Transcript Document

Today’s Plan
• Course logistics
• Mendelian segregation
ONLINE RESOURCES
 Course web page is live
http://dbs.umt.edu/courses/biol223
 “Online Learning Center” for Genetics text
http://www.mhhe.com/brooker
Instructions on first couple of pages
 Register your iClicker at iClicker.com
iClickers
• Get one, bring it to class, use it at least once.
• Register. If you registered your iClicker for
Biol221 or another class in Fall 2008, you do NOT
need to re-register. Otherwise, you do.
• Relax, use the clicker in class.
• Participation counts -- 50 pts will reflect iClicker
use throughout the semester.
**If you are having issues getting registered etc.,
come see me or call the iClicker help line.**
Course structure
Discussion sections (1 hour/week)
• NO MEETING THIS WEEK
• Next week, go to your preferred (enrolled) section.
• An opportunity to discuss lecture topics in more
depth and go over homework assignments.
• Participation counts -- a 5 pt. exercise will start
each session. See your TA beforehand if you need
to miss your usual section meeting.
Section
CRN
Time
Room TA
02
3 0 23 0
T 9 -1 0
NS 20 7
Lindy
03
3 0 23 1
T 1 1 -12
HS 4 1 1
Ellen
04
3 0 23 2
Th 9 -1 0
NS 20 7
Jon
05
3 0 23 3
W 1 1 -1 2
NS 30 7
Ellen
06
3 0 23 5
W 1 0 -1 1
HS 1 0 2
Lindy
07
3 0 23 6
W 1 1 -1 2
HS 1 0 2
Lindy
08
3 0 23 7
T 1 0 -11
LA 33 4
Lindy
09
3 0 23 8
T 1 0 -11
LA 20 1
Ellen
10
3 0 46 1
Th 10 -1 1
NS 20 7
Jon
11
3 0 46 2
Th 11 -1 2
HS 4 1 1
Jon
12
3 0 49 3
T 1 -2
LA 24 9
Ellen
13
3 0 49 4
Th 1 -2
ED 3 12
Jon
For next week
• Turn in your HW1
to your TA’s folder
at Monday’s lecture
• Go to your section
(some rooms have
changed, so check!)
Course structure
Weekly Homework Assignments
• Worth 10 pts. each (11 total, drop lowest 2)
• Handed out in lecture each Monday and posted
online.
• Due in lecture the following Monday or by
special arrangement with your TA by noon.
• Answers are posted at 12:00 noon on Mondays,
so no late assignments will be accepted.
Course structure
Exams
• 2 midterms (125 pts each)
• Comprehensive final (200 pts)
• Each exam will have a take-home component (a
more extended homework, basically) as well as
in-class portion
• In-class exams will be partly multiple choice and
partly short answer/problem solving
Course Structure - Grading
Midterms (250)
In-class exams (2)
Take-homes (2)
100 pts each 200 pts
25 pts each 50 pts
Discussion sections (150)
HWs (top 9 of 11)
Participation
10 pts each
5 pts each
Final Exam (200)
In-class exam
Take-home
90 pts
60 pts
175 pts
25 pts
iClicker Participation
50 pts
Total
650 pts
For more details on policies etc., see syllabus handout or course page.
Questions??
Today... Basic transmission genetics
Why do we study Mendel?
Mendel’s 1st law of segregation
Using Punnett squares to predict
genotypic and phenotypic ratios in
progeny
Why do we study Mendel?
Science is a process, not
a collection of
information.
We study Mendel in
order to understand the
process of science.
Gregor Mendel (1822-1884)
“Father” of Genetics
Observation
Children
resemble
their parents.
Question
Why?
Transmission Genetics
Since 8000 BC – Neolithic
farmers select plants and
animals with desirable traits—
the highest-yielding grain, the
sweetest fruit, or the fattest cow.
Transmission Genetics
400 BC – Greek philosopher Hippocrates proposes that
tiny particles from every part of the body of each parent
became blended, producing an individual with the
characteristics of both.
