Presentation on theme: "Natural Selection Is the process by which organisms that are better adapted to their environment survive and breed while those less well adapted fail to."— Presentation transcript:
1 Natural SelectionIs the process by which organisms that are better adapted to their environment survive and breed while those less well adapted fail to do so.The better adapted organisms are more likely to pass their characteristics to succeeding generations.
2 A wee story to set the scene.. Mice are not genetically identical. They areproduced by sexual reproduction whichensures that they possess differentcombinations of genes from their parents.Important characteristics such as coat colourand thickness, speed and reactions, foodfinding ability, resistance to disease andaggressiveness will vary from mouse to mouse.
3 Only those mice with the best combinations of genes for their habitat will survive. Thismeans that their gene combination will bepassed on to their offspring. Mice withless useful combinations of genes die andso these genes are not passed on.This is the story of natural selection and ifit operates over millions of years then it isthought that it can give rise to new species.
4 Natural Selection in the Peppered Moth The peppered moth is a nocturnal insect which rests duringthe day on tree trunks. Insect-eating birds prey on theresting moths by picking them from the tree trunks.In the early 19th century, the moths were well adapted tosurvive as they had light–coloured speckled wings whichcamouflaged them against the lichen covered tree trunks.This meant that the birds could not see them and it gavethe moths some protection.
5 There is another form of the peppered moth which is melanic – it is nearly all blackcoloured.(If these moths were on a lichen coveredtree such as the one in the picture, do youthink they would survive the beady eyes ofan insect-eating bird?)Melanic moths show up well against the lichen-covered trees and birds can easily hunt them.so melanic moths rarely survive and pass on theirgenes.
6 Environmental change and Natural Selection in the Peppered Moth During the late 19th century, Britain saw theIndustrial Revolution.Large towns and cities were formed wherefactories and industries burned up largevolumes of coal to power them.Burning the coal caused lots of sooty smokeand sulphur dioxide.
7 As you know, lichens are very sensitive to pollution and so will not grow in polluted areas.The trees became less lichen-covered and morecoated with black soot.Which moths would be more camouflaged now?(The melanic form or the light speckledform?)Which form would have the greatest survival and increasein number and pass on their genes to future generations?Which form would die out and not be able to pass on theirgenes?
8 Lichen-covered tree trunk in unpolluted area Soot-covered tree trunk invery polluted areaToday, due to the Clean Air Act, the pale form of moth is becoming more numerous again in what were once polluted areas. Perhaps the situation we had before the Industrial Revolution will return one day?
10 Selective BreedingSo far we have looked at natural selection and how this has led to the great biodiversity found today.We are now going to look at Selective Breeding where humans deliberately choose which individuals to breed. This can happen in both plants and animals.
11 Selective Breeding in Domesticated Animals Humans deliberately breed desirable characteristics so that the offspring will also show these characteristics.Over time and several generations later, an improvement may result.However, it takes quite a long time and the results are not always guaranteed.
12 Example: cows and milk yield Farming is a huge industry in Britain today.It would not be cost effective to our farmers if only some of their cows produced large volumes of milk.So, they will only breed cattle with desirable characteristics (large milk yield). The aim is that the female offspring should be able to produce large quantities of milk.
13 Draw a line graph of the milk yields in cattle from Selective Breeding YEARAverage yield (litres per cow per year)1905190019202300193527001950340019804700Title: Milk Yields in CattleAverage yieldYear
14 More Examples of Selectively Bred Animals Characteristics Selected ForCattleMilk and Beef productionSheepMilk and Wool qualityPigsGrowth rate and litter sizePoultryGrowth rate and egg productionHorsesStrength, size and speed
15 Selective breeding in plants In 1895 a group of American Biologists began a breeding experiment using a variety of maize (sweet corn) whose seed grains varied slightly in oil and protein content.Firstly they selected only those plants that produced seed grains with the highest oil content – strain O.Then they selected only those plants that produced seed grains with the highest protein content – strain P.They repeated this over 50 generations. Strain O showed improved oil content and strain P showed improved protein content.
17 Limitations of Selective Breeding Relies on sexual reproduction- fertilisation not always guaranteed and there may be difficulties getting individuals to breed.- can take months or even years to get just one generation so can be very slow.
18 Limitations of Selective Breeding…. Inbreeding is a common method used in selective breeding.- can lead to an increase in recessive genes.- since many of these normally hidden recessive genes give inferior qualities, inbred lines may show disadvantages.
19 Limitations of Selective Breeding Individuals may not have the genes for the desired characteristic.- If they are not present, they cannot be created e.g. if a gene for disease resistance does not exist in a species then the characteristic cannot be developed in this way.
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