topic 3 - genetics Flashcards
(146 cards)
1
Q
what is DNA
A
genetic blueprint which codes for and determines the characteristics of an organism
2
Q
what is a gene
A
sequence of DNA that encodes for a specific trait
3
Q
what is a locus
A
position of a gene on a particular chromosome
4
Q
what is an allele
A
alternate form of a gene that codes for the different variations of a specific trait
5
Q
what is an example of a gene and its potential allelic variations?
A
eye colour
brown, blue, green, grey
6
Q
what is a gene mutation
A
change in the nucleotide sequence of a section of DNA coding for a specific trait
7
Q
what is formed as a product of mutation?
A
new alleles
8
Q
what are the three types of gene mutations
A
beneficial (missense mutations, new variations of a trait)
detrimental (nonsense mutations, abrogate the normal function)
neutral (silent mutations, have no effect on the functioning)
9
Q
what is an example of a disorder caused by a gene mutation?
A
sickle cell anemia
10
Q
what is sickle cell anemia caused by
A
base substitution (single base is changed in the gene sequence)
6th codon position for the beta chain of hemoglobin is changed
11
Q
sickle cell anemia changes to DNA, mRNA, and polypeptide chain?
A
DNA: GAG –> GTG
mRNA: GAG –> GUG
Polypeptide: glutamic acid –> valine
12
Q
what are the consequences of sickle cell anemia?
A
- alters hemoglobin structure (forms insoluble strands)
- cannot transport oxygen effectively (causes fatigue)
- red blood cells adopt a sickle shape (may form clots)
- sickle cells are destroyed at a higher rate (causes anemia)
13
Q
what is the genome
A
totality of genetic information of a cell, organism or organelle (includes all genes)
14
Q
what does the human genome consist of
A
46 chromosomes
3 billion base pairs
21,000 genes
15
Q
what is the Human Genome Project (HGP)?
A
international cooperative venture established to sequence the human genome (showed that humans share the majority of their sequence)
16
Q
where is the genetic material found in prokaryotes?
A
cytoplasm, in the nucleod
17
Q
differences between prokaryotic and eukaryotic DNA?
A
prokaryotic DNA:
- single circular molecule made of naked DNA
- may have additional plasmids
eukaryotic DNA:
- multiple linear NA molecules packaged with histones
- no plasmids (unless genetically modified)
18
Q
what are plasmids
A
circular DNA molecules
19
Q
what do homologous chromosomes share
A
- the same structural features (ex. same size, same branding pattern)
- the same genes at the same loci positions
20
Q
what are homologous chromosomes
A
paired chromosomes inherited from both parents (maternal + paternal) in sexually reproducing animals
21
Q
diploid vs haploid?
A
diploid: 2 sets of chromosomes (i.e. body cells, as they receive genetic material from both parents)
haploid: 1 set of chromosomes (organisms only pass on half of their genetic material to reproduce)
22
Q
what happens when haploid sex cells fuse?
A
diploid cell, grows into an organism
23
Q
how is sex determined in humans?
A
sex chromosomes
24
Q
what sex chromosomes do females possess? males?
A
females: XX
males: XY
25
what is the Y chromosome responsible for?
development of the male sex characteristics
26
what happens when there is no Y chromosome?
female sex organs develop
27
why is the father responsible for determining the sex of the offspring?
if the sperm contains a Y chromosome, embryo = boy
X chromosome = girl
the female egg will always have an X chromosome
28
what are the remaining chromosomes in the organism (not sex chromosomes)
autosomes
29
how many homologous autosomes do humans have
22 pairs
30
what are karyotypes?
number and types of chromosomes in a eukaryotic cell
31
what is a karyogram
shows the chromosomes of a cell in homologous pairs of decreasing length
32
when and why is karyotyping usually used?
occurs prenatally to...
