* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 23
Survey
Document related concepts
Designer baby wikipedia , lookup
Genome evolution wikipedia , lookup
SNP genotyping wikipedia , lookup
Pharmacogenomics wikipedia , lookup
History of genetic engineering wikipedia , lookup
Behavioural genetics wikipedia , lookup
Frameshift mutation wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Heritability of IQ wikipedia , lookup
Genetics and archaeogenetics of South Asia wikipedia , lookup
Point mutation wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Koinophilia wikipedia , lookup
Human genetic variation wikipedia , lookup
Population genetics wikipedia , lookup
Genetic drift wikipedia , lookup
Transcript
Chapter 23 Hardy-Weinberg Microevolution Change in a population's alleles over a period of time. It is very difficult to detect changes that occur on the microscopic level. These changes must manifest themselves in the organisms phenotype. Since individuals do not evolve, one must keep a close eye on the individuals population to detect any change in genotypic modification. Biologists have a way to help them detect such changes; called the Hardy Weinberg theorem. 1000 total alleles (aa) (AA) (Aa) Can these conditions really exist? NO!!! Other method Large ear allele (L) has a .8 frequency Small ear (l) allele has a .2 frequency The percent of each of the three phenotypes in a given population. p2 = .64 2pq = .32 q2 = .04 = 1 64% 32% 4% = 100% If we know the percent of the homozygous recessive organisms, we can take the square root of the decimal value and determine the frequency. Determine the frequency of the dominant allele by subtracting it from 1. Sample Problem #1 In Drosophila (fruit fly), the allele for normal wing length is dominant over the allele for short wings. In a population of 1000 individuals, 360 show the recessive phenotype. How many individuals would you expect to be homozygous dominant for the trait? Sample Problem #2 The allele for a widow's peak (hairline) is dominant over the allele for a straight hairline. In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous for the trait? Sample Problem #3 The allele for a hitchhiker's thumb is dominant over a straight thumb. In a population of 1000 individuals, 510 show the dominant phenotype. How many individuals would you expect for each of the three possible genotypes for this trait. Microevolution Genetic Variation The substrate for natural selection Variations within populations Polymorphism-two or more forms of a characteristic in a population that are readily noticeable (red and white flowers) Gene diversity-Measuring the # of heterozygous alleles in the entire genome Nucleotide diversity- comparing nucleotide sequences from DNA samples Variations between populations Geographic variation- results from differences in genetic structure either between populations that inhabit different areas. Variation along a geographic axis is called a cline. Average size of yarrow plants (Anchillea), gradually decreases with increasing variation. Fig. 23.8 In contrast to clines, isolated populations typically demonstrate discrete differences. For example, populations of house mice were first introduced to the island of Madiera in the 15th century, but isolated populations developed that were separated by mountains. Some isolated populations have evolved differences in karyotypes probably through genetic drift. Fig. 23.9 What is the source of variation? Mutation Mutation - changes in the nucleotide sequence of DNA. Mutations of individual genes are rare and random. Mutations in somatic cells are lost when the individual dies. Mutations in gametes can be passed to offspring. Sexual recombination Random segregation of homologous chromosomes and random union of gametes creates Sexual reproduction recombines old alleles into fresh assortments every generation. How is variation preserved?