1. In the late 180os, a biologist study- ing animal embryos coined the phrase \"

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1. In the late 180os, a biologist study- ing animal embryos coined the phrase "ontogeny recapitulates phylogeny," meaning that the physical develop- ment of an animal embryo (ontogeny) seemed to retrace the changing form of the species during its evolutionary history (phylogeny). Why would em- bryonic development retrace evolu- tionary steps? 2. The photos shown below illustrate a case of synpolydactyly. This genetic abnormality is characterized by web- bing between partially or completely duplicated fingers or toes. The same mutations that give rise to the human phenotype also give rise to a similar phenotype in mice. In which family of genes do you think these mutations occur? Courtesy of Dr. Sajid Malik, from www.biomedcentral.com/1471-2350/8/78 Less than a minute 0 pages left

Explanation / Answer

An organism's current evolutionary status is recapitulated in its embryonic development. The embryo of humans displays tail which represents its evolutionary origin from its ape like ancestors. During the course of evolution, particular set of genes are selected over others in each group leading to specialization. The presence of these primitive characters is an ancestral trait governed primitive genes expressed by most of the organisms belonging to a same group. The development or the maintainace of that ancestral trait is affected differentially by newly evolved genes in different groups. In apes, tail provides selective advantage. So, they maintained the ancestral trait. For humans, tail does not provide advatage. So, new genes in humans have made sure that unnecessary organs are not produced at the mature stage.

Genes involved in separation of organs are mutated in the given case of Synpolydactyly.

Synpolydactyly in humans is caused by mutations in homeobox d13 (HOXD13) gene.

It is a homeobox transcription factor that plays a major role in morphogenesis of all multicellular organisms.

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1. In the late 180os, a biologist study- ing animal embryos coined the phrase \"

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