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Although neutral evolution remains the consensus theory among modern biologists, [3] and thus Kimura's resolution of Haldane's dilemma is widely regarded as correct, some biologists argue that adaptive evolution explains a large fraction of substitutions in protein coding sequence, [4] and they propose alternative solutions to Haldane's dilemma.
In humans, barring intersex conditions causing aneuploidy and other unusual states, it is the male that is heterogametic, with XY sex chromosomes.. Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J. B. S. Haldane, that states that if — in a species hybrid — only one sex is inviable or sterile, that sex is more ...
In 1957, Haldane articulated Haldane's dilemma, a limit on the speed of beneficial evolution, an idea that is still debated today. [8] He is also remembered for his work in human biology, having coined "clone", "cloning", and "ectogenesis". With his sister, Naomi Mitchison, Haldane was the first to demonstrate genetic linkage in mammals.
Heterosis or hybrid vigor, on the other hand, is the tendency of outbred strains to exceed both inbred parents in fitness. Selective breeding of plants and animals, including hybridization, began long before there was an understanding of underlying scientific principles.
Objections to evolution have been raised since evolutionary ideas came to prominence in the 19th century. When Charles Darwin published his 1859 book On the Origin of Species, his theory of evolution (the idea that species arose through descent with modification from a single common ancestor in a process driven by natural selection) initially met opposition from scientists with different ...
The work of Fisher, Haldane and Wright founded the discipline of population genetics. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked. [4] [5] John Maynard Smith was Haldane's pupil, whilst W. D. Hamilton was
It was produced by hybridisation experiments in the 1920s, when crosses were made between yak bulls and both pure bison cows and bison–cattle hybrid cows. [1] As with many other inter-specific crosses, only female hybrids were found to be fertile (Haldane's rule). Few of the hybrids survived, and the experiments were discontinued in 1928. [2]
Haldane's sieve is particularly relevant in situations where the effects of natural selection are strong and the beneficial mutations have a significant impact on an organism's fitness. According to Haldane's sieve, when a new advantageous mutation arises in a population, it initially occurs as a single copy (a de novo mutation ), borne by an ...