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Investigate patterns of inheritance for a single characteristic such as body colour of Drosophila Melanogaster and examine Mendel's laws of dominance and segregation.

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Introduction

Contents General Introduction 3 Monohybrid Cross 3 Aims and Objectives 3 Introduction 3 Materials and Methods 5 Results 7 Discussion and Conclusions 10 Aims and Objectives 11 Introduction 11 Materials and Methods 12 Results 12 Discussion and Conclusions 16 X Linked Cross 17 Aims and Objectives 17 Introduction 17 Materials and Methods 18 Results 18 Discussion and Conclusions 21 References 22 Appendix 1 23 General Introduction The following report investigates Mendel's Laws and patterns of inheritance using Drosophila Melanogaster in 3 types of crosses. Monohybrid Cross Aims and Objectives To investigate patterns of inheritance for a single characteristic such as body colour of Drosophila Melanogaster and examine Mendel's laws f dominance and segregation. Introduction Gregor Mendel was an Austrian monk whose work on the inheritance of traits of pea plants in the 1860s, although not initially recognised, sets the foundation of genetics. Mendel developed what are now known as Laws of inheritance. Mendel examined specific characteristics of the pea plant, Pisum sativum. Such variations of characteristics are known as traits. Over many generations of selective cross pollination of this pea plant Mendel discovered that certain traits would show in offspring without, what he called, blending of parental characteristics. For example with flower colour, it is either purple or white, not any intermediate colour. He discovered that there were 7 of these such traits which were apparent in one of two forms: This discovery proved other theory's of the time such as the blending theory to be incorrect. Mendel was able to cross pollinate purebred plants. That is plants with particular traits. Mendel found when cross pollinating plants which produce yellow seeds with those that produced green seeds that all of the first generation offspring produced yellow seeds. On further crossing this generation he found that 3:1 ratio of yellow seed producing plants to green seed producing plants occurred. This type of cross, when a single characteristic or trait is being examined is now known as a monohybrid cross. ...read more.

Middle

The analysis shows a probability of 0.966, which means that there is a 96.6% chance that the variation is due to random error and therefore the hypothesis can be accepted. There is a genotypic ratio of 1:2:1, homozygous dominant: heterozygous : homozygous recessive, confirming predictions made. The two sets of results give further evidence of Mendel's law of segregation. To determine definitively the genotypic ratio for the F2 generation further investigation or back crosses would need to be performed. Dihybrid Cross Aims and Objectives To further investigate Mendel's laws of dominance and segregation through examination of more than one trait simultaneously, i.e. a dihybrid cross. To investigate Mendel's third law, the law of independent assortment. Introduction During the course of Mendel's work with monohybrid crosses, he noticed that none of the single traits seemed to affect the other in inheritance, i.e. a tall plant did not always have purple flowers, etc. The different traits appeared to be inherited independently. In modern terms this theory states that different pairs of alleles are passed to offspring separately and as a result genes are present in offspring that are not in the parents, recombinants. This gave ratios of 4 phenotypes instead of two and in the ratio of 9:3:3:1 and a genotypic ratio of 1:2:2:1:4:1:2:2:1. It has since been discovered that the loci of the genes is vital to this kind of inheritance. The closer together genes are on a chromosome the more likely they are to be linked and therefore inherited together. Looking at the diagram below it can be seen how gametes segregate in dihybrid crosses, during meiosis. Materials and Methods The method was as per the monohybrid cross with the exception that the parental (initial) cross was set up thus: 5 Male ebony bodied, x 5 Female Wild type bodied wild type winged flies vestigal wings Again, these flies were homozygous for each particular allele they posses at each of the two gene loci. ...read more.

Conclusion

Ratio Wild eye colour male 39 52 1 Wild eye colour females 36 48 1 White eye colour male 0 0 0 White eye colour female 0 0 0 Class Results: Group 1 2 3 4 5 6 7 8 9 10 11 Total Phenotype Wild eye colour male 62 109 39 100 55 58 77 52 35 67 39 693 Wild eye colour female 55 112 36 87 55 83 84 25 40 61 67 701 White eye colour male 0 0 0 0 0 0 0 0 0 0 0 0 White eye colour female 0 0 0 0 0 0 0 0 0 0 0 0 The Chi square (c2) analysis Phenotype Observed Number Expected Number Chi Square (c2) Probability WT Eye Male 1015 1019 0.859344 0.835226 WT eye Female 1023 1019 White eye Male 0 0 White eye Female 0 0 Discussion and Conclusions The results for the first cross, white eyed females with wild type males, showed the all the males in the F1 generation showed the white eyed trait and none of the females did. This suggests that the allele is recessive and X linked. The chi square analysis gave a probability of 0.999 again a 99.9% chance that this hypothesis s correct. It also suggests that the error involved is down to random error. Eight flies were counted to have the phenotype of wild type eye and male. This figure could be due to human error in identification of phenotype or sex or could be due to random mutations of the gene. The results for the second cross show that none of the flies showed the white eye trait giving more evidence that the allele for the trait is indeed recessive and X-linked. The statistical analysis gave a probability of 0.835. This shows that there is 83.5% chance that the hypothesis is correct. This basis it would be recommended that the hypothesis not be rejected but that further investigation should be carried out. It is studies in this particular areas of genetics that are vital to the control, diagnosis and curing of disease such as Haemophila. ...read more.

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