28/05/13VariationVariation“Variation” is the name given to differences betweenindividuals of the SAME species.Variation is due to GENETIC or ENVIRONMENTAL causes.For example, consider identical twins:1) Ways in which Tom andJames are the same (causedby genes):2) Ways in which Tom andJames are different (causedby environment):
28/05/13Where is this information stored?Where is this information stored?Section of a chromosome:Genes foreye colourGenes forhair colourGenes forblood group:Different species have different numbersof chromosomes. Humans have 46 (23pairs) in every cell.
28/05/13Sexual ReproductionSexual ReproductionThe human eggand sperm cell(“GAMETES”)contain 23chromosomeseach.When fertilisation happens thegametes fuse together to makea single cell called a ZYGOTE.The zygote has 46chromosomes (23 pairs).
28/05/13Sexual vs. Asexual reproductionSexual vs. Asexual reproductionSexual reproduction:•2 parents are needed•Offspring will have “pairs” of chromosomes•This will cause genetic variationAsexual reproduction:•Only 1 parent needed•Offspring are genetically identical to parent (“clones”)
28/05/13MitosisMitosisEach daughter cell hasthe same number ofchromosomes and geneticinformation as the parent.
28/05/13MeiosisMeiosisEach daughter cell has halfthe number of chromosomesof the parent.
28/05/13Mitosis vs. MeiosisMitosis vs. MeiosisMitosis:1. Used for growth and repair ofcells2. Used in asexual reproduction3. Cells with identical number ofchromosomes and geneticinformation are producedMeiosis:1. Used to produce gametes forsexual reproduction2. Each daughter cell has half thenumber of chromosomes of theparent
28/05/13FertilityFertilityThe events that happen in a female body during the menstrualcycle are triggered by hormones (chemical messengers).Artificial hormones can be used to:In normal circumstances naturalhormones are responsible for releasingthe egg and for thickening the lining ofthe womb. These hormones areproduced by the pituitary gland in thebrain and in the ovaries.1) Stimulate the release of eggs(fertility treatment)2) Inhibit the release of eggs(contraceptive pills)
28/05/13FertilityFertility3 hormones are involved in the menstrual cycle: oestrogen, LH and FSH.Here’s how:Step 3: LHstimulates therelease of themature egg inthe middle ofthe menstrualcycleArtificial fertility:1) To INCREASE fertility FSH is given to stimulate maturation of eggs.2) To DECREASE fertility oestrogen is given (“The Pill”) to inhibit FSHproduction stopping eggs from maturing.Step 1: FSHproduced by thepituitary glandcauses both an eggto mature and theovaries to startproducing oestrogenStep 2: The rising levels ofoestrogen cause the pituitarygland to stop producing FSHand produce LH instead
28/05/13Key wordsKey wordsGameteZygoteAlleleDominantRecessiveHomozygousHeterozygous•This allele determines the development of acharacteristic•This is formed when an egg is fertilised by a sperm•This allele will determine a characteristic only ifthere are no dominant ones•This word refers to a pair of chromosomes beingmade of two different alleles of a gene•An egg or a sperm are called this•This word refers to a pair of chromosomes beingmade of two of the same alleles of a gene•An alternative form of a gene
28/05/13Genes, Chromosomes and DNAGenes, Chromosomes and DNA
28/05/13Some facts:- Made up of paired bases- Contain instructions on what a cell does, how the organismshould work etc- The instructions are in the form of a code- The code is made up from the four bases that hold thestrands together- The bases represent the order in which amino acids areassembled to make proteins- Each group of 3 bases represents one amino acid- There are only about 20 amino acidsHow genes workHow genes work
28/05/13Boy or Girl?Boy or Girl?X Y XXX XYGirl Boy“Allele”
28/05/13FatherMotherSonDaughterBoy or Girl?Boy or Girl?
28/05/13Eye colourEye colourIn eye colour the brown eye allele is dominant, so we call itB, and the blue eye is recessive, so we call it b:bbBB BbHomozygousbrown-eyedparentHeterozygousbrown-eyedparentBlue-eyed parentWhat would the offspring have?
28/05/13Eye colourEye colourExample 1: A homozygousbrown-eyed parent and ablue-eyed parent:Example 2: 2 heterozygousbrown-eyed parentsBB bbX Bb BbXParents:Gametes:Offspring: Bb Bb BbBb BB Bb bbbBB B bb B bB b(FOIL)All offspring have brown eyes 25% chance of blue eyes
28/05/13Eye colourEye colourExample 3: A heterozygous brown-eyedfather and a blue-eyed mother:BbBb Bb bbbbbbb bB bEqual (50%)chance ofbeing eitherbrown eyed orblue eyed.
28/05/13B bbbAnother methodAnother methodExample 3: A heterozygous brown-eyedfather and a blue-eyed mother:B bb Bb bbb Bb bbFatherMother
28/05/13Example questionsExample questions1) In mice, white fur is dominant. What type of offspringwould you expect from a cross between a heterozygousindividual and one with grey fur? Explain your answer with agenetic diagram.2) A homozygous long-tailed cat is crossed with a homozygousshort-tailed cat and produces a litter of 9 long-tailed kittens.Show the probable offspring which would be produced if twoof these kittens were mated and describe the characteristicsof the offspring (hint: work out the kitten’s genotype first).
