Transcript ppt - Furman University

BIO 221: GENETICS
Modern Biology: What Life Is and How It Works
I. Overview
- Darwin (1859) Origin of Species
- Mendel (1865) Experiments in Plant Hybridization
- Flemming (1878) Describes chromatin and mitosis
II. Darwin’s Contributions
A. Life
- Born Feb 12, 1809
- Graduated Cambridge, intending to join the clergy
- 1831-36, Naturalist on H.M.S. Beagle
- 1859: The Origin of Species
- Died April 19, 1882, interred in Westminster Abbey
II. Darwin’s Contributions
B. His Theories
1. Evolution ‘proper’ – species change
2. Evidence:
a. Change in domesticated
animals and plants over time
II. Darwin’s Contributions
B. His Theories
1. Evolution ‘proper’ – species change
Evidence:
b. Changes in lineages in the
fossil record
II. Darwin’s Contributions
B. His Theories
2. Common Ancestry - Species are “related by
descent” and have diverged from one another
From his second notebook
on the transmutation of
species - 1837
From The Origin of Species - 1859
II. Darwin’s Contributions
B. His Theories
2. Common Ancestry – Species are “related by
descent” and have diverged from one another
Evidence:
Homologous Structures
Vestigial Structures
II. Darwin’s Contributions
B. His Theories
2. Common Ancestry – Species are “related by
descent” and have diverged from one another
Evidence:
Embryology
Whale embryo w/leg buds
photo
Haeckel
The historical fact of evolution – that organisms are biologically
related to one another - is the foundational theory of all
biological sciences… including medicine:
Dr. Neil Shubin, Department of Anatomy, University of Chicago
II. Darwin’s Contributions
B. His Theories
3. Natural Selection – HOW species change
P1: All populations have the capacity to ‘over-reproduce’
P2: Resources are finite
C: There will be a “struggle for existence”… most offspring born will die
before reaching reproductive age.
P3: Organisms in a population vary, and some of this variation is heritable
C2: As a result of this variation, some organisms will be more likely to
survive and reproduce than others – there will be differential reproductive
success.
C3: The population change through time, as adaptive traits accumulate in
the population.
Corollary: Two populations, isolated in different environments, will diverge
from one another as they adapt to their own environments. Eventually,
these populations may become so different from one another that they are
different species.
II. Darwin’s Contributions
B. His Theories
3. Natural Selection – HOW species change
Evidence:
1. Divergence in domesticated animals, with humans acting as the selective
agent - deciding who gets to breed (“artificial selection”)
II. Darwin’s Contributions
B. His Theories
3. Natural Selection – HOW species change
Evidence:
2. Divergence in wild animals, with differences related to different roles in the
environment (adaptations).
"Seeing this gradation and diversity of
structure in one small, intimately related
group of birds, one might really fancy that
from an original paucity of birds in this
archipelago, one species had been taken
and modified for different ends.“ – Charles
Darwin, The Voyage of the Beagle (1839)
II. Darwin’s Contributions
B. His Theories
3. Natural Selection – HOW species change
Evidence:
3. Convergence in traits for organisms experiencing the same environment.
Homologous bones are color-coded, but the wing is made from different parts, and
thus, while similar functionally, the wings are analogous.
II. Darwin’s Contributions
B. His Theories
3. Natural Selection – HOW species change
Evidence:
3. Convergence in traits for organisms
experiencing the same environment.
South America
(Placentals)
Australia
(Marsupials)
II. Darwin’s Contributions
C. His Dilemmas
“Long before having arrived at this part of my work, a crowd of difficulties will
have occurred to the reader. Some of them are so grave that to this day I can
never reflect on them without being staggered; but, to the best of my judgment,
the greater number are only apparent, and those that are real are not, I think,
fatal to my theory.” – Charles Darwin, The Origin of Species (1859), “Chapter
VI: Difficulties of the Theory”.
