gregor mendel gregor mendel: –austrian monk lived from 1822-1884 –mendel developed principles of...
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Gregor Mendel• Gregor Mendel:
– Austrian monk lived from 1822-1884
– Mendel developed principles of heredity without any knowledge of genes or chromosomes
– His principles were established through experiments with pea plants
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Why was Mendel successful with the pea?
• Used pure breeding, 7 contrasting traits• Studied characteristics one at a time for many
generations• Used mathematics in analyzing his results• Obtained large numbers of offspring• Chose pea plants which normally self-fertilize• Inexpensive • Used scientific method • Easy to pollinate (transfer of male pollen to egg)
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Mendel’s 7 contrasting traits
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Genetics Terms• Define genes:
factors that control organism’s traits.
the part of chromosome that contains the genetic code.
• Every organism requires a set of coded instructions for specifying its traits
• For offspring to resemble their parents, their must be a reliable way to transfer hereditary information from one generation to the next
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Genetics Terms• homozygous (pure): the alleles on homologous
chromosomes are the same • heterozygous: (hybrid): the alleles on
homologous chromosomes are different • parental generation (P): the two original
organisms being crossed - usually pure
• first filial generation (F1) : the first generation of offspring from the parents
• second filial generation (F2) : generation of offspring arising from the first filial generation
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Genetics Terms
• Genotype: the genetic makeup of an organism– Homozygous Dominant: TT– Homozygous Recessive: tt– Heterozygous: Tt
• Phenotype: the appearance of an organism– Describes what it looks like
TT - Tall tt - short Tt - Tall
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Punnett Squares• a model used to predict the results of a
genetic cross
• BB X bb
b
b
BB
B B
BB b
b b
b
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Three Laws by Mendel1. Law of Dominance: a pattern of heredity
in which one allele of a gene may express itself by masking the presence of the other allele
Dominant Trait: the trait or allele that is expressed (capital letter) R
Recessive Trait: the trait or allele that is present but that is not expressed (lowercase letter) r
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Three Laws by Mendel
1. Law of Dominance:
Example:red flower (RR) X white flower (rr) red flower (Rr)
X
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Example of Dominance
• R = red
• r = white
• RR x rr
R R
r
r
Rr
Rr
Rr Rr
Results:Phenotype:
Genotype:
Problem:Cross homozygous dominant with homozygous recessive
100% red
100% heterozygous
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2. Law of Segregation Mendel’s second law
– When gametes are formed during meiosis:• There is a random segregation of homologous
chromosomes
• Random segregation of sister chromatids & alleles
• The result: new gene combinations are likely to be produced
• Segregation means separation and can lead to genetic recombination.
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Phenotype:
____% red, ____% white
___ red : ___ white Genotype: ___% homozygous dominant, ___% homozygous recessive, ___% heterozygous
Example of Segregation
• R = red
• r = white
• Rr x Rr
R r
R
r
RR Rr
Rr rr
Problem:Cross two offspring from 1st cross (2 heterozygous parents)
75 25
13
252550
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3. Law of Independent Assortment
Mendel’s third Law – Scenario: Two different traits located on two different
chromosomes
• They segregate randomly during meiosis
• May be inherited independently of each other
• The cross of two organisms heterozygous for a trait is known
as a dihybrid cross
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Law of Independent Assortment
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Dihybrid CrossProblem:Cross homozygous tall and homozygous wrinkled seeds with homozygous short and homozygous smooth seeds
T = tallt = short
Q = wrinkledq = smooth
What are the genotypes for these plants?
