Greenville Technical College



Mendelian Genetics of Corn IntroductionIn 1866, Gregor Mendel published a paper outlining the basic principles of inheritance. These principles are now identified as Mendelian laws of inheritance. The two laws are: the law of segregation and the law of independent assortment. The law of segregation refers to the separation of the two homologous chromosomes during anaphase I of meiosis. The two alleles of a gene controlling a particular trait segregate along with the chromosomes they are located on. Thus, this first law is applicable to monohybrid crosses, where alleles of a single trait are followed. Mendel observed a predictable phenotype ratio in the F2 progeny of all monohybrid crosses that he performed with garden pea. The second law of independent assortment applicable to dihybrid crosses, where alleles of two different genes, controlling two separate traits are tracked together. This law says that any allele of one trait can combine with any allele of the second trait in forming gametes during meiosis. Alleles located on separate pairs of chromosomes assort independent of each other. Again, he observed a predictable phenotype ratio in the F2 progeny of dihybrid crosses. Corn (Zea maize) is one of the most important food crops of the world. Because of its economic importance, the genetics of corn has been studied extensively. In corn, male flowers are located on the tassel at the top of the adult plant. Female flowers are borne in an inflorescence closer to where the leaves join the stems. The female inflorescence can have as many as 1000 individual flowers and each flower produces a long silk. Pollination occurs when pollen from male flowers fall on the silks of in individual flower and develop long pollen tubes that grow into ovaries of female flowers. Fertilization takes place deep within the female flowers and eventually the fertilized ovary forms a kernel. Thus, each kernel is a result of an independent fertilization event that took place between two unique male and female gametes. Each kernel, if allowed to germinate, gives rise to a new plant with unique combination of alleles.Corn is a diploid plant with 10 pairs of chromosomes. Inheritance of many traits in corn follows simple Mendelian principles. In this lab we will follow the inheritance of both seedling and kernel traits. In all crosses parents are true-breeding (homozygous) for the given trait.Genetics of Corn Seedlings: Monohybrid cross:Corn seedling height Corn seedling color Dihybrid cross:AB) Corn seedling height and seedling colorDay 1: Corn plantingMaterial needed:Corn seedPotting mixPots and traysStakesLight banksMethod:You will work with a partner for the entire corn lab. Each table? will plant ………………………… Add details here.Add 150 ml> of water to the potting mix bag. NlknklnLnjDay 2: Data collectionGenetics of Corn ears:In reality, genetics of corn kernels is somewhat complex. This exercise uses a simplified version to investigate inheritance of two traits of corn kernels: kernel color and kernel sweetness. In all crosses parents are true-breeding (homozygous) for the given trait.Monohybrid crosses:Corn kernel color Corn kernel sweetnessDihybrid cross: CD) Corn kernel color and kernel sweetnessEpistasis: Include results from the corn ear that had a modified ratio. ................
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