Genetics

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Plasmids
small, extra loops of DNA in some prokaryotes
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Properties of eukaryotic chromosomes (4)
1) contains linear DNA molecule 2) associated with histone proteins 3) no plasmids 4) two or more chromosomes
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Properties of prokaryotic chromosomes (4)
1) circular DNA molecule 2) naked (no associated proteins) 3)plasmid often present 4) one chromosome
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Autoradiography
Used since 1940's-technique to find radioactive substances in cells
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Steps of autoradiography
Sections of cell coated in photographic film (left in dark for days/weeks) When view w/ microscope, structure of cell & black dots visible on photographic film. Black dot: radioactive atom
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John Carins
adapted autoradiography by looking at chromosomes of E.Coli. Discovered DNA molecules were cirular &1,100μm long
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Describe how John Carins adapted autoradiography
.Grew e.Coli in radioactive medium tymine (so DNA was labelled but not RNA). Placed on membrane &digested cell walls-DNA spilt.Coate mem. in photographic film& left in dark for 2 months>Lines of black dots showed DNA
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The size of a genome
the total amount of DNA in one set of chromosomes in a species
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Genome size of T2 phage (millions of bp)
0.18
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Genome size of Escherichia coli (millions of bp)
5
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Genome size of D.melanogaster (millions of bp)
140
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Genome size of Homo sapiens (millions of bp)
3,000
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Genome size of Paris japonica (millions of bp)
150, 000
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homologous chromosomes
chromosomes which have the same genes in the same place but may not have the same alleles in those genes
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Number of chromosomes in Homo sapiens (humans
46
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Number of chromosomes in Pan troglodytes (chimpanzee)
48
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Number of chromosomes in Canis familiaris (dog)
78
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Number of chromosomes in Oryza sativa (rice)
24
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Number of chromosomes in Parascaris equorum (horse threadworm)
4
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Diploid nuclei
nuclei contains pairs of homologous chromosomes (46 chromosomes-2n)
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Haploid nuclei
nuclei with only one chromosome of each type (23 chromosomes- n)
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Examples of human haploid cells
Sperm and egg cell gametes
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What happens to two haploid gametes during fertilisation?
gametes fuse together to produce one diploid cell (zygote)
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Two types of sex chromosome
Larger X & smaller Y (23rd pair)
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Karyotype
number & type of chromosomes present in cell or organism
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Karyogram
photograph/diagram showing an organisms chromosomes in homolous pairs of decreasing lengths
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Common uses for karyograms of humans
.Deducing sex of individual, .Diagnosing conditions due to chromosome abnormalities (i.e down syndrome or Klinefelter syndrome)
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Fertilisation
male & female gamete fuse to produce zygote
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How many chromosomes do zygotes have?
Twice as many as as the gametes (46)
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Meosis
process that halves chromosome nom & allows sexual life cycle w/ gamete fusion
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What happens to DNA before/during meiosis?
DNA of chromosomes replicated BEFORE division (each chromosome:2 sister chromatids) BUT DNA is not replicated between 1rst &2nd division of meiosis
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Prophase 1 (4)
Chromosomes pair up, spindle microtubles grow from each pole to the equator, nuclear membrane dissolves, crossing over occurs
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Metaphase 1 (2)
Pairs of chromosomes line across equator, Spindle microtubles attach to different chromosomes to ensure one is pulled one way & other pulled other way
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Anaphase 1 (2)
Each chromosomes still consist of 2 chromatids, Homologous chromosomes pulled to opposite poles: halves chromosome nom
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Prophase 2 (2)
immediately divide again, chromosomes pair up, new spindle microtubes grow from the equator, chromos
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Anaphase 2
centromeres divided making chromatids into separate chromosomes which move to opposite poles
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Telophase 2 (3)
Nuclear membranes reforms, cell membrane pulls inwards to divide. Each nucleus has half as many chromosomes as the parent cell nucleus, Both cells divided into 4 haploid cells
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What are the two processes in meiosis which promote genetic variation?
1)Random orientation of pairs of homologous chromosomes in metaphase 1, Crossing over during prophase 1
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Nom of possible combinations of chromosomes produced by random orientation
2^n in humans, n:23> over 8 million combinations per parent
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crossing over
