Evolution and Populations –Essential Questions p. 431-435 How can a lethal gene exist in a gene pool and not disappear? What is genetic drift? Explain each of the three different types of genetic drift. According to the Hardy-Weinberg Principle, what five things must occur to prevent genetic drift? 5. When do mutations pass from one generation to the next?

Population Genetics

Alleles that are lethal in a homozygous individual may be carried in a heterozygote and thus maintained in a gene pool. Know the conditions for Hardy-Weinberg equilibrium in a population and why these conditions are not likely to appear in nature. Know how to solve the Hardy-Weinberg equation to predict the frequency of genotypes in a population, given the frequency of phenotypes.

– genes have at least two alleles Genetic Variation – genes have at least two alleles   Gene Pool – all genes, including all of the different alleles, present in a population

Relative Frequency – the number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur -  evolution is any change in the relative frequency of alleles in a population

Genetic Drift Stabilizing selection Disruptive Selection Directional Selection

Lethal genes remain in a gene pool at low frequency if they are recessive. They are carried by hybrids (heterozygous individuals).

Sources of Genetic Variation Mutations – changes in a DNA sequence - additions, deletions, substitutions of nucleotides, and rearrangement of chromosomes neutral, harmful, or beneficial to be passed on they must be in sex cells

Hardy-Weinberg Principle Genetic Equilibrium – allele frequencies remain constant as long as there remains: 1.  random mating 2.  a very large population 3. no movement into or out of the population 4.  no mutations 5. no natural selection *** NOT likely to happen in nature

p2 + 2pq + q2 =1 p + q = 1 2pq = % of Aa q2 = % of aa p2 = % of AA 2pq = % of Aa q2 = % of aa q = # of a alleles p = # of A alleles

Use the chart to determine the frequency of the AA genotype Use the chart to determine the frequency of the AA genotype. What is the frequency of the A allele? Flowers(population 100) AA Aa aa 36 48 16