Transcript Energy

Please feel free to chat amongst yourselves
until we begin at the top of the hour.
Seminar Agenda
 Population Genetics
 Seminar Discussion Questions
 Questions & Answers
Population Genetics
• Population genetics = application of genetic principles
to entire populations of organisms
• Population = group of organisms of the same species
living in the same geographical area
• Subpopulation = any of the breeding groups within a
population among which migration is restricted
• Local population = subpopulation within which most
individuals find their mates
3
Population Genetics
• Gene pool = the complete set of genetic
information in all individuals within a population
• Genotype frequency = proportion of individuals in
a population with a specific genotype
• Genotype frequencies may differ from one
population to another
• Allele frequency = proportion of any specific allele
in a population
• Allele frequencies are estimated from genotype
frequencies
4
Mating Systems
• Random mating means that mating pairs are
formed independently of genotype
• Random mating of individuals is equivalent of the
random union of gametes
• Assortative mating = nonrandom selection of
mating partners; it is positive when like
phenotypes mate more frequently than would be
expected by chance and is negative when reverse
occurs
• Inbreeding = mating between relatives
5
Hardy–Weinberg Principle
• When gametes containing either of two alleles, A or a,
unite at random to form the next generation, the
genotype frequencies among the zygotes are given by
the ratio
p2 : 2pq : q2
this constitutes the Hardy–Weinberg (HW) Principle
p = frequency of a dominant allele A
q = frequency of a recessive allele a
p + q =1
6
Fig. 14.10
7
Hardy–Weinberg Principle
• One important implication of the HW Principle is
that allelic frequencies will remain constant over
time if the following conditions are met:
• The population is sufficiently large
• Mating is random
• Allelic frequencies are the same in males and
females
• Selection does not occur = all genotypes have
equal in viability and fertility
• Mutation and migration are absent
8
Hardy–Weinberg Principle
• Another
important
implication is
that for a rare
allele, there are
many more
heterozygotes
than there are
homozygotes
for the rare
allele
Fig. 14.12
9
Hardy–Weinberg Principle
• HW frequencies can be extended to multiple
alleles:
Frequency of any homozygous genotype = square
of allele frequency = pi2
Frequency of any heterozygous genotype = 2 x
product of allele frequencies = 2pipj
10
Hardy–Weinberg Principle
• X-linked genes are a
special case because
males have only one Xchromosome
• Genotype frequencies
among females: HH = p2 ;
Hh = 2pq; hh = q2
• Genotype frequencies
among males are the same
as allele frequencies:
H = p,
h=q
Fig. 14.15
11
Discussion Question 1:
 14.7: A condition called nonsyndromic recessive
auditory neuropathy results in deafness. One form is
caused by a recessive autosomal gene. The frequency
of affected individuals due to the mutant gene in one
population is 0.003. Assuming Hardy-Weinberg
equilibrium, what is the expected incidence of the
disorder among the offsprings of matings in which
both parents are heterozygous carriers?
Discussion Question 1:
 Answer: The expected frequency is 0.25 or 25%.
This question does not require calculations using p
and q. It is only necessary to recognize that the
matings are of two heterozygous carriers, Aa X Aa,
and, therefore, the expected frequency of aa
offspring is 25%.
Discussion Question 2:
 14.9: How does the recessive allele that
causes Tay-Sachs disease survive in a
population if all affected individuals die
before they can reproduce?
Discussion Question 2:
 Answer: Two issues need to be considered. First
recessive alleles are maintained in heterozygous
individuals and so are not exposed to selection.
Second, new mutations in each generation
replenish the number eliminated by selection in
homozygous recessives.
Discussion Question 3a:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (a) Any specified homozygous genotype?
Discussion Question 3a:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (a) Any specified homozygous genotype?
 Answers: (1/n)2 = 1/n2
 Frequency of any homozygous genotype = square of allele
frequency
Discussion Question 3b:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (b) Any specified heterozygous genotype?
Discussion Question 3b:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (b) Any specified heterozygous genotype?
 Answer: 2 (1/n)(1/n) = 2/n2
 Frequency of any heterozygous genotype = 2 X product of
allele frequencies
Discussion Question 3c:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (c) All homozygous genotypes together?
 Answers: n(1/n)2 = 1/n
Discussion Question 3d:
 14.11: Suppose a randomly mating diploid population
has n equally frequent alleles of an autosomal locus.
What is the expected frequency of:
 (d) All heterozygous genotypes together?
 Answer: [n(n-1)/2] X (2/n2) = 1 – (1/n)
Any questions?