender of unborn child, test for chromosome abnormalities
59
down syndrome
condition when individual has three copies of chromosome 21
60
autoradiography
cells grown in radioactive thymine-containing solution
tritiated thymine incorporated into chromosomal dna of cell (T not present in RNA)
chromosomes isolated by lysing cells + fixing chromosomes to photographic surface
surface immersed in radioactively sensitive emulsion w silver bromide
radiation released from thymine converts AG+ ions to insoluble metal grains
after exposure period, escess silver bromide = washed away, leaving silver grains to disappear as black dot
whn photographic film= developed, chromosomal DNA visualised w electron microscope
61
chromosome n.o
characteristic feature of members of particular species
62
organsims w different diploid n.o
are unlikely to be able to interbreed (cannot form homologous pairs in zygotes)
if interbreed, infertile offspring (= no functional gamete formation)
horse(diploid: 64) + donkey (diploid 62) = mule (non-diploid 63)
63
chromosome n.o doesnt provide indication of genetic complexity
tomatoes: 24 chromosomes, genome size 950 mill bp and 32000 genes
chicken: 78 chromosomes, genome size 1.2 bill bp and 17000 genes
64
genome size
varies between organism and doesnt indicate genetic complexity
65
general rule
bacteria + viruses have small genomes
prokaryotes ususally have smaller genomes than eukaryotes
size of plant genomoes can vary dramatically bc of capacity for plant species to self fertilise and become polyploid
66
meiosis
process where gametes are made in reproductive organs, involving reduction division of diploid germline cells into 4 genetically distinct haploid nuclei
67
process of meiosis = 2 cellular divisions (w same stage
-1st meiotic divisions separates pairs homologous chromosomes to 1/2 chromosome n.o (diploid to haploid)
-2nd meiotic division separate sister chromatid (created by replication of dna during interphase)
68
meiosis I
=reduction division (diploid → haploid) where homologous chromosomes = separated
69
prophase I
chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
70
metaphase I
spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
71
anaphase I
Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
72
telophase I
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
73
meiosis II
2nd division separates sister chromatids (chromatids may not be identical bc crossing over in prophase I)
74
prophase II
Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
75
metaphase II
Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
76
anaphase II
spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
77
telophase II
Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
78
final outcome of meiosis
4 haploid daughter cells
(may all be genetically distinct if crossing over occurs in prophase I (causes recombination of sister chromatids)
79
synapsis
occurs in prophase I, is when homologous chromosomes pair up to form bivalent
chromosomes are held together at point = chiasmata
80
crossing over of genetic material between non-sister chromatids can occur at
chiasmata
81
crossing over
result of exchange of genetic material, new gene combinations formed on chromatids (recombination)
if crossing over occurs all 4 haploid daughter cells will be genetically distinct (sister chromatids =no longer identical)
82
once chiamata formed
the homologous chromosomes condense as bivalents + then separated in meiosis
83
metaphase I homologous chromosomes line up at equator as bivalents in 1 of 2 arrangement
Maternal copy left / paternal copy right
OR
paternal copy left / maternal copy right
84
orientation of homologous chromosomes =
random, as is subsequent assortment of chromosomes into gametes
final gametes will differ depending on if got the maternal or paternal copy of chromosome following anaphase I
85
as random assortment will occur for each homologous pair, n.o of possible gamete combinations = dependent on
n.o of homologous pairs
86
Gamete combinations
= 2n (where n represents the haploid number)
87
Most sexually reproducing organisms are diploid
they have two copies of every chromosome (maternal / paternal)
88
to reproduce diploid organisms must make gametes that are
haploid (one copy of each chromosome)
89
fertilisation of 2 haploid gametes (egg+sperm) results in
diploid zygote formation, that can grow via mitosis
90
if chromosome n.o was not halved (diploid to haploid
total chromosome n.o would double each gen (polyploidy)
91
advantage of meiotic division + sexual reproduction =
promotes genetic variation in offspring
92
3 main sources of genetic variation arising from sexual reproduction:
crossing over (prophase 1)
random assortment chromosomes (metaphase 1)
random fusion of gametes from different parents
93
crossing over
involves exchange of segments of dna between homologous chromosomes (prophase 1)
(occurs between non sister chromatids in chiasmata
94
consequent of recombination in crossing over
all chromatids comprising bivalent = genetically different
95
recombinants
chromatids consisting of a combination of DNA from both homologous chromosomes
96
offspring w recombinant chromosomes
will have unique gene combinations, not present in either parent
97
random orientation
When homologous chromosomes line up (metaphase I), their orientation towards opposing poles = random
98
orientation of each bivalent occurs independently, meaning:
different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I
99
bivalent meaning
the association of 2 replicated homologous chromosomes having exchanged DNA strand in at least 1 site called chiasmata. Each bivalent contains minimum of 1 chiasma + rarely more than 3.
