Genetics SL PDF

Inheritance  Genes  Chromosomes  Inheritance  Genetic modification and biotechnology  Genes  A GENE is a heritable factor that consists of a length of DNA and influence a specific characteristic.  A gene occupies a specific position on one type of c...

Inheritance  Genes  Chromosomes  Inheritance  Genetic modification and biotechnology  Genes  A GENE is a heritable factor that consists of a length of DNA and influence a specific characteristic.  A gene occupies a specific position on one type of chromosome.  Genes are organised into CHROMOSOMES.  Some genes have more than one form (alleles).  An ALLELE is a specific form of a gene differing from other alleles by one or a few bases.  Alleles of the same gene occupy a corresponding place (LOCUS) on each chromosome.  GENOME – the complete set of an organism’s base sequences  https://www.youtube.com/watch?v=BQQEX8rU2tY  Chromosomes  CHROMOSOMES- bundles of long strands of DNA  https://www.youtube.com/watch?v=tsVHWbXqum8 https://www.youtube.com/watch?v=IePMXxQ-KWY Mutations  A mutation is a random, rare change in genetic material.  E.g. Change in the sequence of bases Thymine replaces Adenine in base sequence.  Corresponding bases along mRNA are altered during transcription. Base substitution mutation  Changing ONE BASE results in different amino acid placed in polypeptide chain.  May have little or no effect on organism or may have major influence on physical characteristics (eye colour, number of legs, number and shape of wings etc.)  A mutation sometimes found in gene which creates haemoglobin for red blood cells in humans.  This mutation gives a different shape to the haemoglobin molecule and ultimate the shape of the red blood cell (sickle shaped cells). Sickle cell anaemia  Caused by a base substitution mutation.  One base is substituted for another.  Codon GAG becomes GTG.  During translation VALINE is added instead of GLUTAMIC ACID  Different shape of valine MODIFIES (changes) shape of resulting polypeptide chain.  Haemoglobin molecule shape and red blood cell shape changed (sickle shaped) Theoretical Genetics  Gregor Mendel, Austrian monk  Published results of his experiments with garden peas in 1865  “factors” not “genes”  Role that DNA played not discovered  Used artificial pollination  Eliminates role of chance  Results of TALL plants with SHORT plants = TALL plants  TALL plants with each other resulted in some SHORT plants Key terminology  GENOTYPE – symbolic representation of a pair of alleles possessed by an organism, represented by two letters E.g. Bb, GG, Ll  PHENOTYPE- The characteristics or traits of an organism E.g. Tall, yellow flowers, Black fur  DOMINANT ALLELE– Always expressed in the phenotype , has the same effect on the phenotype whether it is paired with the same allele or a different one  E.g the genotype Aa gives the dominant A trait because the a allele is not expressed (masked) Key terminology RECESSIVE ALLELE – An allele that has an effect on the phenotype only when present in the homozygous state E.g. aa gives rise to the recessive trait because no dominant allele is there to mask it  CODOMINANT ALLELES – Pairs of alleles that BOTH affect the phenotype when present in a heterozygote E.g. straight + curly hair = different degrees of hair curliness (both alleles influence hair condition) Key terminology  LOCUS – The particular POSITION of a gene on homologous chromosomes Key terminology  HOMOZYGOUS – Having two identical alleles of a gene E.g. AA and aa  HETEROZYGOUS – Having two different alleles of a gene (paternal allele different form maternal allele) E.g. Aa Monohybrid Genetic Cross  Parental phenotype  Parental genotype  Gametes  Punnett Grid (Square) (F1 generation)  F2 generation Multiple Alleles  The ABO blood type system in humans has four possible phenotypes: A, B, AB and O.  To create these 4 blood types there are 3 alleles of the gene  , , i (Alleles for type A, B and O blood)  These 3 alleles can produce 6 different genotypes  Crossing these together in all possible combinations creates 6 genotypes which give rise to the 4 phenotypes (blood groups)  Type A blood - ,  ,  (codominance)  Type O blood- ii Genetic Modification  a technique to change the characteristics of a plant, animal or micro-organism by transferring a piece of DNA from one organism to a different organism  Gene Transfer -technique of taking a gene out of one organism (donor organism) and placing it in another (host organism) Genetically modified organisms  An organism that has had an artificial genetic change using genetic engineering techniques. Gene transfer  Arctic fish cold resistant gene transferred to tomatoes to make them resistant to cold and frost.  Gene for pest-killing toxin transferred from soil bacteria (Bacillus thuringiensis ) to corn to form Bt-corn Arctic fish cold resistant gene transferred to tomatoes to make them resistant to cold and frost. Gene for pest-killing toxin transferred from soil bacteria (Bacillus thuringiensis ) to corn to form Bt-corn Transgenic Plants (Crops)  Removal of undesirable genes or insertion of more desirable genes.  “Flavr Savr” tomato – genetically modified to delay ripening and rotting process to stay fresher for longer.  another species of tomato was modified to make it more tolerant to higher levels of salt in the soil.  Claims : GM foods could help solve the problem of world hunger by allowing farmers to grow foods in various otherwise unsuitable conditions.  Critics: problem of world hunger is one of food distribution, not food production  Genetically modified rice (yellow rice) – engineered to produce beta carotene in the rice grains prevents Vit.A deficiency in people eating the rice. Transgenic animals  To get animals to produce a substance which can be used in medical treatment.  Lack of protein called factor IX – blood does not clot  Transgenic sheep used to produce protein (factor IX) in their milk  Future genetic modifications could include: inserting genes to make animals more resistant to parasites, to make sheep produce pre-dyed wool of any colour, to produce prize-winning show dogs, faster racehorses Genetic engineering: Good or Bad?  Some benefits, promises and hopes for the future include:  GM crops can improve food production  GM crops which produce their own pest-control substances- beneficial to environment- fewer chemical pesticides needed  Using GMO to produce rare proteins for medications or vaccines could be in the long run less costly and produce less pollution  farmers can be more in control of what crops or livestock they produce- quicker than selective breeding  GM plants can reduce hunger by farmers using pest/ drought –resistant crops in developing nations Harmful effects, dangers and fears  No one knows the long-term effect of GMOs in the wild (difficult to keep GM plants under control, gene integration into wild species)  Genes could cross species- no one knows the consequences of genes crossing species  Bt-crops could be harmful to humans  Risks for allergies (unclear food labelling)  Small number of corporations will control large portions of human food supply.  High-tech solutions not necessarily better than simple solutions (educate farmers about alternative farming methods and pest control)  Proliferation of GMO may lead to a decrease in biodiversity