Barbara McClintock By Kalim Kassim and Tim Milsom

Prior Knowledge In 1938, Marcus Rhodes provided the first description of an unstable mutation, found by using maize. In 1938, Marcus Rhodes provided the first description of an unstable mutation, found by using maize. This resulted in a variegated phenotype which produces irregular patterns of pigmentation and pigment production. This resulted in a variegated phenotype which produces irregular patterns of pigmentation and pigment production. 2 genes caused this irregularity: the unstable allele by one gene and a dominant mutation by the second gene called Dotted. 2 genes caused this irregularity: the unstable allele by one gene and a dominant mutation by the second gene called Dotted.

Barbara Mclintock In the 1940’s and 1950’s, she showed that this irregularity was caused by genetic elements that moved or transposed from one locus to another. In the 1940’s and 1950’s, she showed that this irregularity was caused by genetic elements that moved or transposed from one locus to another. She studied the mosaic patterns of maize seeds and the inheritance of these patterns. She studied the mosaic patterns of maize seeds and the inheritance of these patterns. She found 2 new dominant genetic loci that she names Dissociatior (Ds) and Activator (Ac) She found 2 new dominant genetic loci that she names Dissociatior (Ds) and Activator (Ac)

Dissociator caused the chromosomes to break and effected neighbouring genes when the activator was present. Dissociator caused the chromosomes to break and effected neighbouring genes when the activator was present. Later, in 1948, she found that Ds and Ac could transpose on the chromosome. Later, in 1948, she found that Ds and Ac could transpose on the chromosome. By changing the colouration of the kernels over each generation, by using controlled crosses, she concluded that Ac controls the transposition of Ds from chromosome 9 and when Ds is moved there is a breakage in the chromosome. By changing the colouration of the kernels over each generation, by using controlled crosses, she concluded that Ac controls the transposition of Ds from chromosome 9 and when Ds is moved there is a breakage in the chromosome.

Conclusion When Ds moves, the color gene is released which causes colour When Ds moves, the color gene is released which causes colour Mosaicism is caused by Ds transposing in random cells and not every cell. Mosaicism is caused by Ds transposing in random cells and not every cell. Size of the spot is determined by seed development Size of the spot is determined by seed development Transposition of Ds is determined by the number of Ac copies Transposition of Ds is determined by the number of Ac copies Ac controls the transposition of Ds from chromosome 9 and when Ds is moved there is a breakage in the chromosome. Ac controls the transposition of Ds from chromosome 9 and when Ds is moved there is a breakage in the chromosome.

Works Cited ga_08/McClintock_notes.pdf Accessed December - 20 – 11 ga_08/McClintock_notes.pdf Accessed December - 20 – 11 ga_08/McClintock_notes.pdf ga_08/McClintock_notes.pdf ck Accessed December - 20 – 11 ck Accessed December - 20 – 11 ck ck