Presentation is loading. Please wait.

Presentation is loading. Please wait.


Similar presentations

Presentation on theme: "EVOLUTION: PROCESSES & PATTERNS"— Presentation transcript:


2 BIOLOGY EOC BENCHMARK SC.912.L Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

3 VIDEO: Simpson Evolution
Why is Homer evolving?

4 Convergent Evolution different organisms that live in similar environments become more alike in appearance and behavior. environment selects similar adaptations in unrelated species. Organisms develop analogous structures (same function, but different origins)

5 Coevolution two species evolve together.
There is a mutual evolutionary influence between two species. The species have a symbiotic relationship (interaction between members of two populations). Example: - Birds and flowers

6 Divergent Evolution ancestral species gives rise to a number of new species that are adapted to different environmental conditions and are less alike. Often occurs when a species colonizes a new environment. Also known as adaptive radiation.

THERE ARE FOUR MECHANISMS THAT CAN GIVE RISE TO EVOLUTION: MUTATION GENETIC DRIFT MIGRATION (Gene Flow) 4.NATURAL SELECTION Greatly and quickly seen in isolated populations like those on islands. - Allele frequency will change over generations; situations/ENV will favor one allele over another - Those populations at equilibrium are not evolving - Species with more genetic diversity will adapt better to environmental changes

In nature, White Bengal tigers arises from the mating of two Bengal tigers with recessive genes for the white color of fur. The gene is recessive has the effect that offspring (cubs / kittens) only become white if they inherit the recessive gene from both parents. It is the same principle as with brown and blue eyes. The inbreeding producing all these White tigers is neither good nor healthy for the tigers. In nature White tigers have, at least theoretically as there probably arent any, a less chance of surviving than normal colored tigers due to their lack of camouflage compared to the normal Yellow Tigers. Below is a very simplified illustration (Fig 1) of how the transfer of genes coding for fur color works. Consider to yellow Bengal Tigers mating. If they are both carriers of the recessive gene there's a 25 percent chance that their cubs will be white. If a white and a yellow Bengal tiger mates there's a 50 percent chance that the offspring will be white. The chances of getting more White tigers can be enhanced by letting tigers that are related mate. This is however the definition of inbreeding.

TIGER POPULATION Allele frequencies: Proportion of orange fur-pigment alleles in the population Proportion of white fur-pigment alleles in the population Evolution is a change in the allele frequencies of a population over time. For example, a change in the proportion of pigment alleles in the population of tigers means that evolution has occurred.

10  MUTATION #1 A mutation can create
a new allele in an individual. When this happens, the population experiences a change in its allele frequencies and, consequently, experiences evolution. #1 EVOLUTIONARY CHANGE: MUTATION MECHANISMS OF EVOLUTION Mutagen DNA Normal base- pair sequence Mutated base- pair sequence Normal protein Mutated protein Despite mutation’s vital role in the generation of variation, mutations almost always cause early death or lower the reproductive success of an organism. Normal phenotype Mutated phenotype

11 Mutations Are rare because you have self correcting enzymes
Natural Process that produces genetic diversity Not all mutations are bad Some won’t affect the body at all Blood types/ear lobes Some are advantageous (thumb) Brain Pop: Genetic Mutations

12 COMPUTER ACTIVITY: Sex and the Single Guppy
The purpose of this activity is to analyze how guppy populations change over time. The simulation activity allows you to start with a pool of guppies and your choice of predators, you will be able to watch what happens to your guppy population and how the introduction of predators can affect the guppy's appearance. The simulation will help you understand what pressures drive guppy evolution.

population can experience random changes in allele frequency that do not influence reproductive success which leads to evolution POPULATION BEFORE GENETIC DRIFT Allele frequencies: cleft chin (dominant) smooth chin (recessive) Neither allele is related to reproductive success. Inheritance is based solely on chance. REPRODUCTION In this example, a heterozygous couple (Cc) could have two children that are homozygous recessive (cc), causing an increase in the proportion of recessive alleles in the population. POPULATION AFTER GENETIC DRIFT There are now more recessive alleles in the population than before. FIXATION Genetic drift leads to fixation when an allele’s frequency becomes 100% in a population. If this occurs, there is no longer genetic variation for the gene.

