<span>Alleles are two different forms of single gene that are located in specific position on a specific chromosome. It can be classified into two allele pairs: homozygous and heterozygous. In homozygous, both alleles are the same whether they are both dominant or recessive; while in heterozygous, one allele is dominant and the other is recessive.</span>
Answer:
The principal difference in development of Dorsoventral axis in deuterostomes and protostomes is something called inversion
Explanation:
In protostomates the neural tube is below the gut and the dorsal vessel is above the gut while in deuterostomates is the oppossite, there is an inversion and now, the neural tube is above the gut and the heart tube is below. In both cases the development is related to the gradient of expression of some genes, where the expresion of one gene supress the formation of one structure in one side of the axis.
In protostomates the TGT-B factor is expressed dorsally and supress neural tube formation and ventrally a sog gene is expressed and supress TGT-F factor allowing neural tube to develop. In deuterostomates, an homolog of TGT-B family gene BMP-4 is expressed ventrally while dorsally BMP inhibitors (sog gene like) are expressed.
Accordingly to some researchers, the first state of the common ancestor of deuterostomates and protostomates had an protostomate-like orientation in dorsoventral axis
A. the population of higher trophic levels is greater than lower trophic levels
Scientists have found that extracellular matrix component may induce specific gene expression in the embryonic tissues such as the liver and testes. For this to happen, there must be a direct communication between the extracellular matrix and the developing cells. The Integrins of transmembrane protein would most likely be involved in this kind of induction.
Integrins are the main principal receptors used by the cells of animal to bind to the matrix of extracellular. They are heterodimers and they function as transmembrane linkers between the actin cytoskeleton and the extracellular matrix. A cell can regulate the sticky activity of its integrins from within.
Learn more about integrins here
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