BIO 221: GENETICS

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BIO 221 GENETICS
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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
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II. Darwins 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
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• II. Darwins Contributions
• B. His Theories
• Evolution proper species change
• Evidence

a. Change in domesticated animals and plants
over time
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• II. Darwins Contributions
• B. His Theories
• Evolution proper species change
• Evidence

b. Changes in lineages in the fossil record
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• II. Darwins Contributions
• B. His Theories
• 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
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• II. Darwins Contributions
• B. His Theories
• Common Ancestry Species are related by
  descent and have diverged from one another
• Evidence

Homologous Structures
Vestigial Structures
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• II. Darwins Contributions
• B. His Theories
• Common Ancestry Species are related by
  descent and have diverged from one another
• Evidence

Whale embryo w/leg buds
Embryology
photo
Haeckel
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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
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II. Darwins 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.
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II. Darwins 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)
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II. Darwins 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)
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II. Darwins 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.
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II. Darwins Contributions B. His Theories 3.
Natural Selection HOW species change
Evidence 3. Convergence in traits for organisms
experiencing the same environment.
Australia (Marsupials)
South America (Placentals)
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II. Darwins 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.
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II. Darwins 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).
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II. Darwins 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
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II. Darwins 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).
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II. Darwins Contributions C. His Dilemmas 1.
The evolution of complex structures
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Dawkins Evolution of the Camera Eye
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II. Darwins 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)
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II. Darwins Contributions C. His Dilemmas 2.
The lack of intermediates
?
X
X
X
?
X
X
X
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II. Darwins 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)
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II. Darwins Contributions C. His Dilemmas 2.
The lack of intermediates
X
Better adapted descendant outcompetes ancestral
type
X
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II. Darwins Contributions C. His Dilemmas 2.
The lack of intermediates
X
X
Better adapted descendant outcompetes ancestral
type
X
X
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II. Darwins Contributions C. His Dilemmas 2.
The lack of intermediates
X
X
X
Better adapted descendant outcompetes ancestral
type
X
X
X
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II. Darwins Contributions C. His Dilemmas 2.
The lack of intermediates
I believe the answer mainly lies in the record
being incomparably less perfect than is generally
supposed. The Origin of Species (Darwin 1859)
?
X
X
X
X
X
X
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II. Darwins 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)
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II. Darwins Contributions C. His Dilemmas 3.
What is the source of heritable variation?
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II. Darwins 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)
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"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).
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II. Darwins Contributions D. Darwins Model of
Evolution 3. What is the source of heritable
variation?
SOURCES OF VARIATION AGENTS OF CHANGE
Natural Selection
?
V A R I A T I O N
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Modern Biology I. Overview II. Darwins
Contributions III. Mendel's Contributions
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III. Mendel's Contributions A. Mendels Life -
Born July 20, 1822 in Czech Rep. - Entered
Augustinian Abbey in Brno 1843
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III. Mendel's Contributions A. Mendels 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.
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III. Mendel's Contributions A. Mendels Life B.
Pre-Mendelian Ideas About Heredity
Traits run in families.
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III. Mendel's Contributions A. Mendels Life B.
Pre-Mendelian Ideas About Heredity 1.
Preformationist Ideas
OVIST
HOMUNCULAN
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III. Mendel's Contributions A. Mendels Life B.
Pre-Mendelian Ideas About Heredity 1.
Preformationist Ideas 2. Epigenetic Ideas
?
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• III. Mendel's Contributions
• A. Mendels Life
• B. Pre-Mendelian Ideas About Heredity
• 1. Preformationist Ideas
• Epigenetic Ideas
• Blending Heredity