100
The total number of combinations that can occur in gametes
2n - where n = haploid n.o of chromosomes
101
Humans have 46 chromosomes (n = 23)
so can produce 8,388,608 different gametes (2^23) by random orientation
If crossing over occurs, the n.o of different gamete combinations becomes immeasurable
102
random fertilisation
fusion of 2 haploid gametes results in formation of diploid zygote
zygote can divide by mitosis + differentiate to form developing embryo
103
As meiosis results in genetically distinct gametes, random fertilisation by egg + sperm will always generate
different zygotes
104
Identical twins are formed________
after fertilisation,
by the complete fission of zygote into two separate cell masses
105
non-disjunction
chromosomes failing to separate correctly resulting in gamete w 1 extra or1 missing chromosome (aneuploidy)
106
failure of chromosomes to separate may occur via:
Failure of homologues to separate in Anaphase I (result = four affected daughter cells)
Failure of sister chromatids separation in Anaphase II (resulting = 2 daughter cells being affected)
107
Chromosomal Abnormalities
If zygote is formed from gamete that has experienced non-disjunction event, resulting offspring will have extra/missing chromosomes in every cell of body
108
Conditions that arise from non-disjunction events include:
Patau’s Syndrome (trisomy 13)
Edwards Syndrome (trisomy 18)
Down Syndrome (trisomy 21)
Klinefelter Syndrome (XXY)
Turner’s Syndrome (monosomy X)
109
Down Syndrome
Individuals w Down syndrome have three copies of chromosome 21 (trisomy 21)
1 of the parental gametes had 2 copies of chromosome 21 as result of non-disjunction
other parental gamete was normal + had single copy of chromosome 21
When 2 gametes fused in fertilisation, resulting zygote had three copies of chromosome 21
110
Studies show chances of non-disjunction increase as age of parents increase
strong correlation w maternal age + occurrence of non-disjunction events
may be due to developing oocytes being arrested in prophase I until ovulation as part process of oogenesis
111
Other studies also suggest that: (ref non-disjunction)
risk of chromosomal abnormalities in offspring increase significantly after a maternal age of 30
higher incidence of chromosomal errors in offspring as result of non-disjunction in meiosis I
Mean maternal age is increasing, leading to increase in n.o of Down syndrome offspring
112
karyotyping
process where chromosomes = organised + visualised for inspection
113
karyotypic uses
to determine gender of unborn child + test for chromosomal abnormalities
113
karyotypic uses
to determine gender of unborn child + test for chromosomal abnormalities
114
karyotyping process
Cells harvested from foetus before being chemically induced to undertake cell division (so chromosomes are visible)
stage during which mitosis is arrested will determine if chromosomes appear w sister chromatids
last, chromosomes are stained + photographed, the norganised according to structure
The visual profile generated = karyogram
115
Chorionic Villi Sampling
involves removing sample of chorionic villus (placental tissue) via tube inserted through cervix
can be done at ~11 weeks of pregnancy with a slight risk of inducing miscarriage (~1%)
116
Amniocentesis
Amniocentesis involves extraction of small amount of amniotic fluid (contains fetal cells) w needle
usually conducted later than CVS (~16 weeks of pregnancy) w slightly lower risk of miscarriage (~0.5%)
117
pcr (polymerase chain reaction)
artificial method of replicating dna in lab conditions
118
pcr tecqnique used to
amplify large quantities of specific dna sequence from initial minute sample
each reaction cycle doubles amount of dna - standard pcr sequence creates over 1 bill copies (2^30)
119
stages of pcr
PCR occurs in thermal cycler + uses variations in temp to control replication process in 3 steps:
Denaturation – DNA sample = heated to separate into 2 single strands (~95ºC for 1 min)
Annealing – DNA primers attach to 3’ ends of target sequence (~55ºC for 1 min)
Elongation – heat-tolerant DNA polymerase (Taq) binds to primer + copies the strand (~72ºC for 2 min)
120
gel electrophoresis
lab technique used to separate + isolate proteins or DNA fragments based on mass/size
121
gel electrophoresis
samples placed in block of gel + electric current = applied - causes samples to move through gel
smaller samples = less impeded by gel matrix, hence will move faster through gel
samples of different sizes separate due to different speeds
dna + proteins electrophoresis = same basic process, but different protocols
122
Dna separation
dna cut into fragments using endonuclease - different dna samples generate different fragment length
fragments separate bc dna = neg charged due to presence of phosphate group on each nucleotide
dna samples = placed into agarose gel + fragment size calculated by comparing against known industry standards
specific sequences can be identified by incorporating complementary radiolabelled hybridisation probe, transferring separated sequences to membrane + then visualising via autoradiography (southern blotting)
123
protein separation
