BIO 201 Lecture Notes - Lecture 26: Statistical Hypothesis Testing, Aflatoxin, Radiometric Dating
9 May 2016
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The amniote egg is impermeable to water, the embryo develops in a contained aqueous environment. Leathery or brittle shells retard water evaporation but allow gas exchange. Amniote eggs stores food in the form of yolk; embryos develop using energy from the yolk and hatch at an advanced stage. In several amniote groups, character state changes allow the embryo to develop inside its mother"s body. In (almost all) mammals the egg loses its shell entirely, while the functions of the extraembryonic membranes were retained and expanded. Broken genes-humans have the yolk genes but don"t make yolk because it"s an ancestral trait that has decayed via mutation (genotype and phenotype) Loss of coelom in flatworms; loss of bilateral symmetry in echinoderms; loss of egg shall and yolk in (most) mammals. On the phylogeny, parasitism is associated with the loss of functional genes (such as those require for synthesizing fats and cholesterol that are crucial for development.