350 BC – Aristotle dismisses Hippocrates’ theory,
noting that children do not always resemble parents. But
Aristotle’s thinking about heredity still centers on a
mixing of “fluids” from each parent.
Blending inheritance
Plutarch (75 BC): “Drunkards beget drunkards”.
Frequency of alcoholism in adopted children:
Non-alcoholic biological-parents
5%
One alcoholic biological-parent
30%
Children of non-alcoholics
raised by alcoholic parents
5%
Based solely on these data, the tendency to become an
alcoholic is –
(a) Entirely genetic
(b) Entirely environmental.
(c) Both genetic and environmental.
Darwin’s model of (blending) inheritance
• Gemmules from parts of the body were passed
on to progeny through the bloodstream
• Francis Galton experiment in 1871: Blood
transfusions in rabbits did not alter the color
(black, gray, or white) of progeny.
• Not very satisfying…
Mendel’s motivation was to discover the
mechanisms of inheritance that were needed for
Darwin’s theory of evolution by natural selection.
Darwin’s near miss. . . 1866 letter to A. Wallace
"My dear Wallace... I do not think you understand what I
mean by the non-blending of certain varieties… I
crossed the Painted Lady and Purple sweetpeas, which
are very differently coloured varieties, and got, even
out of the same pod, both varieties perfect but none
intermediate. Something of this kind I should think must
occur at least with your butterflies & the three forms of
Lythrum; tho' these cases are in appearance so wonderful,
I do not know that they are really more so than every
female in the world producing distinct male and female
offspring...
Believe me, yours very sincerely Ch. Darwin"
Gregor Mendel
• Contemporary of Charles Darwin
• Paper published 1865; unnoticed until 1900
– The Origin of Species (1859)
• Major contributions
– Particulate nature of inheritance
– Three Principles
(1) Dominance
(2) Segregation
(3) Independent assortment
Why did Mendel succeed?
He asked the right question.
He used an appropriate scientific method.
He chose the right organism.
Right Question
Whoever surveys the work in this field will come to the
conviction that among the numerous experiments, not one has
been carried out to an extent or in a manner that would make
it possible to determine the number of different forms in
which hybrid progeny appear, permit classification of these
forms in each generation with certainty, and ascertain their
numerical interrelationships. It requires a good deal of
courage indeed to undertake such a far-reaching task;
however, this seems to be the one correct way of finally
reaching the solution to a question whose significance for the
evolutionary history of organic forms must not be
underestimated.
Gregor Mendel (1865)
Scientific Method
Observation
Hypothesis
Experimental Design
Quantitative analysis
Hypothesis testing
Scientific Method
Observation
Hypothesis
Experimental Design
Quantitative analysis
Hypothesis testing
Scientific Method
Mendel’s garden at
Brno monastery
Mendel’s notes on
Phaseolus (beans)
The right organism - garden peas (Pisum)
• Many seeds per cross
=> large sample sizes
• Short-generation time
• Easy to self-fertilize
and cross-fertilize
• Discrete traits
The right organism - garden peas (Pisum)
• Many seeds per cross
=> large sample sizes
• Short-generation time
• Easy to self-fertilize
and cross-fertilize
• Discrete traits
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
White
Remove stamens
from purple flower.
Parental
generation
Stamens
Transfer pollen from stamens
of white flower to the stigma of
a purple flower.
Purple
Cross-pollinated flower
forms seeds.
Plant seeds
from pod.
Firstgeneration
plants
The right organism - garden peas (Pisum)
• Many seeds per cross
=> large sample sizes
• Short-generation time
• Easy to self-fertilize
and cross-fertilize
• Discrete traits
TRAIT
VARIANTS
Purple
White
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Pod color
Green
Flower color
Flower position
Height
Tall
Yellow
Dwarf
Experimental approach
1. Generated ‘true-breeding’ lines for each trait
=> parental generation (P)
2. Crossed two different true-breeding lines
=> 1st generation progeny (F1 hybrids)
3. Self-fertilized an F1 hybrid
=> 2nd generation progeny (F2 hybrids)
Height
Tall
Dwarf
P plants
x
Tall
Dwarf
F1 seeds
F1 plants
Selffertilization
F2 seeds
F2 plants
Conclusions
P generation
Cross-fertilization
Tall “dominant”.