TTQQ x ttqq
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TTQQ x ttqq
TtQq
TtQq
TtQq
TtQq TtQq TtQq TtQq
TtQq
TtQq
TtQqTtQqTtQq
TtQq
TtQq TtQq
TtQq
Phenotype: 100% Tall & Wrinkled
TQ TQ TQ TQtq
tq
tq
tq
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Dihybrid Cross
• What is the phenotype from this cross?– 100% Tall and Wrinkled
• What is the genotype from this cross?– We don’t worry about genotype for dihybrid
crosses
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Complete the following Dihybrid cross
Step 1 - set up gamettes(sex cells)
(1 3, 1 4, 2 3, 2 4)
TtQq x TtQq
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Complete the following Dihybrid cross TtQq x TtQq T-Tall t-short Q-Wrinkled q-smooth
TTQQ
TTQq
TtQQ
TtQq Ttqq ttQq ttqq
ttQq
Ttqq
TtQqTtQQTTQq
TTqq
TtQq ttQQ
TtQq
TQ tQTq tq
TQ
Tq
tQ
tq
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What are the phenotypes for the above cross???
• - Tall & Wrinkled
• - Tall & smooth
• - Short & wrinkled
• - Short & smooth
9
3
3
1
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Incomplete Inheritance• Two examples of Incomplete Inheritance:
– Incomplete Dominance & Codominance
• Incomplete Dominance: – A case where one allele is partially dominant over the other
– Examples of Incomplete Dominance:
red snapdragons X white snapdragons pink snapdragons
cross between black and white Andulusian
fowl gives blue (gray) fowl
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Example of Incomplete Dominance Pink Snapdragons
X
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Results:Phenotype: ___% red, ___% pink, ___% white
Genotype: ___% homozygous dominant ___% heterozygous___% homozygous recessive
Example of Incomplete Dominance
• R = red
• r = white
• Rr x Rr
R r
R
r
RR Rr
Rr rr
Problem:Cross offspring from 1st cross (2 heterozygous parents)
5025 25
255025
Ratio ___ : ___ : ___1 2 1
Ratio ___ : ___ : ___1 2 1
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Intermediate Inheritance• Codominance: a case in which neither allele is
dominant over the other– Alleles have equal power
• Examples:– Cross between red and white short horned cattle gives
roan cattle
– Checkered black & white chicken
– Sickle-cell Anemia - a blood disease where RBCs are sickle shaped or half moon. Most common African.
– Heterozygous - half normal half sickle shape
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Roan Cattle
Red CattleX
White Cattle
Roan Cattle
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Results:Phenotype: ___% red, ___% red & white, ___% white
Genotype: ___% homozygous dominant ___% heterozygous___% homozygous recessive
Example of Codominance
• R = red
• r = white
• Rr x Rr
R r
R
r
RR Rr
Rr rr
Problem:Cross offspring from 1st cross (2 heterozygous parents)
5025 25
255025
Ratio ___ : ___ : ___1 2 1
Ratio ___ : ___ : ___1 2 1
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Problem 1
Homozygous dominant
Phenotype of tt -------------------------
Genotype of tt---------------------------
Phenotype of TT -----------------------
Genotype of TT-------------------------
Phenotype of pure dominant--------
Genotype of pure dominant---------
Phenotype of pure recessive--------Genotype of pure recessive---------
Short
Homozygous recessive
Tall
Tall
TT
Shorttt
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__ __ x __ __
X Y
X
X
XX XY
XX XY
Results:
Phenotype: 50% male, 50% female Phenotype ratio: 2 male : 2 female
Problem 2:A married couple want to know their chances of having girl
X Y X X
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Phenotype: ___% red, white ___%
Phenotypic Ratio: __ : ___
Genotype: ___% heterozygous
___% homozygous dominant
____% homozygous recessive
• R = red
• r = white
• __ __ x __ __
R r
R
r
RR Rr
Rr rr
Problem 3: Cross two
heterozygous parents
R r rR
75
25
502525
25
3 red 1 white
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Results:
Phenotype: ___% red, white ___%
Phenotype Ratio: __ : _ _ __ Genotype: ___% heterozygous
___% homozygous dominant ___% homozygous recessive
• R = red
• r = white
• __ __ x __ __
R R
R
r
RR RR
Rr Rr
Problem 4: Pure dominant crossed with hybrid
R R rR
100
50500
0
4 red 4 white
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Phenotype: ___% red, white ___%
Phenotypic Ratio: __ : ___ Genotype: ___% heterozygous
___% homozygous dominant ___ % homozygous recessive
• R = red
• r = white
• __ __ x __ __
r r
R
r
Rr Rr
rr rr
Problem 5: The male’s genotype is homozygous recessive. The female is phenotypically dominant but does carry the recessive allele.
