Gregor Mendel

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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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Mendels 7 contrasting traits
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Genetics Terms

• Define genes
• factors that control organisms 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
b
B
B
b
b
b
B
b
B
b
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Three Laws by Mendel

• 1. 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
ProblemCross homozygous dominant with
homozygous recessive

• R red
• r white
• RR x rr

R R
Rr
Rr
r r
ResultsPhenotype Genotype
Rr
Rr
100 red
100 heterozygous
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2. Law of Segregation Mendels 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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Example of Segregation
ProblemCross two offspring from 1st cross (2
heterozygous parents)

• R red
• r white
• Rr x Rr

R r
RR
Rr
R r
Phenotype ____ red, ____ white ___ red
___ white Genotype
___ homozygous dominant, ___ homozygous
recessive, ___ heterozygous
75
25
Rr
rr
1
3
25
25
50
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3. Law of Independent Assortment Mendels 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 Cross
ProblemCross homozygous tall and homozygous
wrinkled seeds with homozygous short and
homozygous smooth seeds
What are the genotypes for these plants?
TTQQ x ttqq
T tallt short Q wrinkledq smooth
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TTQQ x ttqq
TQ
TQ
TQ
TQ
TtQq
TtQq
tq
TtQq
TtQq
TtQq
TtQq
TtQq
TtQq
tq
tq
TtQq
TtQq
TtQq
TtQq
tq
TtQq
TtQq
TtQq
TtQq
Phenotype 100 Tall Wrinkled
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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 dont 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
tq
TQ
tQ
Tq
TtQQ
TTQq
TtQq
TTQQ
TQ
TTQq
TtQq
Ttqq
TTqq
Tq
TtQQ
TtQq
ttQq
ttQQ
tQ
tq
TtQq
Ttqq
ttQq
ttqq
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What are the phenotypes for the above cross???

• - Tall Wrinkled
• - Tall smooth
• - Short wrinkled
• - Short smooth

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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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Example of Incomplete Dominance
R r
ProblemCross offspring from 1st cross (2
heterozygous parents)
Rr
RR

• R red
• r white
• Rr x Rr

R r
rr
Rr
ResultsPhenotype ___ red, ___ pink, ___
white Genotype

___ homozygous dominant
___ heterozygous ___
homozygous recessive
50
25
25
1
2
1
Ratio ___ ___ ___
25
50
1
2
1
Ratio ___ ___ ___
25
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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 Cattle
?
X
Roan Cattle
White Cattle
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Example of Codominance
R r
ProblemCross offspring from 1st cross (2
heterozygous parents)
Rr
RR

• R red
• r white
• Rr x Rr

R r
rr
Rr
ResultsPhenotype ___ red, ___ red white,
___ white Genotype

___ homozygous dominant
___ heterozygous __
_ homozygous recessive
50
25
25
1
2
1
Ratio ___ ___ ___
25
50
1
2
1
Ratio ___ ___ ___
25
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Problem 1
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
Homozygous dominant
Tall
TT
Short
tt
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Problem 2A married couple want to know their
chances of having girl
X Y
XX
XY
X X
__ __ x __ __
X
Y
X
X
XY
XX
Results Phenotype 50 male, 50 female
Phenotype ratio 2 male 2 female
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R r
Problem 3 Cross two heterozygous parents
RR
Rr

• R red
• r white
• __ __ x __ __

R r
Rr
rr
R
r
r
R
Phenotype ___ red, white ___ Phenotypic
Ratio __ ___
Genotype ___ heterozygous ___
homozygous dominant ____
homozygous recessive
75
25
1 white
25
3 red
50
25
25
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R R
Problem 4 Pure dominant crossed with hybrid
RR
RR

• R red
• r white
• __ __ x __ __

R r
Rr
Rr
R
R
R
r
Results Phenotype ___ red, white
___ Phenotype Ratio __ _ _ __
Genotype ___ heterozygous
___ homozygous dominant ___
homozygous recessive
100
0
4 red
4 white
50
50
0
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Problem 5 The males genotype is homozygous
recessive. The female is phenotypically dominant
but does carry the recessive allele.
r r
Rr
Rr

• R red
• r white
• __ __ x __ __

R r
rr
rr
r
r
r
R
50
50
Phenotype ___ red, white ___ Phenotypic
Ratio __ ___ Genotype
___ heterozygous ___ homozygous
dominant ___ homozygous
recessive
2 red
2 white
50
0
50
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Problem 6 Law of Codominance
R r
Cross two heterozygous parents
Rr
RR

• R red
• r white
• __ __ x __ __

R r
Rr
rr
R
r
r
R
Results Phenotype ___ red, ___ red and
white, white ___ Phenotypic Ratio __ red
__ red and white ___ white Genotype ___
heterozygous ___ homozygous
dominant ___ homozygous
recessive
25
25
50
1
2
1
50
25
25
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Problem 7 Law of Incomplete Dom
R r
RR
Rr
Cross two heterozygous parents

• R red
• r white
• __ __ x __ __

R r
Rr
rr
R
r
r
R
Results Phenotype ___ red, ___ pink,
white ___ Phenotype Ratio __ red __
pink ___ white Genotype ___ heterozygous
___ homozygous dominant
___ homozygous recessive
25
50
25
1
2
1
50
25
25
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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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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
Bb
b b
Bb
Bb

• B brown
• b white
• __ __ x __ __
• or
• __ __ x __ __

B
B
b
b
B b
Bb
bb
b b
B
b
b
b
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 B
• BA and B are dominant over b
• Blood groups in humans
• Four 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
XDXd
XDY
XD
Xd

• ___ NORMAL HEARING of TOTAL OFFSPRINGS,
• ___ HEARING LOSS of TOTAL OFFSPRINGS
• ___ NORMAL HEARING OF FEMALES
• ___ HEARING LOSS OF MALES

XDXd
XDXD
XD
XdY
XDXd
XDY
XDXD
XdY
XDY
Y
75
25
100
50
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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 color
• Stem length for a totally recessive plant is____
  cm.
• aabbcc 4 cm AABBcc cm
• Aabbcc cm AABBCc cm
• AAbbcc cm AABBCC cm
• AABbcc 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.