Textbook Notes (368,629)
Canada (162,027)
Biology (1,177)
Biology 1225 (113)
Chapter 12

chapter 12 bio 1225 notes.docx

9 Pages
Unlock Document

Biology 1225
Michael Butler

Chapter 12 Processof Evolution - Biological Evolution is genetic change in a line of descent (lineages) through successive generations. - Members of a population generally have the same number and kinds of genes, which give rise to the same assortment of traits. - Each gene may exist in two or more slightly different forms (alleles) - Different individuals don’t necessarily inherit the same alleles so they may differ in the details of their traits. - Natural selection is simply the result of a difference in survival and reproduction among individuals who differ in one or more traits - A species consists of one or more populations of individuals that can interbreed under natural conditions and produce fertile offspring, and that are reproductively isolated from other such populations. There are two types of reproductive isolation mechanism, pre-mating and post- mating. - Pre-mating reproductive isolating mechanisms act to prevent mating, these include temporal isolation, ecological isolation, behavioural isolation and mechanical isolation - Post-mating reproductive isolation mechanisms act after mating has occurred, this includes gamete mortality, and post zygote mechanisms (as is found with the product of the union of a female horse and a male donkey, the mule that results is sterile) - New Species evolve from variant individuals of existing species. Therefore, all species that have ever lived on Earth are related - However, it is estimated that nearly 99.9% of all species that have existed since the beginning of life on the Earth are no longer alive. - Most scientists have concluded that extinction is the ultimate fate of most, if not all, species. *****Be sure to understand what causes evolution? Have a clear understanding of natural selection and how it operates. You should know the kinds of anatomical, biochemical and genetic evidence in support of evolution. You should be able to distinguish between the different kinds of reproductive isolating mechanisms Section 12.7 in NOT on exam. 1 12.2 Making Waves in the Gene Pool page 213 population – a group of organisms of the same species that live in a specific location and breed with one another more often than they breed with members of other populations allele frequency – abundance of a particular allele among members of a population gene pool – all the alleles of all the genes in a population; a pool of genetic resources lethal mutation – mutation that alters phenotype so drastically that it causes death microevolution – change in an allele’s frequency in a population or species genetic equilibrium – allele frequencies of a population do not change ie. The populating is not evolving. Genetic equilibrium can occur if everyone of the following five conditions are met: a. mutations never occur b. the population is infinitely large c. the population is isolated from all other populations of the species d. mating is random e. all individuals survive and produce the same number of offspring *** All five conditions can never be met in nature so natural populations are never in equilibrium*** 1. The individuals of a population share physical, behavioural and physiological traits 2. Alleles which arise by mutation are the basis of differences in the forms of shared traits. 1. All alleles of all genes in a population form a pool of genetic resources called a gene pool 2. Mutation may be lethal, neutral or adaptive 3. Microevolution or changes in allele frequency within a population’s gene pool occurs consistently in natural populations by process of mutation, natural selection and genetic drift. 4. We use deviations from a theoretical genetic equilibrium to study how populations evolve 2 Take home message What is microevolution? 1. Individuals of a natural population share morphological, physiological and behavioural traits characteristic of the species. Alleles are the basis of differences in the details of those shared traits. 2. All alleles of an individuals in a population make up the population’s gene pool . An allele’s abundance in the gene pool is called the allele frequency 3. Microevolution is change in allele frequency. It is always occurring in natural populations because processes that drive it are always operating. ***Microevolution is always occurring in natural populations because processes that drive it – mutation, natural selection and genetic drift- are always operating. Even though we recognize evolution none of it is purposeful. Sources of Variation in Traits Among individuals of a species: table 12.1 pg213 Mutation- source of new alleles Crossing over at - introduces new combinations of alleles into chromosomes Meiosis 1 Independent- mixes maternal and paternal chromosomes Assortment At Meiosis 1 Fertilization- combines alleles from 2 parents Changes in- often dramatic changes in structure and function Chromosome Number or structure 3 12.3 Modes of Natural Selection page 215 directional selection –mode of natural selection in which a phenotype at one end of a range of variation is favoured stabilizing selection – mode of natural selection in which an intermediate form of a trait is favoured over extreme forms disruptive selection – mode of natural selection that favours forms of a trait at the extremes of a range of variation; intermediate forms are selected against 1. Natural selection, the process in which environmental pressures result in the differential survival and reproduction of individuals of a population, occurs in patterns. 2. With directional selection, a phenotype at one end of a range of variation is favoured. 3. Stabilizing selection acts on extreme forms of a trait, so intermediate forms are favoured 4. With disruptive selection, intermediate forms of a trait are selected against, and forms at the extremes are favoured. Take Home Message How does natural selection drive Evolution? 1. Natural selection occurs in different patterns depending on the species involved and the pressures in their particular environment 2. With directional selection, a phenotype at one end of a range of variation is favoured ***Example: populations of rock pocket mice: mice with dark fur are more common in dark areas and mice with light fur are more common in light areas because mice with coat colors that do not match their surroundings are more easily seen by predators so they are preferentially eliminated from the populations. Pg 216 3. With Stabilizing selection, an intermediate phenotype is favoured and extreme forms are selected against ***Example: pg. 217 Social Wavers with an intermediate body mass of 29gr are more likely to survive breeding season 4. With disruptive selection an
More Less

Related notes for Biology 1225

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.