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Environmental Biology Genetics

Monday, April 02, 2012. 2. Mr G Davidson. Alleles. Genes control the characteristics of an organism, e.g. flower colour in peas.Alleles are different forms of the same gene.An allele is a different form of that gene, e.g. red flower or white flower.. Monday, April 02, 2012. 3. Mr G Davidson. Exam

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Environmental Biology Genetics

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    1. Environmental Biology & Genetics Genotype & Phenotype

    2. Monday, April 02, 2012 2 Mr G Davidson Alleles Genes control the characteristics of an organism, e.g. flower colour in peas. Alleles are different forms of the same gene. An allele is a different form of that gene, e.g. red flower or white flower.

    3. Monday, April 02, 2012 3 Mr G Davidson Examples of alleles

    4. Monday, April 02, 2012 4 Mr G Davidson Alleles Most genes normally have at least 2 forms. (Some have more than 2) Each body cell contains 2 alleles for every characteristic. This is because the cell contains 2 of each type of chromosome and the alleles are found at the same place on each of the two chromosomes.

    5. Monday, April 02, 2012 5 Mr G Davidson Alleles

    6. Monday, April 02, 2012 6 Mr G Davidson Alleles When gametes (sex cells) are being formed, the pair of chromosomes will be split up, each gamete only getting one chromosome. E.g.

    7. Monday, April 02, 2012 7 Mr G Davidson Alleles This means that when one gamete fertilises another, the resulting zygote will have 2 alleles, one from each gamete. The appearance of the organism depends on which of the alleles is dominant or recessive.

    8. Monday, April 02, 2012 8 Mr G Davidson Alleles A dominant allele will always show up in the appearance of an organism. A recessive allele will only show up if it is paired with another recessive allele. When describing an allele, for convenience, we usually give it a symbol, generally the first letter of the dominant allele.

    9. Monday, April 02, 2012 9 Mr G Davidson Alleles If it is dominant it gets the capital letter and if it is recessive it gets the lower case of the same letter. E.g. in pea plants tall is dominant over dwarf, and so the tall allele is given the letter T, and the dwarf allele the letter t. The genotype of the organism is the alleles it carries for that particular characteristic.

    10. Monday, April 02, 2012 10 Mr G Davidson Alleles TT is a genotype and the plant will be tall. Tt is a genotype and the plant will be tall, because the T is dominant over the t. tt is a genotype and the plant will be dwarf. What the plant actually looks like (how the genes are expressed) is called its phenotype.

    11. Monday, April 02, 2012 11 Mr G Davidson Genotypes & Phenotypes If both alleles are the same in the genotype of an organism, it is said to be true-breeding or homozygous, i.e. TT or tt. If the alleles are different in the genotype of the organism, it is said to be heterozygous, i.e. Tt.

    12. Monday, April 02, 2012 12 Mr G Davidson Genotypes & Phenotypes

    13. Monday, April 02, 2012 13 Mr G Davidson Monohybrid Inheritance In pea plants, red flower colour (R) is dominant to white flower colour (r). If we were to cross a homozygous red plant with a white plant, we would set the cross out as follows:

    14. Monohybrid Inheritance To find out which characteristic is dominant we carry out a test cross. We cross true breeding (homozygous) strains of the two alleles. We refer to the first generation as the P (parent) generation and the resulting generations as F1 and F2 (first and second filial generations) Monday, April 02, 2012 Mr G Davidson 14

    15. Monday, April 02, 2012 15 Mr G Davidson Monohybrid Inheritance

    16. Monohybrid Inheritance To complete the test cross the F1 generation are allowed to breed together producing a ratio of 3 dominant : 1 recessive trait This is split up into: 1 dominant homozygous:2 dominant heterozygous :1 recessive homozygous. Monday, April 02, 2012 Mr G Davidson 16

    17. Monohybrid Inheritance Monday, April 02, 2012 Mr G Davidson 17

    18. Monday, April 02, 2012 18 Mr G Davidson Monohybrid Inheritance This type of inheritance was first studied in the 19th Century by an Austrian monk called Gregor Mendel. He only studied one clear characteristic at a time in breeding experiments which we call crosses. The crosses are worked out using a Punnett square. E.g. in mice black coat colour is dominant over albino.

    19. Monday, April 02, 2012 19 Mr G Davidson Monohybrid Crosses

    20. Monday, April 02, 2012 20 Mr G Davidson Monohybrid Crosses

    21. Monday, April 02, 2012 21 Mr G Davidson Monohybrid Inheritance We can then identify the genotype of individuals who have black fur by back-crossing them with albino mice. This is called a test backcross and would look like the following.

