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Pointed out the interrelationships between cytology and Mendelism, closing the gap between cell morphology and heredity.
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Nettie Stevens Edmund Wilson and Independently described the behavior of sex chromosomes-XX determines female; XY determines male.
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First experiments on quantitative traits in broad beans by Wilhelm Johanssen and in wheat by Herman Nilsson-Ehle.
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In DNA, there are equal amounts of A and T, and equal amounts of C and G, as shown by Erwin Chargaff. However, the A+T to C+G ratio can differ between organisms.
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DNA is the molecule that mediates heredity, as shown in bacteriophage labeling experiments by Alfred Hershey and Martha Chase.
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DNA is in the shape of a double helix with antiparallel nucleotide chains and specific base pairing. This was deduced by Watson and Crick, who used Rosalind Franklin's data provided by Maurice Wilkins.
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DNA replication is semi-conservative, as shown by Meselson and Stahl using equilibrium density gradient centrifugation.
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The first restriction enzyme is purified by Hamilton Smith.
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The first cloning of a mammal (Dolly the sheep) is performed by Ian Wilmut and colleagues, from the Roslin institute in Scotland.
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Controversies continue over human and animal cloning, research on stem cells, and genetic modification of crops.
