Friday, February 4, 2011

Feb 1st

Today, we went over answers to UP pgs. 17A-E and notes.


Modern synthesis: the fusion of genetics with biology

Modern synthesis is a study of variations in populations caused by mutations and sexual recombination.

Population: group of SAME SPIECIES living in same area at same time (Important!)

Gene Pools: all of the alleles in all the individuals making up a population (how many big and small alleles)

Allele: form a trait

Ex: Wildflower with only two varieties-

Red flowers = R & white flowers = r

Suppose 80% or .8 of all flowers in the gene pool have the R allele.

p = relative frequency (how common something is) of the dominant allele (R), so p = .8

q = frequency of the recessive allele (r), so q = .2


Since there are only two alleles for flower color, then p+q=1 (MEMORIZE FOR TEST)!

Now that we know the formula, we can find the frequencies of the different genotypes in the population IF the gene pool is completely stable (non-evolving).

Meaning, no one can leave or join the population.

This is called the Hardy-Weinberg equilibrium.

G.H. Hardy questioned, “How can both dominant and recessive alleles remain in populations? Why don’t dominants simply drive out recessives?”

It was discovered that genetic recombination does not by itself change the overall composition of the gene pool. They examined the behavior of alleles in an idealized population in which five conditions hold:

1. No mutations occur

2. No net movement of individuals in or out of the population

3. Population is large enough

4. Mating is random

5. All alleles are equally viable (no natural selection)

• Ex: Dwarfism -> Aa = Dwarf aa = normal AA = too much dwarfism in you, you can’t survive

This ideal environment is hard to find.

Now, back to the wildflower problem!

What’s the probability of producing an RR individual by “drawing” two R alleles from the pool of gametes?

R sperm x R egg (p x p) -> .8 x .8 = .64, or 64% of the plants in the population will have the RR genotype.

Well then, what is the frequency of rr individuals in the population?

r x r (q x q) -> .2 x .2 = .04, or 4% of the plants in the population will have the rr genotype.

What is the frequency of Rr in the population?

Rr + rR, or 2pq

2 (.8 x.2) = .32, or 32% are Rr with red flowers.

General formula: p^2+2pq+q^2=1 (MEMORIZE)!

You can use a Punnett Square to solve the problem as well.

Tonight’s homework:  UP pgs. 31-36 due Thursday

Next Scribe: Christine K.

1 comment:

  1. This was really helpful! and another tip to help remember that formula is that it is the same as the quadratic formula in math class just with the letters p and q instead of a and b.