early stage of meiosis- homologous chromosomes pair up & parts of non-sister chromatids can be exchanged between them>produces chromatids w/ new allele combination
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Non-disjunction
When chromosomes which are meant to separate & move to opposite poles in meiosis dont & move to the same pole>gametes produced with either one chromosomes too many or too few
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Trisomy
a zygote produced with 3 chromosomes of one type instead of 2
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What causes Down syndrome/ trisomy 21
when a child is born w/ three chromosomes of type 21 rather than two (non-disjunction during formation of sperm/egg)
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What increases the chance of downs syndrome?
the age of parents
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Methods for obtaining cells of unborn child for chromosome testing (2)
Amniocentesis & Chlorionic villus sampling (CVS)
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Amniocentesis
Hypodermic needle inserted into abdomen & uterus wall. Sample of amniotic fluid removed>contains cells from the fetus
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Chorionic villus sampling (CVS)
Hypodermic needle inserted into abdomen & uterus wall. cels from chorionic villus (fetal tissues in placenta) removed. CVS higher change of miscarriage (2%) than amniocentesis (1%) (due to risk of maternal or fetal infections)
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George Mendel
'father of genetics'-crossed varieties of pea plants that had different characteristics & deduced the principles on which inheritance was based
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How many seeds did Mendel encounter in the F2 generation?
7,324: 5,474 round & 1,850 wrinkled- from noms created basic ration 3:1
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How did Medel discover the 3:1 ratio? (4)
crossed 2 varieties of pea together>F1 generation had the same characteristics as one of the parents. He allowed F1 to self fertilize> F2 generation contained both original parent types in 3:1 ratio
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What is Mendels pea's show us?
that each pea plant has two alleles of the gene that affects the character. Parents-homologous (have 2 of the same allele- F1:heterozygous- two different alleles. F1 has same characteristics as 1 parent as that parents allele was dominant
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Genotype
the alleles po**e**ed by an organism (i.e **/**)
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Phenotype
the characteristics possessed by an organism (i.e smooth/wrinkled seed)
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P in monohybrid cross
parental generation
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F1
first fillia generation> offspring of P generation
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Segregation
occurs in meiosis. 2 alleles of gene on homologous chromosome move to opposite poles
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What is the cause of large proportions of genetic diseases
recessive alleles of autosomal genes (e.g cystic fibrosis)
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What are all chromosomes (apart from sex chromosomes)?
autosomes
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What is the cause of a small proportion of genetic diseases
dominant alleles of autosomal genes (e.g Huntington's disease)
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Cystic Fibrosis
caused by a recessive allele of a gene coding for a chloride channel. Commonest genetic disease in parts of western Europe- 1:3,000 babies in US. Likelihood of child having cystic fibrosis from two carriers: 25%
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Huntington's disease
neurodegenerative disease cause by dominant allele of gene coding for huntingtin (protein w/ unknown funct.) Develops in adulthood. Likelihood of parent w/ Huntington's passing it onto children:50%
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Pedigree charts
indicate whether a disease is caused by dominant or recessive allele & allow the genotypes of some individual to be deduced
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Sex-linkage
the association of a characteristic with the sex of the individual- gene controlling the characteristic is located only on a sex chromosome
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How does the size of the genes on the Y and X chromosomes affect sex-linkage?
Few genes on Y chromosome. X chromosome is large & has important genes- This means sex-linkage i almost always due to genes of X chromosome.
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Name the four ABO blood groups
A, B, AB and O
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Co-dominant alleles
pairs of alleles that both affect the phenotype when present together in a heterozygote. Neither are recessive or dominant
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Which blood groups are co-dominant
IA ad IB
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multiple alleles
genes with more than two alleles
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Example of multiple alleles
The gene for ABO blood groups- has three alleles; IA, IB and i
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What is the genotype for blood group A?
IA i> i is recessive
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What is the genotype for blood group B?
IB i> i is recessive
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What is the genotype for blood group AB?
IA IB
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What is the genotype for blood group O?
ii
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Punnet grid
grid for predicting the outcome of monohybrid genetic crosses
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Blood group of child with parents of O and AB
there are ii and IAIB geneotypes- could be IAi or IBi, 1:1 Group A to B ratio
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Mutations
