1. A. How Common is Genetic Variation? B. Variation and Gene Pools
Section Outline
Section 16-1
16–1 Genes and Variation
A. How Common is Genetic Variation?
B. Variation and Gene Pools
C. Sources of Genetic Variation
1. Mutations
2. Gene Shuffling
D. Single-Gene and Polygenic Traits

2. 16-1 Genes and Variation Variation and Gene Pools
A _________ consists of all the genes present in a population, including all the different ______. The _______
________ is the number of times an allele occurs in the gene pool compared to the occurrence of other alleles in the gene pool.
alleles
relative
frequency

3. Figure 16–2 Relative Frequencies of Alleles
Section 16-1
It’s pretty easy
to count up the
phenotype. Just
count the black
mice and the
brown mice…
Sample Population
48% heterozygous black
36% homozygous brown
16% homozygous black
Frequency of Alleles
allele for brown fur
allele for black fur
…but since the homozygous dominant and the heterozygous genotypes share the same phenotype, it’s hard to know the frequency of the genotypes, and the alleles. That’s where Hardy & Weinberg come in…

4. Who? Hardy & Weinberg Godfrey Hardy Wilhelm Weinberg 1877-1947
They developed an equation that predicted the relative frequency of alleles in a population based on the frequency of the phenotypes in a population, which are
a lot easier to count…

5. Gene Frequency & the Hardy-Weinberg Equation
p pq + q2 = 1
p2 = the frequency of homozygous dominant genotype
2pq = the frequency of heterozygous genotype
q2 = the frequency of homozygous recessive genotype

6. Hardy-Weinberg & the Frequency of Albinism
________ is a rare _________ trait in
humans and other animals. In humans, only 1 in 20,000 people demonstrate the trait. To be an ______, a person has to have a __________ _________
genotype, or __.
Albinism
recessive
albino
homozygous
recessive aa

7. Hardy-Weinberg & the Frequency of Albinism
According to the _____-________ equation, __ = the frequency of the homozygous recessive genotype, which in the case of albinism is _______, or _______. If __ = _______, then _ = _______, or ______.
Hardy
Weinberg q2
1/20,000 q2 q √

8. Hardy-Weinberg & the Frequency of Albinism
If _ = ______, and _ + _ = _, or _____, then _ = _______. (Remember, q = the frequency of a, and p = the frequency of A, A + a = 100%) So about _____ of all the alleles in the population are _, and only about ____ of the alleles in the population are _. q q p 1
100% p
99.3% A
0.7% a

9. Hardy-Weinberg & the Frequency of Albinism
Finally, if __ + ___ + __ = _, and
_ = _______, and _ = _______, then
__ = __________________________ _______________ = __________ = _______, and ___ = _____________ ______________________ = ________________ = _______, and p2
2pq q2 1 q p
the frequency of the homozygous p2
dominant genotype
( )2
2pq
the frequency of
the heterozygous genotype
2( )( )

10. Hardy-Weinberg & the Frequency of Albinism
__ = = ________________
__________________________ =
_________ = _______. In albinism
then, _____ of the population is
__________________, ____ of the
population is ____________, and _____
of the population is __________
________.
the frequency of the
homozygous recessive genotype
( )2
98.6%
homozygous dominant
1.4%
heterozygous
.005%
homozygous
recessive

11. Relative Frequencies of Alleles
Sample Population
48% heterozygous black
36% homozygous brown
16% homozygous black
Frequency of Alleles
allele for brown fur
allele for black fur

12. Relative Frequencies of Alleles
16% Homozygous 48% Heterozygous 36% Homozygous
Black Mice Black Mice Brown Mice
BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb
BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb
BB BB BB BB Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb
Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb
Bb Bb Bb Bb Bb Bb
________________ ________________ ________________
32 B’s 48 B’s, 48 b’s 72 b’s
80/200 x = 40% B
120/200 x 100 = 60% b
= 80 B’s
= 120 b’s
= 200 B’s & b’s
REMEMBER THESE TWO NUMBERS! LET’S SEE IF HARDY & WEINBERG
GET THE SAME ANSWERS.