II. Darwin’s Contributions
C. His Dilemmas
1. The evolution of complex structures
“Can we believe that natural selection
could produce, on the one hand, organs of
trifling importance, such as the tail of a
giraffe, which serves as a fly-flapper, and,
on the other hand, organs of such
wonderful structure, as the eye, of which
we hardly as yet fully understand the
inimitable perfection?”– Charles Darwin,
The Origin of Species (1859).
II. Darwin’s Contributions
C. His Dilemmas
1. The evolution of complex structures
“To suppose that the eye, with all its inimitable contrivances for adjusting the
focus to different distances, for admitting different amounts of light, and for the
correction of spherical and chromatic aberration, could have been formed by
natural selection, seems, I freely confess, absurd in the highest possible degree…”
II. Darwin’s Contributions
C. His Dilemmas
1. The evolution of complex structures
“To suppose that the eye, with all its inimitable contrivances for adjusting the
focus to different distances, for admitting different amounts of light, and for the
correction of spherical and chromatic aberration, could have been formed by
natural selection, seems, I freely confess, absurd in the highest possible degree.
Yet reason tells me, that if numerous gradations from a perfect and complex eye
to one very imperfect and simple, each grade being useful to its possessor, can be
shown to exist; if further, the eye does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any variation or modification in the
organ be ever useful to an animal under changing conditions of life, then the
difficulty of believing that a perfect and complex eye could be formed by natural
selection, though insuperable by our imagination, can hardly be considered real.
Charles Darwin, The Origin of Species (1859).
II. Darwin’s Contributions
C. His Dilemmas
1. The evolution of complex structures
Dawkins: Evolution of the Camera Eye
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates between living species, and the lack of complete
transitional sequences in the fossil record
“…why, if species have descended from other species by insensibly fine
gradations, do we not everywhere see innumerable transitional forms? Why is
not all nature in confusion instead of the species being, as we see them, well
defined? … as by this theory innumerable transitional forms must have
existed, why do we not find them embedded in countless numbers in the crust
of the earth?” – Charles Darwin, The Origin of Species (1859)
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
?
X
X
X
X
?
X
X
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
“As natural selection acts solely by the preservation of profitable
modifications, each new form will tend in a fully-stocked country to take the
place of, and finally to exterminate, its own less improved parent or other
less-favoured forms with which it comes into competition. Thus extinction
and natural selection will, as we have seen, go hand in hand. Hence, if we
look at each species as descended from some other unknown form, both the
parent and all the transitional varieties will generally have been exterminated
by the very process of formation and perfection of the new form.” –The
Origin of Species (Darwin 1859)
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
X
X
Better adapted
descendant
outcompetes
ancestral type
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
X
X
X
Better adapted
descendant
outcompetes
ancestral type
X
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
X
X
X
X
Better adapted
descendant
outcompetes
ancestral type
X
X
II. Darwin’s Contributions
C. His Dilemmas
“I believe the answer mainly lies in the record
being incomparably less perfect than is generally
supposed.” The Origin of Species (Darwin 1859)
2. The lack of intermediates
?
X
X
X
X
X
X
II. Darwin’s Contributions
C. His Dilemmas
2. The lack of intermediates
1861 – Archaeopteryx lithographica
“…and still more recently, that strange bird,
the Archeopteryx, with a long lizardlike tail,
bearing a pair of feathers on each joint, and
with its wings furnished with two free claws,
has been discovered in the oolitic slates of
Solenhofen. Hardly any recent discovery
shows more forcibly than this, how little we as
yet know of the former inhabitants of the
world.” – Charles Darwin, The Origin of
Species, 6th ed. (1876)
