Download Modern Theory of Evolution

Modern Theory of Evolution
Modern Theory of Evolution
Hugo De Vries – botanist and geneticist
 Recognized that organisms of different species still
share common phenotypes
 Concluded that there must be
common genes in varied species.
 In the early 1900’s, through
observations of new forms of flower
species, he introduce the concept
of mutations.
Modern Theory of Evolution
Hugo De Vries – botanist and geneticist
 Mutation Theory stated that
“mutations are the ultimate
source of variation”
 It was later indicated that
recombination during
sexual reproduction and
migration are also important
factors.
Modern Theory of Evolution
 Individuals do not evolve but entire populations evolve
if genetic make-up of the whole population is varied.
 The key to this is the importance of populations.
 A population is a group of organisms of the same
species living together within a particular region.
A couple of Terms to sum it up.
Allele Frequency – The number of particular alleles
within a population.
Gene Pool – The total of all the types of alleles in a
population.
 Each allele occurs with a certain frequency.
 These frequencies may change as a result of natural
selection.
 Therefore, evolution is a gradual change of allele
frequencies in a population.
Hardy-Weinberg Law
In 1908 Godfrey Harold Hardy and Wilhelm Weinberg
showed that the segregation and recombination of
genes in sexual reproduction could not by itself
change the allele frequencies.
Ex. Allele p=90%
Allele q = 10%
The Law
- Ordinary random mating
always produce the same
frequencies.
Hardy-Weinberg Law
For this constant allele frequency to occur,
the following must be true:
The population must be large.
2. Individuals must not migrate into or out.
3. Mutations must not occur.
4. Reproduction must be random
1.
# 1 & 2 may exist
# 3 & 4 almost never exist
Hardy-Weinberg Law
So what is the big deal???
 Enables us to demonstrate that evolution is
occurring.
 The fact that populations change tells us
that external factors cause the change.
 Failure of the law is considered evidence of
Evolution.
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
p = frequency of one allele of a trait
q = frequency of the other allele of the trait
Frequency of homozygous dominant (TT) ---- p2
Frequency of heterozygous dominant (Tt) ---- 2pq
Frequency of homozygous recessive (tt) ---- q2
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
If the frequency of the widows peak allele is 70% and the
non-widows peak allele is 30%
(O.70)2 + 2(0.70)(0.30) + (0.30)2 = 1
0.49 + 0.42 + 0.09 = 1
1=1
See, it works!!
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
 This can be used to find the exact allele frequencies in
the population.
 You need to know the percent of individuals with the
recessive phenotype.
 If the allele frequencies are found to change over time
(which does happen all the time), then this is seen as
evidence of evolution.
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
Find the allele and genotype frequencies if the
frequency of tongue rollers is 75% and non-tongue
rollers is found to be 25%.
q2 = 0.25
Because p
+q=1
q = 0.5
p = 0.5
p2 = 0.25
2pq = 0.5
tt = 25%
tT = 50%
TT = 25%
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
Find the allele and genotype frequencies if the
frequency of spotted frogs (S) is 64% and non-spotted
frogs (s) is found to be 36%.
q2 = 0.36
Because p
+q=1
q = 0.6
p = 0.4
p2 = 0.16
2pq = 0.48
tt = 36%
tT = 48%
TT = 16%
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
Recall that if the allele frequencies are found to change over
time, then this is seen as evidence of evolution.
Suppose that in a population of salamanders, a
dominant allele is for a horned snout and the
recessive allele is for a blunt snout. If in 1985,
98% of the population had the horned snout and
today, the horned snout population was found to
be only 65%. Find the percent change in the
allele frequencies and describe what could
account for this change.
Hardy-Weinberg Principle
p2 + 2pq + q2 = 1
Suppose that in a population of salamanders, a dominant allele is for a horned snout
and the recessive allele is for a blunt snout. If in 1985, 98% of the population had the
horned snout and 25 years later, the horned snout population was found to be only
65%. Find the percent change in the allele frequencies and describe what could
account for this change.
1985 q2 = 0.02
2010 q2 = 0.35 There has been
q = 0.1414
p = 0.8586
q = 0.5916
p = 0.4084
a 45% change
in the allele
frequencies.
The change in allele frequency is considered evidence of
evolution. This could be due to a whole number of factors. A
likely factor could be food availability and the blunt snout
making it easier to eat a particular food.