Mendelian Inheritance in Drosophila

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Lab#3
Mendelian Inheritance in Drosophila
Lab Report 1

In this experiment we are investigating the strength of the ratios discovered by Gregor Mendel in both the monohybrid and dihybrid cross. The ability to test these ratios stems from the use of Mendel’s law of segregation which states that during meiosis allele pairs will separate in gametes so one of each allele is present in a gamete. (Garey, et al,pg 8-13) These single alleles are then combined with the other parental gamete forming a new somatic cell. Another important law is the law of independent assortment which means that different gene pairs will separate independently of each other allowing two traits to be monitored at once. With these laws, ratios can be assigned to both the Monohybrid, a cross of only one gene, and a dihybrid cross, a cross of two independent genes, which will result in ratios for both phenotype and genotype. The phenotypic ratio for a standard F1 monohybrid cross is 1:2:1 while a dihybrid cross has a phenotypic ratio of 9:3:3:1. The genotypic ratio of for a monohybrid cross though is 3:1 as the dominant allele will generally over power the recessive allele. The only cases where this doesn't happen is when the alleles show codominance and a blending effect takes place. The use of Drosophila melanogaster is very useful when trying to observe many genetic properties, due to the ability to distinguish between each phenotype. This is due to the clear sex linked genes that are easily expressed and don't result in sterile or deceased offspring and the genes that are located on different chromosomes so that no crossing over occurs. Also the time between generations is exceptionally short allowing for a generation of flies to be produced almost every week. These flies can be easily secured and taken care of in a lab environment making them perfect for genetic studies. From this we can hypothesize that the ratio’s set up by Mandel will be shown in the monohybrid cross, the

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