    22. Monday, April 02, 2012 22 Mr G Davidson Monohybrid Crosses

    23. Monday, April 02, 2012 23 Mr G Davidson Monohybrid Crosses Your answer should always have the parental genotypes. Your answer should always have the parental gametes. Your answer should always have a completed punnett square. Your answer should always have the F1 phenotypes and the ratio they occur in.

    24. Monday, April 02, 2012 24 Mr G Davidson Family Trees Family tree diagrams can be used to show the transmission of alleles over a number of generations. The following family tree shows how the “ability to roll the tongue” allele is transmitted through 3 generations.

    25. Monday, April 02, 2012 25 Mr G Davidson Family Trees

    26. Monday, April 02, 2012 26 Mr G Davidson Family Trees

    27. Monday, April 02, 2012 27 Mr G Davidson Co-Dominance It is possible for 2 alleles to have the same level of dominance, and in this case they are said to be co-dominant. In this case the offspring usually have a phenotype consisting the characteristics of both parents. E.g. If red and a white short horn cattle are crossed, the offspring has red and white hairs, resulting in a roan cow (looks pinkish).

    28. Monday, April 02, 2012 28 Mr G Davidson Co-Dominance

    29. Monday, April 02, 2012 29 Mr G Davidson Variation There are 2 types of variation shown in organisms: Discontinuous variation Continuous variation

    30. Monday, April 02, 2012 30 Mr G Davidson Variation Discontinuous variation shows distinct clear-cut differences, and is controlled by only one gene. Discontinuous variation is usually displayed in a bar chart.

    31. Monday, April 02, 2012 31 Mr G Davidson Discontinuous Variation

    32. Monday, April 02, 2012 32 Mr G Davidson Discontinuous Variation

    33. Monday, April 02, 2012 33 Mr G Davidson Discontinuous Variation

    34. Monday, April 02, 2012 34 Mr G Davidson Variation Continuous variation shows a range of differences, and is controlled by more than one gene. These differences can usually be measured. Continuous variation is usually displayed in a histogram.

    35. Monday, April 02, 2012 35 Mr G Davidson Continuous Variation

    36. Monday, April 02, 2012 36 Mr G Davidson Continuous Variation

    37. Monday, April 02, 2012 37 Mr G Davidson Continuous Variation

    38. Monday, April 02, 2012 38 Mr G Davidson Environmental Impact The final phenotype of an organism is influenced by variation in the environment in which the organism lives. Identical twins have the same genotype but may differ because of: Diet (eating different food) Activities (if one exercises a lot) Climate (if one moves to another climate)

    39. Monday, April 02, 2012 39 Mr G Davidson Natural Selection Most organisms produce far more offspring than are able to survive. This leads to a struggle for survival and many offspring will die before reaching an age where they can reproduce.

    40. Monday, April 02, 2012 40 Mr G Davidson Natural Selection There are several reasons why offspring do not survive. Starvation Eaten by predators Disease Exposure

    41. Monday, April 02, 2012 41 Mr G Davidson Natural Selection The ones which survive often have a better phenotype, suited to the environment, and they can pass on their genes. This is called “survival of the fittest”.

    42. Monday, April 02, 2012 42 Mr G Davidson Natural Selection Examples of genes which can be advantageous include: Speed Aggression Resistance to disease Coat thickness Coat colour (better camouflage) Quicker reactions

    43. Monday, April 02, 2012 43 Mr G Davidson Natural Selection Only the organisms better adapted to survive in their environment go on to reproduce. This can lead to the appearance of a new species. This is called evolution.

    44. Monday, April 02, 2012 44 Mr G Davidson Peppered Moth The peppered moth is an excellent example of natural selection. It has a lightly speckled body colour which provides camouflage against lichens which grow on tree barks. This means the birds can’t see them.

    45. Monday, April 02, 2012 45 Mr G Davidson Peppered Moth There is also a black variety of the peppered moth. (MELANIC) The black moths are easily seen and eaten by the birds. However, during the industrial revolution, the burning of coal produced a lot of black sooty smoke.

    46. Monday, April 02, 2012 46 Mr G Davidson Peppered Moth This killed the lichens on the trees and turned them black. This allowed the black moths to be easily camouflaged, and so they survived to reproduce more black moths, and so the population of black moths increased rapidly. However, the speckled moth became easier for the birds to see, and so their numbers were quickly reduced.

    47. Monday, April 02, 2012 47 Mr G Davidson Peppered Moth This only happened in industrial areas where the pollution was at its highest. Today both types of moth survive in different areas and they can still interbreed. In large industrial areas the black (melanic) moth is more common. In rural areas the light speckled moth is more common.

    48. Monday, April 02, 2012 48 Mr G Davidson Peppered Moth Evolution has not yet caused these moths to become different species. Today, the Clean Air Act is reducing pollution, and this will reduce the numbers of the melanic moth. Natural selection allows the moths to survive where they are. Natural selection leads to Biodiversity.

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