Diversity and Evolution SC.912.L.151 SC.912.L.15.10 SC.912.N.1.3 SC.912.N.2.1 SC.912.L.15.8

Survival of the Sneakiest Roles: Boy/narrator (B) Girl (G) Sound effect person (SE) Male cricket 1 STRONG, ATTRACTIVE, SINGING (MC1) Female cricket (FC) Male Cricket 2 SNEAKY (MC2) Bat (BAT) Male cricket 3 (MC3) Minor cricket 4 (MC4) Minor cricket 5 (MC5)

4 Main Principles of Natural Selection Variation exists within a population Organisms compete for limited resources Organisms produce more offspring than can actually survive Individuals with variations suitable for their habitat are the ones that SURVIVE and REPRODUCE

Sources of Variation -Natural selection requires variation…this is where it comes from: Mutations Alleles can be randomly created Only source of variation not involving rearranging alleles Sexual reproduction (genetic recombination) Crossing over (prophase 1) Independent assortment of homologues (metaphase 1) Random joining of gametes during fertilization Diploidy Having two copies of each chromosome therefore having two alleles for every phenotype Heterozygous genotypes allow recessive allele to be stored secretly in gene pool Outbreeding Mating with unrelated partners  increases probability of making different combos of alleles Balanced polymorphism Maintaining different phenotypes in the population This does NOT involve recombining alleles All these involve recombination of alleles

Genetic variation comes from several sources. Can you think of some? Mutation is a random change in the DNA of a gene. can form new allele How can mutations be passed on to offspring? Recombination forms new combinations of alleles. usually occurs during meiosis, What is the process called? CROSSING OVER parents’ alleles arranged in new ways in gametes

Sexual Reproduction Two parent cells join to form new individual Parent cells are called GAMETES Gamete cells different than other body cells b/c they only have HALF the total number of chromosomes Male gamete sperm cell (human gamete= 23 chromosomes) Female gamete egg cell (human gamete= 23 chromosomes) During sexual reproduction, new cell recieves 23 chrm. From mom and 23 chrm. From dad for a total of 46 chrm. (a complete human set) Offspring= 46 chromosomes The genes are not inherited in the same exact pattern, therefore the offspring is slightly different from parents Offspring from sexual reproduction are GENETICALLY DIFFERENT from parents

Recombination during Gamete Formation Gametes form during a process called meiosis (more on this later) During meiosis, chromosomes that are similar in size, shape and genetic material pair up with each other (homologous chromosomes) These paired up chromosomes swap parts in process called “crossing-over” Process in which chromosome segments are broken off and exchanged Crossing Over INCREASES the # of possible genetic combinations in the offspring

Germ Mutation Mutation in a gamete CAN BE passed off to offspring and AFFECT survival of those offspring and their descendants Helpful mutations persist (stay around) in population Helpful mutations contribute to evolution and speciation

5 Types of Natural Selection Directional selection Disruptive selection Stabilizing selection Sexual Selection Artificial selection (form of directional selection; not natural)

1. Directional selection Favors traits at one EXTREME of the range of possible traits Result: traits at the opposite end disappear If this continues for many generations, favored traits become more and more extreme Result: distinct changes in allele frequencies of the population Examples: Insecticide resistance Peppered moth

2. Disruptive Selection Environment favors more EXTREME or UNUSUAL traits over common traits Extreme or unusual traits at both ends of the spectrum are favored…common traits disappear over time Leads to BALANCED POLYMORPHISM Population divided into two phenotypes

3. Stabilizing Selection Favors the more common traits in a population as opposed to the more EXTREME or unusual traits Eliminates individuals that have EXTREME or unusual traits Maintains the existing population frequencies of common traits while selecting against all other trait variations Example: Infant birth weight

