Download Punnet squares lecture rev 1-27

http://fi.wikipedia.org/wiki/Gregor_Mendel
http://www.personal.psu.edu/staff/d/c/dcw1/graphics/pea_plant.jpg
Father of Modern Genetics
•The first person to trace the characteristics of successive generations of a living
thing
•He was not a world-renowned scientist of his day.
• Rather, he was an Augustinian monk who taught natural science to high school
students.
• Second child of Anton and Rosine Mendel
• They were farmers in Brunn
• They couldn’t afford for him to attend college
• Gregor Mendel then attended the Augustinian
Monastery and became a monk
Where Mendel Studied
• He was later sent to the University of Vienna to study. By both his professors
at University and his colleagues at the monastery, Mendel was inspired to
study variance in plants
The Monastery Garden with the greenhouse which
Gregor J. Mendel, O.S.A., had built in 1870. Its appearance
before 1902.Courtesy of Villanova University Archives.
Gregor J. Mendel, O.S.A., experimental garden (35x7
meters) in the grounds of the Augustinian Monastery in
Old Brno.Its appearance before 1922. Courtesy of
Villanova University Archives.
How Mendel Got Started
• Mendel's attraction to research was based on his
love of nature.
• He was not only interested in plants, but also in
meteorology and theories of evolution.
• Mendel often wondered how plants obtained
atypical characteristics.
Gregor Mendel
(1822-1884)
Responsible
for the Laws
governing
Inheritance of
Traits
copyright cmassengale
7
Site of
Gregor
Mendel’s
experimental
garden in the
Czech
Republic
copyright cmassengale
8
The Birth of the idea: Heredity
• On a walk around the monastery, he found an atypical variety
of an ornamental plant.
• He took it and planted it next to the typical variety.
• He grew their progeny side by side to see if there would be
any approximation of the traits passed on to the next
generation.
• This experiment was "designed to support or to illustrate
Lamarck's views concerning the influence of environment
upon plants.“
• He found that the plants' respective offspring retained the
essential traits of the parents, and therefore were not
influenced by the environment.
Mendel's research reflected his
personality.
 Once he crossed peas and
mice of different varieties
"for the fun of the thing,"
and the phenomena of
dominance and segregation
"forced themselves upon
notice."
 He saw that the traits were
inherited in certain
numerical ratios.
 He then came up with the
idea of dominance and
segregation of genes and set
out to test it in peas.
 It took seven years to cross
and score the plants to the
thousand to prove the laws
of inheritance!
Mendel's work became the
foundation for modern genetics.
• The impact of genetic theory is no longer questioned in
anyone's mind.
• Many diseases are known to be inherited
• and pedigrees are typically traced to determine the
probability of passing along an hereditary disease.
• Plants are now designed in laboratories to exhibit
desired characteristics.
• The practical results of Mendel's research has not only
changed the way we perceive the world, but also the way
we live in it.
• Took seven years to prove laws of
inheritance
• -Basic Laws• Heredity Factors do not combine
• Each member of a parental generation
transfers only one half of its heredity factors
to each offspring
• Mendel’s works became the foundation of modern
genetics
• Later crossed mice and pea plants
• Noticed traits were inherited in certain numerical ratios
• Came up with idea of dominance and segregation of
genes and set out to test it in peas
• Love of nature encouraged his interest in research
• Also interested in meteorology and theories of
evolution
http://www.fort.usgs.gov/resources/spotlight/prairiedogs/images/people.gif
Genetics
• Is the study of heredity
• Heredity: the transmission of traits
from one generation to the next
http://www.ogdenfinancial.com/images/three%20generations%202.jpg
Its all in our genes
• You have already learned about
chromosomes as compact carriers of
DNA.
http://www.ogm-info.com/chromosome(color).jpg
http://employees.csbsju.edu/hjakubowski/classes/ch331/dna/chr
omosomes2.gif
Gene
• “A discrete unit of hereditary information
consisting of a specific nucleic sequence
in DNA (or RNA in some viruses)”
• -Campbell Biology
• Locus: a gene’s specific location on a
chromosome ( the plural is loci)
• Homologous Chromosomes: alike
chromosomes carrying genes for the
same heritable characteristics
Homologous Chromosomes
http://library.thinkquest.org/C0118084/Gene/Genetic_variation/dominant_reces
sive_files/homologous_chromosomes.gif
• Allele: an alternate form of a gene
• Ie. One coding for blue eyes and one for
brown
Allele
Allele
Centromere
• The joining point of 2 sister chromatids
• telomere: the protective structure at the
end of the chromosome (protects DNA
when it is copied)
Sister chromatids
• Replicated forms of a chromosome jointed
together by the centromere and eventually
separated by mitosis or meiosis 2
(Don’t worry we’ll be learning about mitosis
and meiosis on Monday)
Parts of a Chromosome
http://genetics.gsk.com/graphics/chromosome.gif
• Character: a feature that can be
inherited by offspring from a parent
(i.e. blue eyes)
http://sheilasspot.blogspot.com/uploaded_images/Blue%20eyes-750090.jpg
• Trait: a variation of a character
I.e. blue or green brown eyes are traits
http://www.absolutestockphoto.com/albums/userpics/10007/normal_Absolute_7_5469.jpg
What Mendel did
• He took true
breeding pea
plants
• Meaning the
parents only
produced offspring
with the same
combination of
traits that they had.