13. Hardy-Weinberg & the Frequency of Coat Color in Mice
If __ + ___ + __ = _, and __ = ___
_______________________________ ________, then __ = ___ or ____, and
___ = _______________________
____________, = ____, or ____, and
__ = __________________________ ________________ = ____,or ____. p2
2pq q2 1
the p2
frequency of the homozygous dominant
genotype p2
16%
0.16
2pq
the frequency of the hetero-
gous genotype
48%
0.48 q2
the frequency of the homozygous
recessive genotype
36%
0.36

14. Hardy-Weinberg & the Frequency of Coat Color in Mice
If __ = ____, then _ = _____ = ____
and if __ = ____, then _ = _____ =
____. __________ are easy to observe
and count. The Hardy-Weinberg
equation allows us to go from the
__________ to the frequency of the
_____ that cause them. p2
0.16 p
√0.16
0.40 q2
0.36 q
√0.36
0.60
Phenotypes
phenotypes
alleles

15. Hardy-Weinberg & the Frequency of Coat Color in Mice
Any change in the relative frequency of
alleles in a population is ________.
evolution

16. Sources of Genetic Variation
A ________ is any change in a
a sequence of ____, due to mistakes
the nucleus makes in _________ or
due to exposure to ________ or
________ in the environment. Most
________ are _____, but some cause
changes in the ____ that affect
an organism’s ______.
mutation
DNA
replication
radiation
chemicals
mutations
lethal
DNA
fitness

17. ____________________ during __________ of _______ is a lot like
Gene Shuffling
____________________ during
__________ of _______ is a lot like
shuffling a deck of cards. There is
always 52 cards, and the _________
of you being dealt any one card is
always the same.
Independent assortment
Anaphase I
meiosis
probability

18. During ____________________, there are 23 ___________ “cards” that
Gene Shuffling
During ____________________,
there are 23 ___________ “cards” that
can be “shuffled” and “dealt” in
_________ combinations! Also,
sometimes the “cards” you are dealt
are brand-new and unique due to
___________.
independent assortment
chromosome
8.4 million
crossing over

19. Monogenic vs. Polygenic Traits
The more _____ that control a trait, the
more __________ are possible. A
widow’s peak is controlled by ___ gene
with ___ alleles. Possible _________
include ___, ___, and ___, with widow’s
peak being ________. There are ___
__________. You either have one, or
you don’t.
genes
phenotypes
one
two
genotypes WW Ww ww
dominant
two
phenotypes

20. Figure 16–3 Phenotypes for Single-Gene Trait
Section 16-1
Challenge: If 36% of the human population have
a widow’s peak, and 64% don’t have a widow’s
peak, what is the relative frequency of the recessive
allele, w, and the dominant allele W, according to
Hardy-Weinberg? What percentage are heterozygous?
100 80 60 40 20
Answer
Frequency of Phenotype
(%)
p pq + q2 = 1
q2 = 64% = 0.64 ww
q = √.64 = 0.80 = 80%
q + p = 1
p = = 20% W
2pq = 0.32 = 32% Ww
Widow’s peak
No widow’s peak
Phenotype

21. Monogenic vs. Polygenic Traits
_____________ are controlled by
___ or ____ genes. Human height is
controlled by _____ genes and ___
alleles. There are _____ possible
__________. The _______________
shows that once again nature seems to
favor ______, because it produces the
most ______.
Polygenic traits
two
more
three
six
seven
phenotypes
normal distribution
medium
variety

22. Generic Bell Curve for Polygenic Trait
Section 16-1
HhGgTt
HhGgtt
HHGgTt
Hhggtt
HHGGTt
hhggtt
HHGGTT
Frequency of Phenotype
Phenotype (height)