II. Darwin’s Contributions
C. His Dilemmas
3. What is the source of heritable variation?
II. Darwin’s Contributions
C. His Dilemmas
3. What is the source of heritable variation?
- Inheritance of acquired characters – (wrong)
- Use and disuse – (sort of, but not as he envisioned it)
Jean Baptiste Lamarck (1744-1829)
"It is interesting to contemplate an entangled bank,
clothed with many plants of many kinds, with birds
singing on the bushes, with various insects flitting
about, and with worms crawling through the damp
earth, and to reflect that these elaborately constructed
forms, so different from each other, and dependent on
each other in so complex a manner, have all been
produced by laws acting around us. These laws, taken
in the largest sense, being Growth with Reproduction;
Inheritance which is almost implied by reproduction;
Variability from the indirect and direct action of the
external conditions of life, and from use and disuse; a
Ratio of Increase so high as to lead to a Struggle for
Life, and as a consequence to Natural Selection,
entailing Divergence of Character and the Extinction of
less-improved forms. Thus, from the war of nature,
from famine and death, the most exalted object which
we are capable of conceiving, namely, the production
of the higher animals, directly follows. There is
grandeur in this view of life, with its several powers,
having been originally breathed into a few forms or into
one; and that, whilst this planet has gone cycling on
according to the fixed law of gravity, from so simple a
beginning endless forms most beautiful and most
wonderful have been, and are being, evolved". - The
Origin of Species (Darwin 1859).
II. Darwin’s Contributions
D. Darwin’s Model of Evolution
3. What is the source of heritable variation?
SOURCES OF VARIATION
?
AGENTS OF CHANGE
V
A
R
I
A
T
I
O
N
Natural Selection
Modern Biology
I. Overview
II. Darwin’s Contributions
III. Mendel's Contributions
III. Mendel's Contributions
A. Mendel’s Life:
- Born July 20, 1822 in Czech Rep.
- Entered Augustinian Abbey in Brno – 1843
III. Mendel's Contributions
A. Mendel’s Life:
- 1856-63: tested 29,000 pea plants
- 1866: Published “Experiments on Plant
Hybridization”, which was only cited 3 times
in 35 yrs
- Died Jan 6, 1884 in Brno.
III. Mendel's Contributions
A. Mendel’s Life:
B. Pre-Mendelian Ideas About Heredity
Traits run in families….
III. Mendel's Contributions
A. Mendel’s Life:
B. Pre-Mendelian Ideas About Heredity
1. Preformationist Ideas
OVIST
HOMUNCULAN
III. Mendel's Contributions
A. Mendel’s Life:
B. Pre-Mendelian Ideas About Heredity
1. Preformationist Ideas
2. Epigenetic Ideas
?
III. Mendel's Contributions
A. Mendel’s Life:
B. Pre-Mendelian Ideas About Heredity
1. Preformationist Ideas
2.
Epigenetic Ideas
3.
Blending Heredity
III. Mendel's Contributions
A. Mendel’s Life:
B. Pre-Mendelian Ideas About Heredity
C. Mendel’s Experiments
C. Mendel’s Experiments
1. Monohybrid Experiments
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
Pollen (purple)
Ovule (white)
WHY??
Ovule (purple)
Pollen (white)
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
Pollen (purple)
PARENTAL CROSS
Ovule (white)
Ovule (purple)
Pollen (white)
Results falsified both the ovist and homunculan schools – hereditary
information must come from both parents….
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
Decided to cross the offspring in an F1 x F1
cross:
Got a 3:1 ratio of purple to white…. (705:224)
SO, the F1 Purple flowered plant had particles
for white that were not expressed, but could
be passed on.
- Proposed 4 ‘postulates’
(hypotheses) to explain his data:
1) hereditary material is
“particulate”
- Proposed 4 ‘postulates’
(hypotheses) to explain his data:
1) hereditary material is
“particulate”…. and each organism
has 2 particles governing each trait
- Proposed 4 ‘postulates’
(hypotheses) to explain his data:
1) hereditary material is
“particulate”…. and each organism
has 2 particles governing each trait
2) if the particles differ, only one
(‘dominant’) is expressed as the
trait; the other is not expressed
(‘recessive’).
- Proposed 4 ‘postulates’
(hypotheses) to explain his data:
1) hereditary material is
“particulate”…. and each organism
has 2 particles governing each trait
2) if the particles differ, only one
(‘dominant’) is expressed as the
trait; the other is not expressed
(‘recessive’).
