* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 16-2 Evolution as Genetic Change
Pharmacogenomics wikipedia , lookup
Behavioural genetics wikipedia , lookup
Heritability of IQ wikipedia , lookup
Gene expression programming wikipedia , lookup
Designer baby wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Adaptive evolution in the human genome wikipedia , lookup
Dual inheritance theory wikipedia , lookup
Genetics and archaeogenetics of South Asia wikipedia , lookup
Genome (book) wikipedia , lookup
Group selection wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Koinophilia wikipedia , lookup
Human genetic variation wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Genetic drift wikipedia , lookup
Chapter 16: Evolution of Populations (16-2) Natural selection does not act directly on genes. In stead, it acts on phenotypes. Even though natural selection does not operate directly on genes, it can change the relative frequencies of alleles in a population over time. Evolution is any change in the relative frequencies of alleles in a population’s gene pool Natural selection on single-gene traits can lead to changes in allele frequencies and thus evolution See lizard story on page 397 (red v. black lizards) When traits are controlled by more than one gene, the effects of N.S. are more complex. N.S. can affect distributions of phenotypes in three ways. Chapter 16: Evolution of Populations (16-2) — occurs when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end… evolution causes an increase in the number of individuals with the trait at one end. — takes place when individuals near the center of a curve have higher fitness than individuals at either end…narrows the overall graph. —when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle… selection acts most strongly against individual of an intermediate type. Chapter 16: Evolution of Populations (16-2) In small populations, an allele can become more or less common simply by chance. Random change in alleles frequency is called genetic drift. A migration of a small group of a population is known as the founder affect. The Hardy-Weinberg principle states that allele frequencies in a population will remain constant unless one or more factors (5) cause those frequencies to change. Genetic Equilibrium—allele frequencies remain constant. Five conditions are required to maintain genetic equilibrium: Random Mating: all members of the population must have equal opportunity to produce offspring … In natural populations mating is rarely completely random. Large populations: genetic drift has less effect on large populations. Chapter 16: Evolution of Populations (16-2) No Movement Into or Out of the Population: the population’s gene pools must be kept together and kept separate from other populations. No Mutations: If genes mutate, new alleles may be introduced into the population, and allele frequencies will change. No Natural Selection: No phenotype can have a selective advantage over another. p is the frequency of the dominant allele q is the frequency of the recessive allele p2 = 2pq = q2 = TT Tt tt p+q=1 2 (1 means 100%) 2 p + 2pq + q = 1