Modern Theory of Modern Theory of Evolution…Evolution…Part4Part4

I. Darwin’s Weakness• Couldn’t explain why there was

variation in populations. Didn’t understand genetics! Mendel’s theory was only dominant/recessive

• How do new characteristics appear?• Mutations• Sexual reproduction

II. Modern Theory of EvolutionII. Modern Theory of Evolution• Darwin’s theory of Natural Selection

with Genetics!

+

III. Population GeneticsIII. Population Genetics

• Species: A group of organisms that look alike and are capable of reproducing and creating fertile offspring.

• Population: A group of individuals of the same species living in the same place at the same time.– Ex: homo sapiens in Hawaii– Ex: Stray cats at Kalaheo High School

Population…continuedPopulation…continued– Can an individual respond

to environmental change by adding or losing a trait?• No, evolution is a change in a

species over a long period of time in response to environmental changes.

– Populations evolve, not individuals!!

Population Genetics…contPopulation Genetics…cont• Gene Pool:

All the genes in a population at any given time.

• Allele Frequency: Occurrence of alleles in a population – Remember, alleles are different forms

of the same trait.

IV. Adaptive Value IV. Adaptive Value ProblemsProblems• Step 1: Define the population & count it!

– ____Homo sapiens in this classroom

• Step 2: Define the trait and alleles.– Trait: tongue rolling– Alleles: R-tongue roller, r-non tongue roller

• Step 3: count up the genotypes in your population and the totals of each alleles.– RR:_______ Rr:______ rr: ______

Total R: ______ Total r:______ Total alleles:________

• Step 4: Determine the gene frequency of each allele.– Gene frequency of “R” =(# of R)/ Total– Gene frequency of “r” = (# of r )/ Total

Let’s try another example…Let’s try another example…• Step 1: ____Homo sapiens in this

classroom• Step 2: ____PTC tasting…T: taster, t:

non-taster• Step 3: TT:_____ Tt:_____ tt:_____ Total T:____ Total t:___ Total alleles______• Step 4: Determine the gene frequency for

“T” and “t”

V. V. So why do these FUN So why do these FUN problems?problems?

• Adaptive Values: The value traits have in helping an organism survive.

– Allele frequency is the same thing*High Value-90% *Medium value-50% * Low value-10%

Camouflage in a tree frog Tongue rolling in humans Six fingers in humans

Adaptive Adaptive Values…contValues…cont..The more variety in a species (even neutral

variations), the greater chance for..

1. Survival… Environment is always changing2. Variation fights off extinction

Once trait is lost…

1. It is really hard for a species to get it back.2. Traits may not be useful now, but who

knows what will be needed in the future to survive.