3) during gamete formation, the two
particles governing a trait SEPARATE
and go into DIFFERENT gametes…
- Proposed 4 ‘postulates’
(hypotheses) to explain his data:
1) hereditary material is
“particulate”…. and each organism
has 2 particles governing each trait
2) if the particles differ, only one
(‘dominant’) is expressed as the
trait; the other is not expressed
(‘recessive’).
3) during gamete formation, the two
particles governing a trait SEPARATE
and go into DIFFERENT gametes.
Subsequent fertilization is RANDOM
(these gametes are equally likely to
meet with either gamete type of the
other parent…and vice-versa). This
is Mendel’s Principle of Segregation
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
½W
Ww
Based on his hypotheses
(postulates), the plant should
produce two types of gametes at
equal frequency.
½w
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
HOW can we see these
frequencies, when we can only
actually observe the phenotypes
of the offspring?
Mate with the
recessive parent,
which can only give
recessive alleles to
offspring
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
ww
w
½W
Ww
½w
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
Mate with the
recessive parent,
which can only give
recessive alleles to
offspring
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
ww
w
½W
½ Ww
Ww
½w
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
½ ww
Genotypic
Ratio of
offspring
Mate with the
recessive parent,
which can only give
recessive alleles to
offspring
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
ww
w
½W
½ Ww
½W
½ ww
½w
Ww
½w
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
Genotypic
Ratio of
offspring
Phenotypic
Ratio of
offspring
Mate with the
recessive parent,
which can only give
recessive alleles to
offspring
C. Mendel’s Experiments
1. Monohybrid Experiments
a. reciprocal crosses
b. crossing the F1 hybrids
c. Proposed four postulates
2. Monohybrid Test Cross
ww
w
Same as gamete
frequencies of
unknown parent
½W
½ Ww
½W
½ ww
½w
Ww
½w
Mendel’s ideas rested on the
hypothesis that the F1 plants
were hiding a gene for ‘white’
Hypothesized Genotype = Ww
Genotypic
Ratio of
offspring
Phenotypic
Ratio of
offspring
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
Round and Yellow Peas
Wrinkled and Green Peas
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
Round and Yellow Peas
Wrinkled and Green Peas
RRYY
rryy
RY
ry
100% F1 = RrYy
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
b. F1 x F1 cross
X
RrYy
RrYy
315 round, yellow (~9/16)
108 round, green (~3/16)
101 wrinkled, yellow (~3/16)
32 wrinkled, green (~1/16)
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
b. F1 x F1 cross
X
RrYy
RrYy
Monohybrid Ratios Preserved
315 round, yellow (~9/16)
423 Round (~3/4)
108 round, green (~3/16)
~ 3:1
101 wrinkled, yellow (~3/16)
133 wrinkled (~1/4)
32 wrinkled,green(~1/16)
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
b. F1 x F1 cross
X
RrYy
RrYy
Monohybrid Ratios Preserved
315 round, yellow (~9/16)
416 Yellow (~3/4)
108 round, green (~3/16)
~ 3:1
101 wrinkled, yellow (~3/16)
140 Green (~1/4)
32 wrinkled, green (~1/16)
C. Mendel’s Experiments
1. Monohybrid Experiments
2. Monohybrid Test Cross
3. Dihybrid Experiments
a. Parental cross
b. F1 x F1 cross
c. His explanation
Mendel's Principle of Independent Assortment:
During gamete formation, the way one pair of
genes (governing one trait) segregates is not
affected by (is independent of) the pattern of
segregation of other genes; subsequent
fertilization is random.