The founding members of a new population can have different allele frequencies than the original source population and, consequently, the new population experiences evolution. SOURCE POPULATION Allele frequencies: 5 digits per hand (recessive) >5 digits per hand (dominant) A group of individuals may leave a population and become the founding members of a new, isolated population. AMISH NEWLY FOUNDED POPULATION The new population will be dominated by the genetic features present in the founding members.

15 ARTICLE: The Amish and Founder Effect

Occasionally, famine or disease or rapid environmental change may cause the deaths of a large, random proportion of the individuals in a population. SOME CATASTROPHE SOURCE POPULATION EXTREME AND RAPID ENVIRONMENTAL CHANGE NEW POPULATION The new population will be dominated by the genetic features present in the surviving members. All cheetahs living today can trace their ancestry back to a dozen or so individuals that happened to survive a population bottleneck about 10,000 years ago! Unless more individuals are introduced to the population, mating options will be limited thus decreasing variation in the gene pool (decreasing genetic diversity).

17 LAB: Genetic Drift Activity

18 #3 MECHANISMS OF EVOLUTION MIGRATION After a group of individuals migrates from one population to another, both populations can experience a change in their allele frequencies and, consequently, experience evolution. MIGRATION (GENE FLOW) 1 BEFORE MIGRATION Two populations of the same species exist in separate locations. In this example, they are separated by a mountain range. Population 1 Population 2

19 #3 MECHANISMS OF EVOLUTION MIGRATION After a group of individuals migrates from one population to another, both populations can experience a change in their allele frequencies and, consequently, experience evolution. MIGRATION (GENE FLOW) 2 MIGRATION A group of individuals from Population 1 migrates over the mountain range. Population 1 Population 2

20 #3 MECHANISMS OF EVOLUTION MIGRATION After a group of individuals migrates from one population to another, both populations can experience a change in their allele frequencies and, consequently, experience evolution. MIGRATION (GENE FLOW) 3 AFTER MIGRATION The migrating individuals are able to survive and reproduce in the new population and they may experience evolutionary changes from population 1. Population 1 Population 2

21 #4 3 Conditions that must occur for Natural Selection Mechanism of
Evolution Natural Selection #4 1. VARIATION OF A TRAIT IN A POPULATION The tiniest dog in a litter has reduced differential reproductive success. Its more robust siblings prevent access to the food it needs to grow and thrive. 2. The trait must be inheritable 3. One version of the trait must be in greater abundance than a different version of the trait.

22 Natural Selection There is indirect and direct evidence of
I. Indirect – we find it, not witness it II. Direct – we are witness to the development of Will be seen when there is: Over population Inheritance variation Struggle for survival (abiotic factors too) Evidence: Fossils Embryos Comparative Anatomy 5. Biogeography Adaptation Field/lab Experiments

23 ? How long can a fruit fly survive without food?

The average fruit fly can survive about 20 hours without food. Number of flies GENETICALLY ‘UNFIT’” FLY A MORE GENETICALLY ‘FIT’ FLY Hours until starvation

25 THE EXPERIMENT 1 INITIAL SETUP Start with a cage that contains a large number of fruit flies (5,000), and remove the food. = 500 fruit flies 2 TESTING STARVATION RESISTANCE Wait until 80% of the flies starve to death, then return the food to the cage. Record the average starvation-resistance time. Food removed Food returned Eggs Only the most starvation-resistant flies live to lay eggs. New generation Can fruit flies evolve so that they can resist starvation longer? Can we see Natural Selection at work? (YES) ? 3 START NEW GENERATION After the surviving flies eat a bit, collect the eggs those flies lay and transfer them to a new cage.