- determine the gender of the unborn child
- test for chromosomal abnormalities
33
what is Down Syndrome?
condition whereby the individual has three copies of chromosome 21 (i.e. trisomy 21)
34
how does autoradiography work
- radioactive thymidine is incorporated into a cell's DNA
- chromosomes were fixed to a photographic surface and treated with AgBr
- radiation converts silver ions into insoluble grains that is visible via electron microscopy when a film is developed
35
what is the point of autoradiography?
to measure the length of DNA molecules while uncoiled
36
who pioneered autoradiography?
John Cairn
37
can organisms with different diploid numbers interbreed?
unlikely as they cannot form homologous pairs in zygotes
when they do breed, offspring are infertile
38
what is chromosome number a characteristic feature of (?)
members of a particular species
ex. horses (diploid = 64)
39
summary of meiosis I?
- reduction division
- separates homologous chromosomes
- crossing over may occur during Prophase I
40
summary of meiosis II?
- akin to mitotic division
- separates sister chromatids
- occurs b/c DNA is replicated in interphase to create chromosomes with sister chromatids
41
what is meiosis?
reduction division of a diploid cell to produce four haploid cells (gametes) that are genetically distinct
42
what are the two cellular divisions of meiosis?
meiosis I - separates pairs of homologous chromosomes
meiosis II - separates sister chromatids
43
what are sister chromatids?
identical DNA molecules produced in the S phase of interphase held together by a centromere
44
what happens during prophase i?
chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
45
what happens during metaphase i?
spindle fibres connect to bivalents + align them along the middle of the cell
46
what happens during anaphase i?
spindle fibres contract + split bivalent, homologous chromosomes move to opposite poles of the cell
47
what happens during telophase i?
chromosomes decondense, nuclear membrane may reform, cytokinesis
48
what happens during prophase ii?
chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
49
what happens during metaphase ii?
spindle fibres from opposing centrosomes attach to chromosomes at centromere and align them along cell equator
50
what happens during anaphase ii?
spindle fibres contract + separate the sister chromatids, chromatids move to opposite poles
51
what happens during telophase ii?
chromosomes decondense, nuclear membrane reforms, cytokinesis
52
what is the final outcome of meiosis?
four haploid daughter cells
53
what are chiasmata
points where the homologous chromsomes are held together
54
what is synapsis
homologous chromosomes pairing up to form a bivalent
55
what is recombination
new gene combinations formed on chromatid
56
what are recombinants
nonsister chromatids that have exchanged DNA
57
number of possible gamete combinations?
2^n where n = haploid number
58
T/F: the orientation of pairs of homologous chromosomes is not random
F, random
59
what would happen if chromosome number was not halved in gametes?
polyploidy as the total chromosome numbers would double each generation
60
what are the three main sources of genetic variation arising from sexual reproduction?
- crossing over (prophase i)
- random assortment of chromosomes (metaphase i)
- random fusion of gametes from different parents
61
what is non-disjunction
chromosomes failing to separate correctly
62
what does nondisjunction result in
gametes w/ one extra or one missing chromosome
63
what is the effect of the age of parents on the chances of nondisjunction?
strong correlation between maternal age and occurence of non-disjunction events
64
what is DISCO PUG? (mitosis/meiosis differences)
```
Divisions (1 vs 2)
Independent Assortment (N vs Y)
Synapsis (N vs Y)
Crossing over (N vs Y)
Outcome (2 cells vs 4 cells)
Ploidy (dip --> dip, dip --> hap)
Use (body cells vs sex cells)
genetics (identical vs genetic variation)
```
65
what is a genotype
allele combination for a specific trait
66
what is a penotype
physical expression of a specific trait
67
what are phenotypes determined by
genotype + environmental factor
68
what are the three possible types of allele combinations?
homozygous (both alleles are the same)
heterozygous (alleles are different)
hemizygous (only one allele, ex. X/Y gene in males)
69
what did Gregor Mendel's pea experiment establish
principles of inheritance
70
what were the findings of Mendel's pea experiment?
organisms have heritable factors
parents contribute equally to inheritance by supplying one version of the gene each
gametes contain only one allele of each gene
fusion of gametes results in zygotes with two alleles of each gene
71
what are gametes
haploid sex cells formed by meiosis
72
what are the two main modes of inheritance?
complete dominance
| co-dominance
73
what is complete dominance? how is it expressed?
one allele is expressed over another
dominant is expressed in heterozygote (capitale)
recessive is masked in heterozygote (lower case)
74
can recessive phenotypes be expressed in heterozygotes?
no, only homozygotes as heterozygotes display the dominant phenotype
75
what is codominance
both alleles are equally expressed in the phenotype
76
what is an example of codominance?