random changes to the base sequence of a gene
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base substitution
a mutation that replaces one base in a gene with a different base
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Name two mutagens
. High radiation (x-rays, short/medium UV waves, gamma rays) .Mutagenic chemicals (nitrosamines in tobacco & mustard gas)
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Name the two incidents which can be studied for the effects of radiation
The nuclear accident in Chernobyl & nuclear bombing of Hiroshima
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What is the common feature of Chernobyl &Hiroshima?
radioactive isotopes were released into environment & people were exposed to dangerous radiation levels
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Buclear accident in Chernobyl
Ukraine, 1986> accident caused explosions& fire in the core of a nuclear reactor.
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What was released by the Chernobyl accident (4)
Radioactive iodien-131, caesium-134, caesium-137 & six tonnes of uranium and other radioactive materials
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What were the consequences of the Chernobyl accident? (6)
28 workers died after 3 months & leukemia rates increased .Radioactive Iodine concentrations rose- drinking water & milk undrinkable. Iodine absorbed by thyroid-6,000 cases of thyroid cancer. High radioactive caesium levels in fish in Scandinavia,
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Nuclear bombing of Hiroshima
1945- atomic bomb detonated & killed 90,00-166,000 (either directly or over the following months). Only few buildings remaining
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After the nuclear bombing of Hiroshima, what long-term effect of radiation was found
.Death from cancer (leukemia &others)
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Genetics
study of variation and inheritance
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What is the basic unit for iheritance
the gene
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What is the current estimated nom of genes in a homo sapien (humans)
23, 000
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What is the current estimated nom of genes in a E.coli (gut bacteria)
3,200
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What is the current estimated nom of genes in a Drosophila melanogaster (fruit fly)
14,000
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What is the current estimated nom of genes in a Takifugu gambiae (puffer fish)
25,500
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What is the current estimated nom of genes in a Oryza sativa (rice)
41,000
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What do the estimated nom of genes illustrate? (3)
.Bacteria have less genes than eukaryotes, .Some animals have less genes than humans but some have more, .plants may seem less complex but some have more genes than humans
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Alleles
different forms of the same gene
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Sickle cell anemia
genetic disease in the beta polypeptide gene of hemoglobin (HBB) caused by base subsitiution of A to T. consists of 146 amino acids & common in parts of the world affected by malaria
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How does the mutation causing sickle cell anemia occur
Base substitution of HBB from A to T- causes Hb^a to change into new allele Hb^s- Transcrpition- one codon in mRNA is different> one amino acid in polypeptide is altered (now glutamic acid instead of valine)
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Advantage and disadvantage to sickle cell anemia
Advantage:Can give malaria resistance, Disadvantage: sickle cells may carry less oxygen
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Gene locus
a genes particular position on homologous chromosomes
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How can human gene loci be found?
using the OMIM website (Online Mendelian Inheritance in Man
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What does the number of differences between gene base sequences of two species with a common ancestor indicate
how long ago the two species diverged from the common ancestral species
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What does the GenBank database show?
it compares the base sequence of genes & find out how many differences there are
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What does Polymerase chain reaction (PCR) consist of?
a cycle of stages repeatedly carried out to produce
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What is Gel Eletrophoresis?
a method of separating mixtures of proteins or fragments of DNA, which are charged
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Describe how Gel Eletrophoresis is carried out
Mixture of proteins/DNA fragments placed on thin gel sheet (which acts as a molecular sieve). Electric field applied to the gel bby attaching electrodes to both ends. Depending on if particles are pos or neg, they move towards one of the electrodes>
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The Human Genome Project
Began in 1990- focused on sequencing the entire human genome> meant to take 15 yrs but tech improvements meant it finished in 2000
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Short tandem repeats (STR)
long stretches of DNA made up of repeating bases
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How are STR alleles used in DNA profilling? (3)
.Sample of DNA obtained (must not be contaminated by other DNA), .STR loci copied by PRC (usually from loci 11-13). Separated by gel eletrophoresis> result is pattern of bands. Two pep unlikely to have the same pattern of bands unless identical twins
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When was DNA profiling first used in a forensic investigation & what did it show?
the Enderby double murde case. Showed that the prime suspect was not guilty despite confessing to the murders