http://mac122.icu.ac.jp/gen-ed/mendel-gifs/02-pea-life-cycle.JPG
The parents possessed a
combination of traits below
http://www.gwu.edu/~darwin/BiSc150/One/peas.gif
For now we will examine one trait
set at a time
• This is called monohybridization or a
monohybrid cross
• The crossing of a single trait
• The parents generation is the P generation
• The first generation of offspring is the F1
generation
• The second generation of offspring is the
F2 generation
http://fig.cox.miami.edu/~cmallery/150/mendel/c14x2flower-color.jpg
• The following is adapted from:
http://www.borg.com/~lubehawk/mendel.ht
m#Law%202%20Seg
• 1. the Law of Dominance
2. the Law of Segregation
3. the Law of Independent Assortment
The Law of Dominance
• “In a cross of parents that are pure for
contrasting traits, only one form of the
trait will appear in the next
generation. Offspring that are hybrid
for a trait will have only the dominant
trait in the phenotype.”
• A dominant trait will mask or cover up a
recessive trait
• A recessive trait is only seen if the
offspring receive a copy of it from each
parent
• Dominant DOES NOT = better
http://www.thefunnypage.com/toes/
• A Dominant trait is expressed as a capital
letter i.e. A
• A Recessive trait is expressed as a
lowercase letter i.e. a
The Law of Segregation
“During the formation of gametes (eggs
or sperm), the two alleles responsible
for a trait separate from each
other. Alleles for a trait are then
"recombined" at fertilization,
producing the genotype for the traits of
the offspring. “
(more about this on Monday)
The Law of Independent
Assortment
“Alleles for different traits are distributed
to sex cells (& offspring) independently
of one another.”
In other words the traits can be in any
combinations in offspring it doesn't have to
be all from the mother or all from the
father.
Sweet picture I found on the
internet
• Homozygous : having identical
alleles for the same character “AA or
aa”
• Heterozygous: having 2 different
alleles for the same character “Aa”
Genotype: what the genetic code of
the organism is
Phenotype: what is actually
expressed (seen)
• Expressed traits: the phenotype what is
seen
How do we do this?
http://www.fathom.com/feature/122612/mendel.jpg
Parents Tt & tt
http://www.borg.com/~lubehawk/psquare.htm
http://www.borg.com/~lubehawk/psquare.htm
http://www.borg.com/~lubehawk/psquare.htm
http://www.borg.com/~lubehawk/psquare.htm
Answer
http://www.borg.com/~lubehawk/psquare.htm
Try this one
http://www.borg.com/~lubehawk/psquare.htm
Now try this
Answer
One step further comparing two
traits at once
• dihybrid cross: comparing two traits
simultaneously
YYRR
yyrr
http://www.micro.utexas.edu/courses/levin/bio304/genetics/dihybridcross.comp.gif
http://www.nap.edu/openbook/0309092051/html/images/p2000b08fg75001.jpg
How to figure out the number
square in your punnet square
n
4
N- number of traits
http://fig.cox.miami.edu/~cmallery/150/mendel/dihybrid.htm
F1
generation
Dihybrid Cross
RY
Ry
rY
ry
RY
Ry
rY
ry
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Dihybrid Cross
RY
RY RRYY
Ry RRYy
rY RrYY
ry
RrYy
Ry
rY
ry
RRYy
RrYY
RrYy
RRyy
RrYy
Rryy
RrYy
rrYY
rrYy
Rryy
rrYy
rryy
copyright cmassengale
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
ratio
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Dihybrid Cross
Round/Yellow: 9
Round/green:
3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1
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Practice
•
•
Construct a Punnett Square for each of
the following crosses.
Write the Genotypic and Phenotypic
Ratio below the Punnett Squares.