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III. Mendel's Contributions A. Mendels Life B.
Pre-Mendelian Ideas About Heredity C. Mendels
Experiments
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C. Mendels Experiments 1. Monohybrid Experiments
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C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses
Pollen (purple) Ovule (white)
Ovule (purple) Pollen (white)
WHY??
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C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses
Results falsified both the ovist and homunculan
schools hereditary information must come from
both parents.
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C. Mendels 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 31 ratio of purple to white.
(705224) SO, the F1 Purple flowered plant had
particles for white that were not expressed, but
could be passed on.
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- Proposed 4 postulates (hypotheses) to explain
his data 1) hereditary material is
particulate
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- Proposed 4 postulates (hypotheses) to explain
his data 1) hereditary material is
particulate. and each organism has 2 particles
governing each trait
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- 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).
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- 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
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- 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 parentand
vice-versa). This is Mendels Principle of
Segregation
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C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
Mendels ideas rested on the hypothesis that the
F1 plants were hiding a gene for
white Hypothesized Genotype Ww
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C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
½ W
Based on his hypotheses (postulates), the plant
should produce two types of gametes at equal
frequency.
Ww
½ w
Mendels 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?
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Mate with the recessive parent, which can only
give recessive alleles to offspring
C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
ww
w
½ W
Ww
½ w
Mendels ideas rested on the hypothesis that the
F1 plants were hiding a gene for
white Hypothesized Genotype Ww
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Mate with the recessive parent, which can only
give recessive alleles to offspring
C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
ww
w
½ W
½ Ww
½ ww
Ww
½ w
Mendels ideas rested on the hypothesis that the
F1 plants were hiding a gene for
white Hypothesized Genotype Ww
Genotypic Ratio of offspring
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Mate with the recessive parent, which can only
give recessive alleles to offspring
C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
ww
w
½ W
½ Ww
½ ww
½ W
½ w
Ww
½ w
Mendels 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
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Mate with the recessive parent, which can only
give recessive alleles to offspring
C. Mendels Experiments 1. Monohybrid
Experiments a. reciprocal crosses b. crossing
the F1 hybrids c. Proposed four postulates 2.
Monohybrid Test Cross
ww
Same as gamete frequencies of unknown parent
w
½ W
½ Ww
½ ww
½ W
½ w
Ww
½ w
Mendels 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
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C. Mendels Experiments 1. Monohybrid
Experiments 2. Monohybrid Test Cross 3.
Dihybrid Experiments a. Parental cross
Round and Yellow Peas Wrinkled and Green Peas
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C. Mendels 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
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C. Mendels 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)
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C. Mendels 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)
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101 wrinkled, yellow (3/16)
133 wrinkled (1/4)
32 wrinkled,green(1/16)
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C. Mendels 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)
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101 wrinkled, yellow (3/16)
140 Green (1/4)
32 wrinkled, green (1/16)
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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.
C. Mendels Experiments 1. Monohybrid
Experiments 2. Monohybrid Test Cross 3.
Dihybrid Experiments a. Parental cross
b. F1 x F1 cross c. His explanation
X
RrYy
RrYy
Monohybrid Ratios Preserved
Product Rule Predicts Combinations
315 round, yellow (9/16)
¾ Round x ¾ Yellow
108 round, green (3/16)
¾ Round x ¼ Green
101 wrinkled, yellow (3/16)
¼ Wrinkled x ¾ Yellow
32 wrinkled, green (1/16)
¼ Wrinkled x ¼ Green
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F1 Round, Yellow RrYy Each gamete gets a
gene for each trait R or r AND Y or
y RY Ry rY ry R ½, r ½ Y ½, y
½ So, if Rs and Ys are inherited
independently, THEN each combination should
occur ¼ of time.
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
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c. His explanation (including patterns of
dominance)
Independent Assortment occurs HERE
Independent Assortment occurs HERE
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c. His explanation (including patterns of
dominance)
Independent Assortment occurs HERE
Round Yellow 9/16
Independent Assortment occurs HERE
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c. His explanation (including patterns of
dominance)
Independent Assortment occurs HERE
Round Yellow 9/16 Round Green 3/16
Independent Assortment occurs HERE
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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
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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)
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C. Mendels Experiments 1. Monohybrid
Experiments 2. Monohybrid Test Cross 3.
Dihybrid Experiments 4. 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
¼ ry
RrYy
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Cross with a recessive individual that can only
give recessive alleles for both traits to all
offspring
C. Mendels Experiments 1. Monohybrid
Experiments 2. Monohybrid Test Cross 3.
Dihybrid Experiments 4. Dihybrid Test Cross
rryy
All gametes ry
¼ RY
¼ Ry
¼ rY
¼ ry
¼ RrYy
¼ Rryy
¼ rrYy
¼ rryy
RrYy
Genotypic Frequencies in offspring
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Cross with a recessive individual that can only
give recessive alleles for both traits to all
offspring
C. Mendels Experiments 1. Monohybrid
Experiments 2. Monohybrid Test Cross 3.
Dihybrid Experiments 4. Dihybrid Test Cross
rryy
All gametes ry
¼ RY
¼ Ry
¼ rY
¼ ry
¼ RrYy
¼ Rryy
¼ rrYy
¼ rryy
¼ RY
¼ Ry
¼ rY
¼ ry
And the phenotypes of the offspring reflect the
gametes donated by the RrYy parent.
RrYy
Genotypic Frequencies in offspring
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C. Mendels 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.
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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?
73
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
74
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
75
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 Answer the
question for each gene, then multiply P(Aa) ½
x P(bb) ½ 1/4
A a
A AA Aa
a Aa aa
b b
B Bb Bb
b bb bb
76
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 Answer the question for each gene, then
multiply P(A) 3/4 x P(b) ½
3/8
A a
A AA Aa
a Aa aa
b b
B Bb Bb
b bb bb
77
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 Answer the question for each gene,
then multiply (AA, Aa, aa) 3 x (Bb,
bb) 2 6
A a
A AA Aa
a Aa aa
b b
B Bb Bb
b bb bb
78
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? For A
For B Answer the question for
each gene, then multiply (A, a) 2
x (B, b) 2 4
A a
A AA Aa
a Aa aa
b b
B Bb Bb
b bb bb
79
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)
80
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?
81
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 2 x 2
x 2 x 1 8 1 x 2 x 1 x 1 2
Aa Bb Cc dd
A, a B, b C, c d
2 2 2 1
AA Bb cc DD
A B, b c D
1 2 1 1
82
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 At
C At D P(A) 1 x p(B) ¾
x p(C) ½ x p(D) 1 3/8
A A
A AA AA
a Aa Aa
B b
B BB Bb
b Bb bb
c
C Cc
c cc
D
d Dd
83
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 At C At D
A A
A AA AA
a Aa Aa
B b
B BB Bb
b Bb bb
c
C Cc
c cc
D
d Dd
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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 At
C At D
A A
A AA AA
a Aa Aa
B b
B BB Bb
b Bb bb
c
C Cc
c cc
D
d Dd
85
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 well look at this again
especially with respect to Darwins 3rd dilemma.
86
III. Mendels Contributions F. Evolution after
Rediscovering Mendel (1903)
SOURCES OF VARIATION AGENTS OF CHANGE
Natural Selection
V A R I A T I O N
Independent Assortment