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How can DNA profiling be used in Paternity investigations
Children inherit half their chromosomes from each parent> all fragments produced in child should also be produced by either the mum or dad
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Genetic modification
thhe transfer of genes from one species to another
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Genetically modified organisms (GMO)/ transgenic organisms
Organisms that have had genes transferred into them
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What is a vector in gene transfer?
small loop of DNA (plasmid) which are used to transfer genes between species
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Which two enzymes are used to insert genes into plasmids in gene transfer?
Restriction endonucleases & DNA ligase
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What does Restriction endonucleases do in gene transfer?
cuts DNA molecules at specific base sequences
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What does DNA ligase do in gene transfer?
makes sugar-phosphate bonds link to nucleotides together & form continuous strands of nucleotides
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What is a recombinant plasmid?
A plasmid with a gene from another species inserted
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Outline the transfer of the human insulin gene into bacteria (Steps 1-5)
1)human pancreas mRNA coding insulin extracted, 2)DNA copies of mRNA made using enzyme reverse transcriptase, 3)Extra G nucleotides added to gene ends-makes sticky, 4)E.Coli Plasmid cut open 5)Extra C nucleotides added to plasmid ends-makes sticky
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Outline the transfer of the human insulin gene into bacteria (Steps 6-
6)Insulin gene &plasmid mixed (linked by complementary base pairing) 7)DNA ligase seals up nicks in DNA 8)Plasmids mixed w/ host cells (e.coli) which absorbs them 9)Gm e.coli cultured in a fermenter 10)E.coli makes human insulin> extracted & purified
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What is Bt toxin
a bacterial protein which kills insect pest which feed on crops (corn borers). This protein is code from the bacteria Bacillus Thruingiensis
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Potential benefits of Bt maize (3)
1.Higher crop yields: more food due to less pest damage, 2.Less land needed for crop production- some areas could become wildlife conservation areas, 3.Less insecticide used- expensive &harmful to workers & wildlife.
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What qualities are being produced in some gm crops (6)
herbicide resistance, increased vitamin content, decreased allergen/toxin content, resistance to virus diseases, increased tolerance to drought, cold or saline soils & increased shelf life
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Possible harmful effect of Bt maize
Nonpest insects killed- Maize pollen blown onto wild plants eaten by insects (monarch butterfly) 2> Transferred gene may spread to wild plant populations by cross-pollination> makes them toxic to insects .Corn pests may devlop Bt toxin resistance
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Clone
a genetically identical organism derived from a single original parent
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Cloning
the production of an organism that is genetically identical to another organism
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Somatic-cell nucleus transfer
Method of cloning animals with know characteristics- nucleus from egg cell is removed & replaced by a nucleus of a differentiated somatic (body) cell.
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What is the simplest way to clone an animal
break up an embryo into more than one group of cells (at early stage when it consists entirely of embryonic stem cells)
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Outline the cloning of adult animals using differentiated cells, using dolly the sheep as example (5)
1.Donor udder cell taken &cultured in lab for 6 days, 2.Unfertilised egg taken from another sheep- nucleus removed. 3.Egg fused w/ donor cell using electricity pulse, 4.Embryo transferred into 3rd sheep (surrogate)-gives birth>identical to 1rst sheep
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What are stem cuttings?
short lengths of stem that are used to clone plants artifically
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Conditions needed for stem cuttings (3)
Compost must be well-aerated & moisture retentive, .Cutting cut just below a node, . Clear plastic bag around cutting increases humidity & decrease transcription
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What could be the independent variables of stem cuttings (4)
How many leaves left on the cutting, whether hormone protein powder was used, how warm cutting is kept & whether plastic bag is over the cutting
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What could be the dependent variable of stem cuttings
Whether any roots formed or not
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Metaphase 2
Chromosomes line up across the equator, new spindle microtubles attach to chromosomes vie centromere
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What are the stages of meosis? (8)
Prophase 1, Metaphase 1, Anaphase 1, Telophase 1+cytokinesis Prophase 2, Metaphase 2, Anaphase 2, Telophase 2+cytokinesis
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What are the causes of genetic variation? (3)
Mutation, sexual reproduction, meosis
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Card 2

Front

Properties of eukaryotic chromosomes (4)

Back

1) contains linear DNA molecule 2) associated with histone proteins 3) no plasmids 4) two or more chromosomes

Card 3

Front

Properties of prokaryotic chromosomes (4)

Back

Preview of the front of card 3

Card 4

Front

Autoradiography

Back

Preview of the front of card 4

Card 5

Front

Steps of autoradiography

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Preview of the front of card 5
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