ABO blood system
77
how is codominance expressed?
superscripts for the different co-dominant alleles (recessive still lower case)
78
how are human red blood cells categorized into different blood groups?
structure of a surface glycoprotein (antigen)
79
A,B, and O alleles are all controlled by a single gene. Which allele is recessive and which two are co-dominant?
A + B alleles = codominant
| O = recessive
80
what does a monohybrid cross determine
allele combinations for potential offspring for one gene only
81
monohybrid cross steps?
designate letters to represent alleles
identify genotype / phenotype of parents
determine genotype of gametes
work out gamete combination with punnett grid
identify ratios of offspring
82
why were Mendel's results questioned
too close to the exact ratios predicted to be genuine
83
what causes genetic diseases
mutations to a gene / genes
84
what type of allele (recessive, dominant, codominant) is responsible for the most common type of genetic diseases (????0
recessive
85
what is autosomal dominance?
both parents are affected by a trait but any offspring is not - trait is DOMINANT (parents are heterozygous)
86
what is autosomal recessive?
neither parents is affected by the trait but any offspring is, the trait must be RECESSIVE (parents must be heterozygous)
87
who is a carrier
heterozygous individuals that possess one copy of the faulty allele but do not develop disease symptoms
88
how many copies of a faulty allele does an autosomal recessive genetic disease require?
both alleles
89
how many copies of a faulty allele does an autosomal dominant genetic disease require to cause the disorder?
one copy
90
how many copies of a faulty allele does a genetic disease caused by co-dominant alleles require to occur
one copy
91
example of an autosomal recessive genetic disease?
cystic fibrosis
92
example of an autosomal dominant genetic disease?
huntington's disease
93
example of a genetic disease caused by co-dominant alleles?
sickle cell anemia
94
what is cystic fibrosis + what is it caused by?
- caused by mutated CFTR gene (chromosome 7)
| - produces thick mucus that clogs airways and causes respiratory issues
95
what is huntington's disease + what is it caused by?
- caused by mutated HTT gene (chromosome 4)
| - amplification of CAG repeats leading to neurodegeneration
96
what is sickle cell anemia + what is it caused by?
- mutated HBB gene (chromosome 11)
| - leads to anemia + other complications
97
why are many genetic diseases rare?
any allele that adversely affects survival is unlikely to be passed on to offspring as the capacity to reproduce is unlikely
98
what is sex-linkage
gene controlling a characteristic is located on a sex chromosome
99
why are sex-linked conditions usually X-linked?
Y chromosome is much much shorter than the X chromosome and contains less genes
100
why can only females be carriers?
heterozygote for the recessive disease condition, males cannot be heterozygous carriers
recessive trait can be masked
101
what are two examples of X-linked recessive conditions?
red-green colour blindness
| haemophilia
102
T/F: for recessive X linked conditions, affected mothers must have affected sons
T
103
T/F: for dominant X linked conditions, affected fathers MUST have affected daughters
T
104
what is a gene mutation
change to the base sequence of a gene that can affect the structure and function of the protein it encodes
105
what are spontaneous mutations
mutations caused by copying errors during DNA replication
106
what are induced mutations
mutations caused by exposure to external elements
107
what are three factors which can induce mutations?
radiation
chemical
biological agents
108
what are mutagens
agents which increase the rate of genetic mutations
109
what are carcinogens
mutagens which lead to the formation of cancer
110
what are two major examples of radiation exposure
nuclear bombing of hiroshima
| accident/meltdown in chernobyl
111
what are some of the long-term consequences of radiation exposure?