1. SsTt X SsTt
2. SSTt X SsTt
3. SSTT X SsTt
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
st
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
ST
St
sT
st
St
sT
st
S = striped
s = plain
T = tail
t = no tail
SsTt X SsTt
ST
St
sT
st
ST
SSTT SSTt SsTT SsTt
St
SSTt SStt
SsTt
sT
SsTT SsTt
ssTT ssTt
st
SsTt
ssTt
Sstt
S = striped
s = plain
T = tail
t = no tail
Sstt
sstt
Genotypes: 1 SSTT: 2 SSTt: 1 SStt: 2 SsTT: 4 SsTt: 2 Sstt: 1 ssTT: 2 ssTt: 1 sstt
Phenotypes: 9 striped, tail : 3 striped, no tail : 3 plain, tail : 1 plain, no tail
SSTt X SsTt
ST
St
sT
st
ST
SSTT SSTt SsTT SsTt
St
SSTt SStt
SsTt
Sstt
ST
Same as
above
Same as
above
Same as
above
Same as
above
St
Same as
above
Same as
above
Same as
above
Same as
above
S = striped
s = plain
T = tail
t = no tail
If they are the same
as above you do
NOT have to
rewrite the
genotype
Genotypes: 1 SSTT: 1SSTt: 1SsTT: 1SsTt: 1SSTt: 1SStt: 1SsTt: 1Sstt
Phenotypes: 6 Striped with Tail: 2 Striped with no tail (3:1 reduced)
SSTT X SsTt
ST
Same
ST
St
sT
st
SSTT SSTt SsTT SsTt
ST
ST
ST
Genotypes: 1 SSTT: 1 SSTt: 1 SsTT: 1 SsTt
Phenotypes: 4 Striped Tail (100%)
S = striped
s = plain
T = tail
t = no tail
Test Cross
• A mating between an individual of unknown
genotype and a homozygous recessive
individual.
• Example: bbC__ x bbcc
•
•
•
•
•
•
BB = brown eyes
Bb = brown eyes
bb = blue eyes
bC
CC = curly hair
Cc = curly hair
cc = straight hair
b___
bc
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Test Cross
• Possible results:
bc
bC
b___
C
bbCc
bbCc
or
copyright cmassengale
bc
bC
b___
c
bbCc
bbcc
82
Summary of Mendel’s laws
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall
25% short
RrGg x RrGg
round & green
x
round & green
9/16
pods
3/16
pods
3/16
pods
1/16
pods
copyright cmassengale
round seeds & green
round seeds & yellow
wrinkled seeds & green
wrinkled seeds & yellow
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Incomplete Dominance
and
Codominance
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• Incomplete dominance- a blending of
characters. No dominant or recessive
Incomplete Dominance
• F1 hybrids have an appearance somewhat
in between the phenotypes of the two
parental varieties.
• Example: snapdragons (flower)
• red (RR) x white (rr)
r
r
•
•
RR = red flowerR
rr = white flower
R
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Incomplete Dominance
r
r
R Rr
Rr
R Rr
Rr
produces the
F1 generation
All Rr = pink
(heterozygous pink)
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If you cross the F1 generation, what
kind of offspring do you get?
r
r
R Rr
Rr
R Rr
Rr
R
R RR
r
Rr
r
Rr
rr
Incomplete Dominance
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Codominance
• Two alleles are expressed (multiple
alleles) in heterozygous individuals.
• Example: blood type
•
•
•
•
1.
2.
3.
4.
type A
type B
type AB
type O
=
=
=
=
IAIA or IAi
IBIB or IBi
IAIB
ii
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Codominance Problem
• Example:
(IBIB)
•
homozygous male Type B
x
heterozygous female Type A
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
(IAi)
copyright cmassengale
1/2 = IAIB
1/2 = IBi
92
Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
copyright cmassengale
1/2 = IAi
1/2 = IBi
93
Codominance
• Question:
If a boy has a blood type O and
his sister has blood type AB,
what are the genotypes and
phenotypes of their
parents?
• boy - type O (ii) X girl - type AB
(IAIB)
copyright cmassengale
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Codominance
• Answer:
IA
IB
i
i
IAIB
ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
copyright cmassengale
95
What determines if you are male or
female???
• Females have 2 “X” chromosomes.
• Males have 1 “X” and 1 “y” chromosome.
• “Y” chromosome is very small and carries
few traits
X
X
Female
X
y
Male
Sex-linked Traits
• Traits (genes) located on the sex
chromosomes
• Sex chromosomes are X and Y
• XX genotype for females
• XY genotype for males
• Many sex-linked traits carried on
X chromosome
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Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
copyright cmassengale
Xy chromosome - male
98
Sex-linked Trait Problem
• Example: Eye color in fruit flies
•
(red-eyed male) x (white-eyed female)
XR Y
x
XrXr
• Remember: the Y chromosome in males
does not carry traits.
