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• Entry 57: Evolution Notes 2 What you will learn today… 1. How do we measure genetic variation in a population? 2. Why is genetic variation in a population important? 3. What are the sources of genetic variation in a population? What determines a heritable trait? DNA (gene) mRNA protein Observed trait Therefore, if traits vary in a population, then the genes (alleles) must vary in the population! A population with variation in traits… Grey White Tall ears Short ears ...is caused by variation in alleles Grey allele = G Tt GG TT Gg tt gg tt Gg tt GG tt Gg tt Gg White allele = g Tall ear allele = T Tt gg Short ear allele = t How do we measure genetic variation in a population? Grey allele = G 8 / 16 = 50% G Tt GG TT Gg tt gg tt Gg tt Gg tt GG tt Gg “Gene Pool” Tt gg White allele = g 8 / 16 = 50% g Tall ear allele = T 4 / 16 = 25% T Short ear allele = t 12 / 16 = 75% t How do we measure genetic variation in a population? Gene Pool- Total genetic information available in a population (all the alleles that are present). Allele Frequency- The percentage of an allele in the gene pool. Tells you whether a given allele is common or rare. Why is genetic variation in a population important? • A gene pool without much variation limits a species’ ability to further evolve. (Variation is one of the 4 factors required for natural selection to lead to evolution) • If populations do not adapt to their environment, they may become extinct. Sources of genetic variation 1) SEXUAL REPRODUCTION A. Meiosis – one allele is passed on from each parent (recall that sperm and eggs are haploid cells, each containing half the necessary genetic information). B. Random fertilization – only one of the millions of sperm involved in mating will fertilize the egg. The randomness of sexual reproduction explains why siblings can look so different. Sources of genetic variation 2) MUTATION Mutation means a change in DNA sequence. A new DNA sequence may = new allele of a gene. – Some mutations produce genes that are harmful (e.g. Huntington’s disease) – Most mutations produce genes that are neutral (neither helpful nor harmful) – Very, very few mutations produce genes that are advantageous The only way brand new alleles can be created is through mutation. Natural Selection • Individuals with advantageous genes are more likely to survive to reproduce and pass on these genes to their offspring. • Individuals without advantages genes are less likely to survive to reproduce, and these genes do not get passed on in the population. Conclusion • Mutation does NOT cause evolution – it is only a source of variation (just one of the factors required for natural selection) • Natural selection determines if the allele frequency will change within a population. • EVOLUTION= Change in allele frequency (A change in how often a form of a gene is present) Next Task: Kerosene Karl 1. Read the explanation on the back side of your Evolution Notes 2 sheet and answer the Prelab Questions. 2. In my Pickup Work folder open the Kerosene Karl activity. Follow the directions on your worksheet to complete the activity. 3. Whatever you don’t finish is HOMEWORK!!