BIO120H1 Lecture 19: Lecture 19.docx

• School: UTSG
• Department: Biology
• Course: BIO120H1
• Professor: James Thomson

Document Summary

Missing pollinator of flower with large floral tube. One goes extinct, so does other frequency of phenotype in variation usually reaches a middle point. Selection done not by humans but by biotic and abiotic forces. Mechanism of selection stabilizing(average selected for, no change in mean trait value), directional(shifted over) , disruptive (favors both extremes, 2 parabola, not one). Large and small offspring die, stabilizing slection on mean. Peter and rosemary grant, directional selection on beak size, favored birds with large beak. Great tits decrease in laying date with increase of temperature provides adaptive plasticity(change of phenotype), no type of selection. Different birds with two types of beaks specialize on soft seeds and hard seeds. Its hard to nail down agent of selection. Humans effect of increasing evolution in the wild industrial melanism and evolution of heavy metal tolerant grasses in britian there were two forms, light and black. Few black, caused by one single dominant allele.