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Illustration of chromosome crossover during genetic recombination. In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet effect) is a process which, in the absence of recombination (especially in an asexual population), results in an accumulation of irreversible deleterious mutations.
This effect is mirrored in humans, where mutations in the WNT4 gene has been observed in MRKH syndrome patients, who display hyperandrogenism. Mutations in WNT4 gene are not always present in individuals with Müllerian anomalies or MRKH syndrome, but the WNT4 gene is the only gene that has been clearly implicated in MRKH.
Compartment boundaries establish these organizing centers [5] [7] by providing the source of morphogens [9] that are responsible for the positional information required for development and regeneration. [9] [10] The inability of cell competition to occur across the boundary, indicates that each compartment serves as an autonomous unit of growth.
Cellular compartments in cell biology comprise all of the closed parts within the cytosol of a eukaryotic cell, usually surrounded by a single or double lipid layer membrane. These compartments are often, but not always, defined as membrane-bound organelles. The formation of cellular compartments is called compartmentalization.
Many insects including hoverflies (C, D, E) and the wasp beetle (F) are Batesian mimics of stinging wasps (A, B), which are Müllerian mimics of each other.. In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species.
Fusion of late endosomes with lysosomes has been shown to result in the formation of a 'hybrid' compartment, with characteristics intermediate of the two source compartments. [8] For example, lysosomes are more dense than late endosomes, and the hybrids have an intermediate density. Lysosomes reform by recondensation to their normal, higher ...
Sertoli cells are specifically located in the convolutions of the seminiferous tubules, since this is the only place in the testes where spermatozoa are produced.
The female reproductive system is composed of two embryological segments: the urogenital sinus and the paramesonephric ducts. The two are conjoined at the sinus tubercle. [2] [3] Paramesonephric ducts are present on the embryo of both sexes.