Genes and DNA. 1) Natural Selection. 2) Mutations. Darwin knew this

Transcription

1 1) Natural Selection The mechanism (driving force) for evolution, as explained by Charles Darwin. Explains changes in an entire species or population (not individuals) over time. 2) Mutations Random changes in DNA are sometimes passed on to offspring. Some helpful; some harmful; some neutral Only traits that increase reproductive fitness will continue to be passed on. Darwin knew this Darwin didn t know this because he didn t know about Genes and DNA

2 Darwin recognized that limited resources in any environment lead to a struggle for existence, in which the traits of some individuals will give them an advantage over others. However slight this advantage, it will lead to certain traits being selected by nature to survive and reproduce Hence, natural selection!

3 NATURAL SELECTION DEFINITION: the process by which organisms that are better suited to an environment survive and reproduce in greater number than those less suited. What causes natural selection? Environmental Change Survival of the Fittest (But what is fit????) Categorized into 5 Steps Whatever traits help you survive and/or reproduce

4 When we say competition Two men are walking through a forest. Suddenly, they see a tiger in the distance, running towards them. They turn and start running away. But then one of them stops, takes some running shoes from his bag, and starts putting them on. What are you doing? says the other man. Do you think you will run fast than the tiger with those? I don t have to run faster than the tiger, he says. I just have to run faster than you. who is competing with whom?

5 What is meant by fitness? Is this fitness?

6 STEP 1: Variation Different traits within a population or species; No two have the exact same DNA *the total of all alleles (or variations) in the population is called a gene pool

7 STEP 1: Variation Variations within a population come from mutations & random mating changing the populations gene pool MUTATIONS: Changes in an organisms DNA or genes (Darwin was missing this key info on genetics) RANDOM MATING: mixing of genes through reproduction A change in the gene for feather color creates different alleles which creates different coloration of bird feathers in the population VARIATIONS IN BIRD COLOR: Most birds are born with traits (genes) for being blue-green in color. Occasionally some birds are born with traits that make them more green. Occasionally some birds are born with traits that make them more blue.

8 STEP 2: Inheritance Traits are passed down from one generation to the next through genes. VARIATIONS IN BIRD COLOR: Most birds are born with traits (genes) for being blue-green in color. Occasionally some birds are born with traits that make them more green. Occasionally some birds are born with traits that make them more blue.

9 STEP 3: Selection Organisms compete for resources such as food, shelter, and mates. Certain traits are selected by nature because they help organisms survive and reproduce better than others. The birds face the challenge of blending in to survive.

10 STEP 3: Selection Ugh!, so full Not all members of the species will survive this competition. Only some will survive and have the opportunity to pass on their successful genes. Since blue-green birds stand out more in the habitat than green birds, more blue-green birds are eaten EEP!

11 STEP 4: Time Successful traits are passed to the next generation. Now, more members of the population are being born with the successful variation than those with the less suited allele. Given enough time over many generations, small, gradual changes become big changes How has the allele frequency in the population changed? Now more green chicks than blue/ blue-green are being born.

12 ? STEP 5: Adaptation of the Species Now the entire species becomes better suited to its environment. New beneficial traits arise as a population becomes suited to its environment, diet, and way of life. Hee, hee

13 Variation Different traits within a population or species; No two have the exact same DNA. Inheritance Selection Time Adaptation Traits are passed down from one generation to the next through genes. Certain traits are selected by nature because they help organisms survive and reproduce better than others. Given enough time over many generations, small, gradual changes become big changes. New beneficial traits arise as a population becomes suited to its environment, diet, and way of life.