r r rR
50
50 050
50
2 red 2 white
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Results:
Phenotype: ___% red, ___ % red and white, white ___%
Phenotypic Ratio: __ red : __ red and white : ___ white Genotype: ___% heterozygous
___% homozygous dominant ___ % homozygous recessive
• R = red
• r = white
• __ __ x __ __
R r
R
r
RR Rr
Rr rr
Cross two heterozygous parents
R r rR
25
50 2525
25
1 2
Problem 6: Law of Codominance
50
1
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Results:
Phenotype: ___% red, ___ % pink, white ___%
Phenotype Ratio: __ red : __ pink : ___ white Genotype: ___% heterozygous
___% homozygous dominant ___ % homozygous recessive
• R = red
• r = white
• __ __ x __ __
R r
R
r
RR Rr
Rr rr
Cross two heterozygous parents
R r rR
25
502525
50
1 2
Problem 7: Law of Incomplete Dom
25
1
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Test Cross:
It will determine if a horse/dog in question is pure or carrying a recessive gene.
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• B = brown
• b = white
__ __ x __ __
or
__ __ x __ __
B B
b
b
Bb Bb
Bb Bb
Problem 8: A test cross uses an individual that is homozygous recessive. It will determine if the dog in question is pure or carrying a recessive gene.
B B bb
B b bb b
b
B b
Bb
Bb
bb
bb
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Multiple alleles
• Traits that are controlled by more than 2 alleles• Results in multiple phenotypes• Examples:
– Pigeons BA dominant over BBA and B are dominant over b
– Blood groups in humansFour blood types A B AB & O
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X-linked InheritanceExamples: Hemophilia, Color Blindness, Loss of Hearing & Muscular Dystrophy
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X-linked Recessive Inheritance
___% NORMAL HEARING of TOTAL OFFSPRINGS,
___ % HEARING LOSS of TOTAL OFFSPRINGS
___% NORMAL HEARING OF FEMALES
___ % HEARING LOSS OF MALES
XDXd
XD
XdYXDY
XDXD
Y
XD
Xd
XDXd XDY
XdYXDXdXDYXDXD
75
10050
25
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Polygenic Inheritance
A pattern of a trait that is controlled by 2 or more genes. Phenotype express a range of variability.
• Examples:– Stem length, human height, eye color & skin colorStem length for a totally recessive plant is____ cm.
aabbcc = 4 cm AABBcc = cm Aabbcc = cm AABBCc = cmAAbbcc = cm AABBCC = cmAABbcc = cm
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Gene Expression• Influence of External Environment:• Examples: Temp., nutrition, light, chemicals
– Color of rabbit in the summertime: brown– Color of rabbit in the winter: white– The temperature effects what color fur (or
what proteins) are expressed– Temp also determines the sex of a gator – Light determines color of bacteria
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Gene Expression
• Influence of Internal Environment:
• Examples: Hormonal influences – Horn size in mountain sheep– Male pattern baldness– Peacock feathers
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Gene Expression
• Influence of Internal Environment:
• Examples: Hormonal influences – Horn size in mountain sheep– Male pattern baldness– Peacock feathers
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Nature vs. Nurture
• In many cases it is not only the genes that we have that determine what we look like
• Scenario: If identical twins (same DNA) were separated at birth and lived in 2 different environments and then brought together 25 years later would they look the same? Why or why not?
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Nature vs. Nurture
• Answer:
The identical twins would have similar features (eye color, size of nose, etc.) but may look very different. What they did throughout their lives effects what they look like
– For example: sun exposure, diet, hygiene, injuries, etc.