RrYy
Monohybrid Ratios Preserved
X
RrYy
Product Rule Predicts Combinations
¾ Round x ¾ Yellow =
315 round, yellow (~9/16)
¾ Round x ¼ Green =
108 round, green (~3/16)
¼ Wrinkled x ¾ Yellow =
101 wrinkled, yellow (~3/16)
¼ Wrinkled x ¼ Green =
32 wrinkled, green (~1/16)
F1: Round, Yellow: RrYy
Each gamete gets a gene
for each trait:
R or r
AND
Y or y
RY
Ry
rY
R = ½,
r=½
Y = ½,
y=½
So, if R’s and Y’s are
inherited independently,
THEN each combination
should occur ¼ of time.
ry
IF the genes for these
traits are allocated to
gametes independently
of one another, then
each F1 parent should
produce four types of
gametes, in equal
frequencies
c. His explanation: (including patterns of dominance)
Independent Assortment
occurs HERE
Independent Assortment
occurs HERE
c. His explanation: (including patterns of dominance)
Independent Assortment
occurs HERE
Round Yellow = 9/16
Independent Assortment
occurs HERE
c. His explanation: (including patterns of dominance)
Independent Assortment
occurs HERE
Round Yellow = 9/16
Round Green = 3/16
Independent Assortment
occurs HERE
c. His explanation: (including patterns of dominance)
Independent Assortment
occurs HERE
Round Yellow = 9/16
Round Green = 3/16
Wrinkled Yellow = 3/16
Independent Assortment
occurs HERE
c. His explanation: (including patterns of dominance)
Independent Assortment
occurs HERE
Round Yellow = 9/16
(3/4) x (3/4)
Round Green = 3/16
(3/4) x (1/4)
Wrinkled Yellow = 3/16
(1/4) x (3/4)
Wrinkled Green = 1/16
(1/4) x (1/4)
C. Mendel’s Experiments
1.
2.
3.
4.
Monohybrid Experiments
Monohybrid Test Cross
Dihybrid Experiments
Dihybrid Test Cross
The hypothesis rests on the gametes produced by the F1 individual.
How can we determine if they are produced in a 1 : 1 : 1 : 1 ratio?
¼ RY
¼ Ry
¼ rY
RrYy
¼ ry
C. Mendel’s Experiments
1.
2.
3.
4.
Monohybrid Experiments
Monohybrid Test Cross
Dihybrid Experiments
Dihybrid Test Cross
Cross with a recessive individual that
can only give recessive alleles for
both traits to all offspring
rryy
All gametes
= ry
RrYy
¼ RY
¼ RrYy
¼ Ry
¼ Rryy
¼ rY
¼ rrYy
¼ ry
¼ rryy
Genotypic
Frequencies
in offspring
C. Mendel’s Experiments
1.
2.
3.
4.
Monohybrid Experiments
Monohybrid Test Cross
Dihybrid Experiments
Dihybrid Test Cross
Cross with a recessive individual that
can only give recessive alleles for
both traits to all offspring
rryy
All gametes
= ry
¼ RY
RrYy
¼ RrYy
¼ RY
¼ Ry
¼ Rryy
¼ Ry
¼ rY
¼ rrYy
¼ rY
¼ ry
¼ rryy
¼ ry
Genotypic
Frequencies
in offspring
And the phenotypes
of the offspring
reflect the gametes
donated by the RrYy
parent.
C. Mendel’s Experiments
D. Summary
1) Hereditary information is unitary and ‘particulate’, not blending
2) First Principle – SEGREGATION: During gamete formation, the two
particles governing a trait separate and go into different gametes; subsequent
fertilization is random.
3) Second Principle – INDEPENDENT ASSORTMENT: The way genes
for one trait separate and go into gametes does not affect the way other
genes for other traits separate and go into gametes; so all gene combinations
in gametes occur as probability dictates. Subsequent fertilization is random.
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
- What is the probability of an offspring expressing Ab?
- How many genotypes are possible in the offspring?
- how many phenotypes are possible in the offspring?