- increased incidence of cancer
- reduced immunity (T cell count down)
- congential abnormalities
- organ specific health effects
112
what is a pedigree?
chart of the genetic history of a family over several generations
113
what are the symbols of a pedigree?
```
males = squares
females = circles
affected individual = shaded
unaffected individual = unshaded
mating = horizontal line
generations = roman numerals
age = left to right
```
114
can sex linkage be confirmed with a pedigree?
NO but patterns are there!
115
what is the polymerase chain reaction? (PCR)
artificial method of replicating DNA under laboratory conditions
116
what is gel electrophoresis?
laboratory technique used to separate and isolate proteins or DNA fragments based on mass/size
117
how does gel electrophoresis work?
samples placed in a block of gel + current is applied
smaller samples move faster through the gel (lower resistance)
samples move towards the anode
DNA is negatively charged (b/c of phosphate group)
proteins are treated with an anioinic detergent to impart a uniform negative charge on all molecules
118
what is DNA profiling?
technique by which individuals can be identified and compared via their respective DNA profiles
119
when is DNA profiling most commonly used?
```
forensic investigations
paternity tests (offspring STRs are a combination of parents)
```
120
what are STRs? (short tandem repeats)
different lengths of particular DNA segments
121
how does DNA profiling work?
STR's are amplified by PCR then separated by gel electrophoresis for comparison
unique profiles appear when multiple loci are compared
122
what is a transgenic?
new organism created as a result of gene modification
123
why an an organism potentially express a new trait if the appropriate gene is introduced into its genome?
genetic code is (almost) universal
124
process of gene transfer?
1. DNA extraction (amplified using PCR)
2. digestion + ligation (specific restriction enzyme + DNA ligase)
3. transformation and expression (plasmid inserted into host cell + antibitioc to select for successful transgetic cells)
125
benefits of GM crops?
- can grow in a wide range of environments
- reduce farming costs + deforestation
- reduces spoilage
- improve nutritional standards
126
risks of GM crops
- unexpected health issues
- restrict access due to patent protections
- cross pollination with weeds
- reduce biodiversity (competes w native plants)
127
what is an example of GM crop + risks to wildlife?
Bt corn, incorporates insecticide producing gene which is toxic to monarch muterflies
128
what are clones
groups of genetically identical organisms or a group of cells derived from a single original parent cell
129
what does cloning multicellular organisms require
production of stem cells
130
how can stem cells be artificially generated
somatic cell nuclear transfer (SCNT)
131
how does somatic cell nuclear transfer work?
somatic cells are removed from donor + cultured
enucleated egg cell is fused with nucleus from donor to make a diploid egg
electric current stimulates egg to develop into embryo
embryo is implanted into surrogate
132
what are animal cloning methods?
binary fission
budding
fragmentation
parthenogenesis
133
what are plant cloning methods?
vegetative propogation
134
what are human cloning mechanisms?
natural mechanisms (identical twins)
135
what is binary fission
parental organism divides equally into two clones
ex. flatworms
136
what is budding
cells split off from parent, generating smaller clones
occurs in hydra
137
what is fragmentation
new organisms grow from separated fragment of parent
ex. annelid worm
138
what is parthenogenesis
embryos formed from an unfertilized diploid ova
ex. fish
139
what is vegetative propagation
small pieces of plant acn be induced to grow independently
140
why are plants capable of vegetative propagation?
adult plants possess totipotent meristematic tissue
141
what is a stem cutting
separated portion of a plant stem that is used to regrow a new clone
142
difference between identical and nonidentical twins?
identical twins: fertilized egg splits into 2
nonidentical: nonfertilized egg splits into 2, fertilized by diferent sperm
143
what are the two forms of artificial cloning
embryo cloning
| adult cloning
144
what is embryo cloning + how does it work
cloning from an embryo by separating the embryonic cells into groups
embyronic stem cells are pluripotent so each cell can potentially form a cloned off spring
145
why can we not control the genetic features of potential clones in embryo cloning?
occurs after random fertilization
146
what is adult cloning?
process of somatic cell nuclear transfer
SCNT