• RR = red eyed
Xr
Xr
• Rr = red eyed
• rr = white eyed
• XY = male
XR
• XX = female
Y
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Sex-linked Trait Solution:
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
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100
Female Carriers
copyright cmassengale
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Genetic Practice
Problems
copyright cmassengale
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Breed the P1 generation
• tall (TT) x dwarf (tt) pea plants
t
t
T
T
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Solution:
tall (TT) vs. dwarf (tt) pea plants
t
t
T
Tt
Tt
produces the
F1 generation
T
Tt
Tt
All Tt = tall
(heterozygous tall)
copyright cmassengale
104
Breed the F1 generation
• tall (Tt) vs. tall (Tt) pea plants
T
t
T
t
copyright cmassengale
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Solution:
tall (Tt) x tall (Tt) pea plants
T
t
T
TT
Tt
t
Tt
tt
produces the
F2 generation
1/4 (25%) = TT
1/2 (50%) = Tt
1/4 (25%) = tt
1:2:1 genotype
3:1 phenotype
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Good site for help
http://biology.clc.uc.edu/courses/bio105/ge
neprob.htm
http://homepages.ius.edu/GKIRCHNE/Men
del.htm
Try these
Percentages
Practice
Hardy-Weinberg
• Taken from
http://anthro.palomar.edu/synthetic/synth_
2.htm
• “This definition of evolution was developed
largely as a result of independent work in the
early 20th century by Godfrey Hardy, an
English mathematician, and Wilhelm Weinberg,
a German physician. Through mathematical
modeling based on probability, they concluded
in 1908 that gene pool frequencies are
inherently stable but that evolution should be
expected in all populations virtually all of the
time. They resolved this apparent paradox by
analyzing the net effects of potential evolutionary
mechanisms. “
• They originally wrote it in a restaurant ton
a napkin after a conversation about the
topic.
• Don’t you wish you were that smart
The 7 conditions need to use the
equation
•
•
•
•
•
•
1. mutation is not occurring
2. natural selection is not occurring
3. the population is infinitely large
4. all members of the population breed
5. all mating is totally random
6. everyone produces the same number
of offspring
• 7. there is no migration in or out of the
population
• “used to discover the probable genotype
frequencies in a population and to track
their changes from one generation to
another “
Hardy-Weinberg equilibrium
equation
What the letter mean
• p is defined as the frequency of the
dominant allele
• q as the frequency of the recessive allele
• p² is the predicted frequency of
homozygous dominant (AA)
• 2pq is the predicted frequency of
heterozygous (Aa)
• q² is the predicted frequency of
homozygous recessive (aa)
• Those who express the trait in their
phenotype could be either homozygous
dominant (p²) or heterozygous (2pq).
• The dominant phenotype is p = 1 - q
• The recessive phenotype is q
• Albinism is a rare genetically
inherited trait that is only expressed
in the phenotype of homozygous
recessive individuals (aa). The
average human frequency of albinism
in North America is only about 1 in
20,000.
http://media-cyber.law.harvard.edu/blogs/static/dowbrigade/sadd.jpg
• Referring back to the Hardy-Weinberg
equation (p² + 2pq + q² = 1), the frequency
of homozygous recessive individuals (aa)
in a population is q². Therefore, in North
America the following must be true for
albinism:
• q² = 1/20,000 = .00005
• By taking the square root of both sides of
this equation, we get: (Note: the
numbers in this example are rounded off
for simplification.)
• q = .007
• In other words, the frequency of the recessive
albinism allele (a) is .00707 or about 1 in
140. Knowing one of the two variables (q) in the
Hardy-Weinberg equation, it is easy to solve for
the other (p).
• p = 1 - qp = 1 - .007p = .993
• The frequency of the dominant, normal allele (A)
is, therefore, .99293 or about 99 in 100.
• The next step is to plug the
frequencies of p and q into the HardyWeinberg equation:
• p² + 2pq + q² = 1
• (.993)² + 2 (.993)(.007) + (.007)² = 1
• .986 + .014 + .00005 = 1
This gives us the frequencies for
each of the three genotypes for this
trait
in
the
population:
• p² =
predicted frequency
of homozygous
dominant individuals = .986 = 98.6%
• 2pq =
predicted frequency
of heterozygous
individuals = .014 = 1.4%
• q² =
predicted frequency
of homozygous
recessive individuals
(the albinos)
• With a frequency of .005% (about 1 in 20,000),
albinos are extremely rare. However,
heterozygous carriers for this trait, with a
predicted frequency of 1.4% (about 1 in 72), are
far more common than most people
imagine. There are roughly 278 times more
carriers than albinos. Clearly, though, the vast
majority of humans (98.6%) probably are
homozygous dominant and do not have the
albinism allele. why?
http://www.anselm.edu/homepage/jpitocch/genbios/23-03a-HardyWeinberg-L.gif
• expressed, homozygous, heterozygous,
monohybrid cross, dihybrid cross,
plieotrophy, complete dominance, multiple
alleles, hardy-weinberg, ratios ecological
effect p435
Sites for practice
• http://www.changbioscience.com/genetics/
punnett.html
• http://science.nhmccd.edu/biol/dihybrid/dih
ybrid.html
• http://www.athro.com/evo/gen/punexam.ht
ml#monohybrid