4. Sexual Selection Females Males Differential mating of males (sometimes females) in a population Mating behavior in a population that produces more NUMEROUS and/or more FIT offspring Females greater energy investment in producing offspring than males increase fitness by increasing QUALITY of offspring by selecting SUPERIOR males to mate with Males contribute little energy to the production of offspring Males increase fitness by maximizing the QUNATITY of offspring produced

4. Sexual Selection (continued) Two types of Sexual Selection Male competition Males compete with other males for mating opportunities Males compete with other males to produce greater quantities of offspring Leads to contests of strength that award mating opportunities to the strongest male Female choice Leads to traits or behaviors in males that attractive to females Females tend to strengthen the gene pool by choosing superior males to mate with Females respond to behaviors or traits (dances, songs, colors) that attract them to certain males

5. Artificial Selection Type of DIRECTIONAL selection Carried out by humans Sowing seeds Cauliflower, Brussels sprouts, broccoli, kale bred from one species of wild mustard Breeding animals Dogs Race horses Not NATURAL selection

Mechanisms for Evolution VARIATION is important OTHER than 1. Natural Selection: VARIATION is important in all of these! Modern genetics has shown us that there are other ways to change the allele frequencies in a population besides natural selection…. Genetic Drift Gene Flow Non-Random Mating Mutation

Overview Natural Selection Genetic Drift Gene Flow Non-random mating Increase or decrease in allele frequencies due to impact of ENVIRONMENT Genetic Drift RANDOM increase or decrease in allele frequencies in a population Gene Flow Introduction or removal of alleles from population when individuals leave (emigrate) or enter (immigrate) Non-random mating When individuals choose mates based on particular traits When individuals only choose nearby individuals to mate with Mutations Introduce NEW alleles that may provide a selective advantage MOST mutations are deleterious (HARMFUL)

2. Genetic Drift changes in the allele frequency within a population that occur by chance genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals No guarantee that the new population will be better suited to its environment than the original population Effect of Genetic drift is very strong and dramatically influences evolution of small populations (fewer than 100) Before After The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals. That, in a nutshell, is genetic drift.

2. Genetic Drift Two types of Genetic Drift Founder Effect When allele frequency of group of migrating individuals, by CHANCE, are different from their original population Bottleneck Effect Occurs when a population undergoes a dramatic decease in size Regardless of cause of bottleneck (natural disaster, predation, disease), small population is now very vulnerable to genetic drift Certain alleles have greater effect on population than other alleles The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals. That, in a nutshell, is genetic drift.

migration of alleles INTO or OUT of a population 3. Gene Flow migration of alleles INTO or OUT of a population Usually INCREASE population’s genetic diversity Biggest Factor that Effects Gene Flow: MOBILITY For example: The immigration and emigration of organisms. The dispersal of seeds or spores.

2 Major Forms of Non-Random Mating Choice of mate based on preference Example: Similarity to one’s own traits Differences from one’s own traits Geographical proximity to mate 2 Major Forms of Non-Random Mating Inbreeding When individuals mate with relatives Sexual Selection Females choose male mate based upon: Attractiveness Behavior Ability to defeat other males in contests

5. Mutations CAUSES: Spontaneous Natural factors Ultraviolet radiation from the sun Exposure to chemicals Exposure to radiation Introduces new alleles into a gene pool that NEVER existed before VITAL b/c provides source for new variation What is a mutation: Change to an organisms genetic material (DNA) Change the NUCLEIC ACIDS that make up one or more genes Changes can produce new traits that can either HELP or HURT the survival of an organism BENEFICIAL Mutations help organism NEUTRAL Mutations have no effect on organism NEGATIVE Mutations hurt organisms chances for survival

Allele frequencies measure genetic variation. how common allele is in population can be calculated for each allele in gene pool Calculate the allele frequency for G(Green frogs) in the population Calculate the allele frequency for g (brown frogs) in the population

How to calculate the ALLELE Frequency in a Gene Pool Allele X or Allele x for certain TRAIT Allele frequency X = # of allele X in population (gene pool) total # of alleles (X + x) in population (gene pool)