26  THE RESULTS GENERATION 1 Average starvation resistance: 20 HR.
Number of flies Hours until starvation GENERATION 2 Average starvation resistance: 23 HR. Number of flies Hours until starvation Experiment continues through 60 generations. GENERATION 60 Average starvation resistance: 160 HR.---this is evolution (change) at work Number of flies Over many generations of natural selection, the population changes! The flies now resist starvation much longer. Hours until starvation

27 Natural Selection Individuals with favorable traits are more likely to leave more offspring better suited for their environment Example: English peppered moth (Biston betularia) Peppered Moth Lab

28 Peppered Moth Natural Selection Simulation

29 Peppered Moth Natural Selection Simulation


Evidence of NS: Adaption The honeycreepers of Hawaii have adapted to a wide range of habitats, yet still closely resemble a finch-like shared ancestor found nearly 2,000 miles away---the major difference is the bill . BIOGEOGRAPHY: HAWAIIAN HONEYCREEPERS Mainland finch (probable shared ancestor) ’Akeke’e honeycreeper Maui Parrotbill honeycreeper ’I’iwi honeycreeper BIOGEOGRAPHY: HONEYCREEPERS--- A MODERN DAY DARWIN’S FINCH SCENARIO

32  Evidence of NS: biogeography Sugar glider Numbat Tasmanian wolf
BIOGEOGRAPHY: AUSTRALIAN MARSUPIALS AND THEIR PLACENTAL COUNTERPARTS AUSTRALIAN MARSUPIALS Sugar glider Numbat Tasmanian wolf PLACENTAL COUNTERPARTS Gray squirrel Giant anteater Gray wolf Though less related to each other than you are to a shrew, these marsupials and their placental counterparts (both mammals) have come to resemble each other as natural selection has adapted them to similar habitats.

1 VARIATION FOR A TRAIT Different traits are present in individuals of the same species 2 HERITABILITY Traits are passed on from parents to their children. 3 DIFFERENTIAL REPRODUCTIVE SUCCESS In a population, individuals with traits most suited to reproduction in their environment generally leave more offspring than individuals with other traits. MECHANISMS OF EVOLUTION NATURAL SELECTION When these three conditions are satisfied, the population’s allele frequencies change and, consequently, evolution by natural selection occurs.

34 Running speed in rabbits can vary from one individual to the next.
NATURAL SELECTION IN NATURE Running speed in rabbits can vary from one individual to the next. 1 VARIATION FOR A TRAIT Speed The trait of running speed is passed on from parents to their offspring. 2 HERITABILITY In a population, rabbits with slower running speeds are eaten by the fox and their traits are not passed on to the next generation. 3 DIFFERENTIAL REPRODUCTIVE SUCCESS

When first used as medicine in the 1940s, penicillin was uniformly effective in killing the bacterium Staphylococcus aureus. Today, natural selection has led to an increase in antibiotic-resistant alleles, and humans are increasingly at risk from untreatable Staphylococcus infections.(this is ongoing evolution taking place right now ) Most of the Staphylococcus is killed. Staphylococcus Very little of the Staphylococcus is killed. Penicillin Kill zone 1940s Today

36 A single species of grass is planted on a golf course
A single species of grass is planted on a golf course. On the putting greens, it is cut very frequently / on the fairways it is cut only occasionally / in the rough it is almost never cut at all. EVOLUTION IN PROGRESS: GREEN GRASS ON A GOLF COURSE Over the course of only a few years, grass plants from the same stock had developed into three distinct populations as a result of the frequency at which they were cut. Rough Fairway Putting green SELECTIVE PRESSURE Monthly mowing schedule LIFE IS SHORT SO MUST REPRODUCE RAPIDLY WITH LARGE SEED PRODUCTION SEXUAL MATURATION SLOWEST SLOW RAPID SEED PRODUCTION LOWEST LOW HIGH

37 Evolution does not work this way

38 LAB: Natural Selection
(Birds on an Island) Purpose: Explore how the frequencies of three beak phenotypes change over several generations in a population of bird on an island.

39 Lab Report Format Title Group Members Benchmark Problem Introduction
Hypothesis Variables Data


Similar presentations

Ads by Google