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Jan 31

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BIO201 Jan 31 st Natural Selection in the Lab - animals have enzymes to metabolize alcohol Natural Selection Since Darwin – The Modern Synthesis - the union of genetics and evolution is called the ‘modern synthesis’ o knowledge of genetics facilitates understanding of the mechanisms of evolution o alleles (alternate forms of a gene) are the basis of variation of traits o mutations (changes in DNA) can create new alleles and provide the basis for new traits o natural selection provides a filter that selects for/or against new traits Natural Selection Since Darwin - natural selection does not result in perfection - natural selection causes organisms to become better fit to their environment o organisms are not necessarily better, just ‘better fit’ to a particular situation - adaptation that is beneficial in one situation might not be beneficial in another - selection acts on variations that already exists - adaptations involve trade-offs Adaptations are constrained - * selection acts on variations that already exist - ex. panda’s thumb – grown from wrist bones o not as efficient as the opposable thumb - ex. upright posture for humans o bipedal walking o back and knee injuries? Patterns of Selection - different environmental conditions can lead to changes in populations o one direction/directional pattern o ex. polar and grizzly bears  direction to be large  favours a single extreme phenotype • hibernation, territorial/mating advantage, etc. o stabilization selection  selecting for the intermediate/average  ex. height in humans – follows the normal curve  ex. bird’s eggs – acts to eliminate both extreme phenotypes • favours intermediate variants  ex. infant mortality related to birth weight • low/high birth weight – high mortality rate • in humans, infants with intermediate weight at birth have the highest survival rate Diversifying Selection - bimodal distribution - large and small bill sizes favoured over intermediate size - relatively rare - large beaks can break the large seeds, small beaks can break small seeds, but intermediate beaks have a hard time breaking the small and large seeds – reproduce less - favours both extreme Competition - for resources of limited supply Predation - one organism consuming another - effect on natural selection/survival/reproduction: o ex. lions will kill off all slow gazelles – lions are developing for fast gazelles – gazelles are developing for fast lions – influencing each other o predator always trying to catch up to prey, prey always trying to escape predator Symbiosis - two different species live in very close proximities within one another – very close relationship - co-evolution: pattern of evolution in which two interacting species reciprocally influence each other’s adaptations in some way o ex. pollination, parasite and host - if one species is eliminated, the other may eliminate as well – ex. orchid and moth What is meant by success with regard to the organisms that live on this planet? - adaptation o survival and reproduction o organisms today have inherited the best combination of traits from successful ancestors that enables them to successfully survive and reproduce Natural Selection – Lecture 7 1. mirco-evolutionary forces 2. non-random mating and sexual selection 3. natural selection and skin colour in humans 4. natural selection and defensive colouration 5. national selection overview Microevolution: Evolutionary Forces - five evolutionary forces can significantly alter the genetic structure of a population o 1. mutation  errors in DNA replication – simply means change (not negative)  source of new variation  relatively rare  may be harmful, neutral, or advantageous  beneficial mutations can increase frequency fairly quickly  ex. bacteria • short generation time • important source of variation o 2. gene flow  flow/exchange/passing on of genetic information  migration: movement of individuals from one population to another, followed by breeding
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