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
Do the Punnett Squares for each gene separately:
For A:
For B:
A
a
A
AA
Aa
a
Aa
aa
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
Do the Punnett Squares for each gene separately:
For A:
For B:
A
a
A
AA
Aa
a
Aa
aa
b
b
B
Bb
Bb
b
bb
bb
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
Do the Punnett Squares for each gene separately:
For A:
For B:
A
a
A
AA
Aa
a
Aa
aa
b
b
B
Bb
Bb
b
bb
bb
Answer the question for each gene, then multiply:
P(Aa) = ½
x
P(bb) = ½
= 1/4
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
- What is the probability of an offspring expressing Ab?
For A:
For B:
A
a
A
AA
Aa
a
Aa
aa
b
b
B
Bb
Bb
b
bb
bb
Answer the question for each gene, then multiply:
P(A) = 3/4
x
P(b) =
½
= 3/8
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
- What is the probability of an offspring expressing Ab?
- How many genotypes are possible in the offspring?
For A:
For B:
A
a
A
AA
Aa
a
Aa
aa
b
b
B
Bb
Bb
b
bb
bb
Answer the question for each gene, then multiply:
(AA, Aa, aa) = 3
x
(Bb, bb) = 2
= 6
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
For Example:
AaBb x Aabb
- what is the probability of an Aabb offspring?
- What is the probability of an offspring expressing Ab?
- How many genotypes are possible in the offspring?
- how many phenotypes are possible in the offspring?
A
a
A
AA
Aa
a
Aa
aa
For A:
For B:
b
b
B
Bb
Bb
b
bb
bb
Answer the question for each gene, then multiply:
(A, a) = 2
x
(B, b) = 2
= 4
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
- how many types of gametes can each parent produce?
- What is the probability of an offspring expressing ABCD?
- How many genotypes are possible in the offspring?
- how many phenotypes are possible in the offspring?
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
- how many types of gametes can each parent produce?
For Female:
For Male:
Aa
Bb
Cc
dd
AA
Bb
cc
DD
A, a
B, b
C, c
d
A
B, b
c
D
2
2
2
1
1
2
1
1
2x2x2x1=8
1x2x1x1=2
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
- how many types of gametes can each parent produce?
- What is the probability of an offspring expressing ABCD?
At A:
At B:
A
A
A
AA
AA
a
Aa
Aa
P(A) = 1
x
At C:
At D:
c
D
B
b
B
BB
Bb
C
Cc
b
Bb
bb
c
cc
p(B) = ¾
x
p(C) = ½
d
x
Dd
p(D) = 1
= 3/8
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
- how many types of gametes can each parent produce?
- What is the probability of an offspring expressing ABCD?
- How many genotypes are possible in the offspring?
- how many phenotypes are possible in the offspring?
At A:
At B:
A
A
A
AA
AA
a
Aa
Aa
At C:
B
b
B
BB
Bb
C
Cc
b
Bb
bb
c
cc
At D:
c
D
d
Dd
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems:
(female) AaBbCcdd
x AABbccDD (male)
- how many types of gametes can each parent produce?
- What is the probability of an offspring expressing ABCD?
- How many genotypes are possible in the offspring? 2 x 3 x 2 x 1= 12
- how many phenotypes are possible in the offspring? 1 x 2 x 2 x 1 = 4
At A:
At B:
A
A
A
AA
AA
a
Aa
Aa
At C:
B
b
B
BB
Bb
C
Cc
b
Bb
bb
c
cc
At D:
c
D
d
Dd
E. The Power of Independent Assortment
1. If you can assume that the genes assort independently, then you
can calculate ‘single gene’ outcomes and multiply results together…
2. You can easily address more difficult multigene problems.
As you can see, IA produces lots of variation, because of the multiplicative
effect of combining genes from different loci together in gametes, and then
combining them together during fertilization… we’ll look at this again;
especially with respect to Darwin’s 3rd dilemma.
III. Mendel’s Contributions
F. Evolution after Rediscovering Mendel (1903)
SOURCES OF VARIATION
Independent
Assortment
AGENTS OF CHANGE
V
A
R
I
A
T
I
O
N
Natural Selection