Genes and Variation Chapter 17.1

Genetic Variation in a population increases the chance that some individuals will survive. Body size and feather patterns of penguins are examples of phenotypes or genotypes? A phenotype is a trait produced by one or more genes. Some penguins may be short and rounded or tall and slim.

Natural Selection Acts on different phenotypes in a population. A population must have genetic variation: Genetic diversity in a population or species as a result of new gene combinations (e.g. crossing over of chromosomes), genetic mutations, genetic drift, etc. The greater the variation in phenotypes, the more likely it is that some individuals can survive in a changing environment.

Examples If an unusually cold winter happens, short, rounded penguins might be able to stay warm more easily. But if there is a shortage of food, tall and slim penguins might be better divers allowing them to catch more fish.

Gene Pool Genetic variation is stored: in a population’s gene pool. Gene Pool: the combined alleles of all of the individuals in a population.

Allele Frequency A measure of how common a certain allele is in the population. First! Count the number of times an allele occurs in a gene pool. Then! Divide by the total number of alleles for that gene in the gene pool. Let’s try!

Gg GG GG gg

Allele Frequency g codes for green G codes for green How many g’s? 3 G codes for green How many G’s? 5 How many total alleles for skin color trait in gene pool? 8 Frequency of allele G? 5/8=0.625 Frequency of allele g? 3/8=0.375

Genetic Variation comes from several sources Mutation: is a random change in the DNA of a gene. Mutations in reproductive cells can be passed on to offspring. Increases the genetic variation in the gene pool.

Genetic Variation comes from several sources Recombination: new allele combinations form in offspring through a process. Most recombination occurs during MEIOSIS! When gametes are made, each parent’s alleles are arranged in new ways.