Dwarf “recessive”.
F1 generation
100% tall progeny (hybrids)
Self-fertilization
Recessive type still
present, hasn’t been
“blended” away.
F2 generation
787 tall
277 dwarf
PHENOTYPE
GENOTYPE
TT
P generation
tt
Cross-fertilization
F1 generation
100%
Tt
(tall)
100% tall progeny (hybrids)
Self-fertilization
25%
TT
F2 generation
75% tall
25% dwarf
50%
Tt
(tall)
25%
tt
(dwarf)
P plants
TT x tt
x
Tall
Dwarf
F1 seeds
All Tt
F1 plants
Selffertilization
Tt x Tt
F2 seeds
F2 plants
TT + 2 Tt + tt
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Female reproductive cells (F1)
Punnett
Square
Male reproductive cells (F1)
T
T
t
t
Female reproductive cells
Male reproductive cells
T
t
T
TT
Tt
t
Tt
tt
(TT + 2 Tt )+ tt = 3:1 ratio
Mendel’s Principles
1. Dominance: In a heterozygote, one allele may
conceal another.
2. Segregation: In a heterozygote, two different
alleles segregate from each other with equal
probability during the formation of gametes.
TRAIT
VARIANTS
Purple
White
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Pod color
Green
Flower color
Flower position
Height
Tall
Yellow
Dwarf
Repeated tests of model
P Cross
F1 generation
F2 generation
Ratio
Tall X
dwarf stem
All tall
787 tall,
277 dwarf
2.84:1
Round X
wrinkled seeds
All round
5,474 round,
1,850 wrinkled
2.96:1
Yellow X
Green seeds
All yellow
6,022 yellow,
2,001 green
3.01:1
Purple X
white flowers
All purple
705 purple,
224 white
3.15:1
Axial X
terminal flowers
All axial
651 axial,
207 terminal
3.14:1
Smooth X
constricted pods
All smooth
882 smooth,
229 constricted
2.95:1
Green X
yellow pods
All green
428 green,
152 yellow
2.82:1
In whippets, the “bully” trait is caused by a
recessive allele (b) at a single locus. You cross a
“bully” female with a heterozygous male. What
proportion of the resulting offspring would
you expect to be bullies?
(a) None.
(b) 25%
(c) 50%
(d) 75%
(e) 100%
Normal
Bully
Heterozygous male (Bb)
Bully female
(bb)
B
b
b
Bb
bb
b
Bb
bb
(c) 50% bully (bb)
Key Terms
P = parental generation
homozygous
F1, F2, Fn generations
heterozygous
phenotype, trait
dominant
genotype
recessive
gene
locus (plural: loci)
allele
Mendels’ reasoning in modern terms
1. Each parent carries 2 “factors” (alleles) for a trait
2. The two alleles can be identical or different
(true-breeding parents have 2 identical alleles and are
termed homozygous)
3. When 2 alleles are different (individual is
heterozygous) , one may dominant (determines the
trait) and the other recessive (hidden)
4. Alleles segregate equally (50:50) and gametes fuse at
random => Mendel’s 1st law of segregation
Friday: Independent Assortment
Course structure
Question/Answer Sessions
• Begin NEXT week
• Thursdays 6:00-7:30 pm HS411
• Not a review, but an extra opportunity for you to
ask questions about the lectures, reading or
homework problems
• Also my office hours:
9-11 MWF in HS309A and by appt.
Scientific Method
Whoever surveys the work in this field will come to the
conviction that among the numerous experiments, not one has
been carried out to an extent or in a manner that would make
it possible to determine the number of different forms in
which hybrid progeny appear, permit classification of these
forms in each generation with certainty, and ascertain their
numerical interrelationships. It requires a good deal of
courage indeed to undertake such a far-reaching task;
however, this seems to be the one correct way of finally
reaching the solution to a question whose significance for the
evolutionary history of organic forms must not, be
underestimated.
Gregor Mendel (1865)