28/05/13Inherited diseasesInherited diseases1) Cystic fibrosis (1 in 2000)– a disease that causes thick and sticky mucusto coat the lungs, gut and pancreas. It’s caused by recessive alleles:2) Huntingdons disease (1 in 20,000)– a disease of the nervous systemthat causes shaking and eventually dementia. It’s caused by a dominantallele:3) Sickle cell anaemia – a disease that alters the shape of red blood cells,thereby reducing their oxygen capacity, causing weakness and anaemia.It’s caused by recessive alleles:Ff FfXCc ccXSs SsX
28/05/13MutationsMutationsMutations are changes in the structure of the DNA molecule. They can bepassed on to daughter cells through cell division. They will result in thewrong proteins being produced.Mutations can be caused by:- Ionising radiation (UV, X-rays etc)- Radioactive substances- Certain chemicalsEffects:- Mostly harmful- Causes death or abnormality in reproductive cells- Causes cancer in body cells- Some CAN be neutral or even beneficial (e.g. the peppered moth)
28/05/13Modern GeneticsModern GeneticsMy name is Gregor Mendel. I am thefather of modern genetics because ofthe work I did on pea plants in 1865…Take two plants; one which ispure-bred for tallness and onepure-bred for shortness, andcross them:XMendel’s experiment:
28/05/13Modern GeneticsModern GeneticsAll the plants producedwere tall.Now cross two of these plants…3 out of every 4 plantswere tall, leading Mendelto hypothesise that “forevery characteristicthere must be twodeterminers”
28/05/13ClonesClonesPlants can reproduce ASEXUALLY. The offspring aregenetically ________ to the parent plant and are called_________. Two examples:1) This spider plant has grown a rootingside branch (“stolon”) which willeventually become __________.2) A gardener has taken cuttings ofthis plant (which probably has goodcharacteristics) and is growing themin a ____ atmosphere until the____ develop.Words – clones, damp, independent, roots, identical
28/05/13Selective breedingSelective breedingI raise cows. Each type ofcow is good at a certain job.The Friesian cow produceslarge quantities of milk, theJersey cow produces verynice milk and the Herefordcow produces lot of beef.If, for example, I want lotsof milk I would only breedFriesian cows with eachother – this is SELECTIVEBREEDING.FriesianJerseyHereford
28/05/13Selective breeding vs. CloningSelective breeding vs. CloningAdvantages DisadvantagesCloningSelectivebreeding
28/05/13Selective breeding vs. CloningSelective breeding vs. CloningAdvantages DisadvantagesCloning1) Allows largenumbers oforganisms with goodcharacteristics tobe produced2) Very efficient1) Causes reducednumbers of alleles2) Loss of variationcould harm survivalchances if theenvironment changesSelectivebreeding1) Produced organismswith favouredcharacteristics2) Very efficient andeconomically viable1) Causes reducednumbers of alleles2) Loss of variationcould harm survivalchances if theenvironment changes
28/05/13Genetic ModificationGenetic ModificationPossible uses of genetic modification of organisms:-Improving crop yield-Improving resistance to pesticides-Extend shelf-life-Manufacture a certain chemical (e.g. insulin)-Convenience
28/05/13Genetic engineeringGenetic engineeringInsulin is a hormone produced by the pancreas to help controlblood sugar levels. Diabetics can’t produce enough insulin andoften need to inject it.Insulin can be made by genetic engineering:
28/05/13Genetic engineering - InsulinGenetic engineering - InsulinStep 1: Using RESTRICTIONENZYMES “cut out” the part ofthe human chromosome that isresponsible for producing insulin.Step 2: Using another restrictionenzyme cut open a ring of bacterialDNA (a “plasmid”). Other enzymesare then used to insert the piece ofhuman DNA into the plasmid.Step 3: Place the plasmid into a bacteriumwhich will start to divide rapidly. As itdivides it will replicate the plasmid andmake millions of them, each with theinstruction to produce insulin. Commercialquantities of insulin can then be produced.
28/05/13EvolutionEvolutionCharles Darwin (1809-1882)
28/05/13EvolutionEvolutionEvolution is the slow, continual change oforganisms over a very long time. Allliving things on the Earth havedeveloped from the first simple lifeforms that arrived 3,000,000,000 yearsago.One of the effects of evolution is that species will becomebetter adapted to their environment. If these speciesdon’t adapt they may become extinct due to being unable todeal with any of these factors…1) Increased competition2) Changes in the environment3) New diseases4) New predators
28/05/13EvolutionEvolutionMy key observations:1) All living things produce moreoffspring than survive to adulthood2) In spite of this, population sizesremain roughly constant3) Variation exists among species4) Characteristics can be passed onfrom one generation to the next.These observations led me to theconclusion that species evolve over aalong period of time by a mechanismcalled “Natural Selection”. The mainevidence for this is from fossilrecords.
28/05/13Natural SelectionNatural Selection1) Each species shows variation:2) There is competition within eachspecies for food, living space,water, mates etc4) These survivors will pass on theirbetter genes to their offspring whowill also show this beneficial variation.Get offmy landGutted!Yum3) The “better adapted” members ofthese species are more likely tosurvive – “Survival of the Fittest”
28/05/13A smaller example…A smaller example…Consider the four steps of natural selection in the example ofsome bacteria that has become resistant to penicillin:1) Variation – some strains of bacteriaare resistant and some aren’t.2) Competition – The non-resistantbacteria are killed by the penicillin.3) Survival of the fittest – theresistant bacteria survive.4) Passing on of genes – the resistantbacteria reproduce and pass ontheir adaptations to theiroffspring.BacteriaPenicillin