Observable Patterns of Inheritance

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Observable Patterns of Inheritance
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Can you do this?
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Terms to Know

• Probability
• True-breeding
• Hybrid
• Segregation
• Traits
• Genes

• Homozygous
• Heterozygous
• Phenotype
• Genotype
• Dominant
• Recessive

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Genes

• Chemical factors that determine traits (units of
  information)
• Analogy Genes are like a combination of
  ingredients in a recipe. They code for a specific
  food.
• Passed from parents to offspring
• Each has a specific location (locus) on a
  chromosome

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Alleles

• Different forms of a gene (back to
  analogyreplacing jiffy p.b. with skippy p.b.)
• Dominant allele (Uppercase letter) overrules a
  recessive allele (lowercase letter) that it is
  paired with

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Allele Combinations

• Homozygous purebred
• having two identical alleles at a locus
• AA (dominant expressed) or aa (recessive
  expressed)
• Heterozygous hybrid
• having two different alleles at a locus
• Aa (dominant expressed)

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Genotype Phenotype

• Genotype refers to particular genes an individual
  carries
• Phenotype refers to an individuals observable
  traits
• Cannot always determine genotype by observing
  phenotype

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Tracking Generations

• Parental generation P
• mates to produce
• First-generation offspring F1
• mate to produce
• Second-generation offspring F2

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Earlobe Variation

• Whether a person is born with attached or
  detached earlobes depends on a single gene
• Gene has two molecular forms (alleles)

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Earlobe Variation

• You inherited one allele for this gene from each
  parent
• Dominant allele specifies detached earlobes (E)
• Recessive allele specifies attached earlobes (e)

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Dominant Recessive Alleles

• If you have attached earlobes, you inherited two
  copies of the recessive allele
• If you have detached earlobes, you may have
  either one or two copies of the dominant allele

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Early Ideas About Heredity

• People knew that sperm and eggs transmitted
  information about traits
• Blending theory
• Problem
• Would expect variation to disappear
• Variation in traits persists

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Gregor Mendel

• Strong background in plant breeding and
  mathematics
• Using pea plants, found indirect but observable
  evidence of how parents transmit genes to
  offspring

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• Mendel was born in1822
• Austrian monk
• Studied at the Univ. of Vienna
• Teacher (High School)

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Figure 245 The Structure of a Flower
Section 24-1
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The Garden Pea Plant

• Self-pollinating
• True breeding (different alleles not normally
  introduced)
• Can be experimentally cross-pollinated

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How did Mendel fertilize the plants?
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F1 Results of One Monohybrid Cross
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F
M
Dominant trait is expressed
Recessive appears
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Figure 11-3 Mendels Seven F1 Crosses on Pea
Plants
Seed Shape
Flower Position
Seed Coat Color
Seed Color
Pod Color
Plant Height
Pod Shape
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
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F1 Results of Mendels Dihybrid Crosses

• All plants displayed the dominant form of both
  traits
• We now know
• All plants inherited one allele for each trait
  from each parent
• All plants were heterozygous (AaBb)

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Principle of Dominance

• Some alleles are dominant and others are
  recessive.

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• Mendel wanted to know if the recessive alleles
  disappeared or are they still in the f1,just
  hidden.

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Principles of Dominance
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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Principles of Dominance
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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Principles of Dominance
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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Mendels Theory of Segregation

• An individual inherits a unit of information
  (allele) about a trait from each parent
• During gamete formation, the alleles segregate
  from each other

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Independent Assortment

• Mendel concluded that the two units for the
  first trait were to be assorted into gametes
  independently of the two units for the other
  trait
• Members of each pair of homologous chromosomes
  are sorted into gametes at random during meiosis

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Independent Assortment
Metaphase I
OR
A
A
A
A
a
a
a
a
B
B
B
B
b
b
b
b
Metaphase II
A
A
A
A
a
a
a
a
B
B
B
B
b
b
b
b
Gametes
B
B
B
B
b
b
b
b
A
A
A
A
a
a
a
a
1/4 AB
1/4 ab
1/4 Ab
1/4 aB
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F2 Results of Monohybrid Cross
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The physical characteristic
Type of alleles
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Impact of Mendels Work

• Mendel presented his results in 1865
• Paper received little notice
• Mendel discontinued his experiments in 1871
• Paper rediscovered in 1900 and finally
  appreciated

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Probability

• The likelihood that a particular event will
  occur.
• Flip a coin.
• We use Punnett Squares

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• D 38- Deduce the probable mode of inheritance of
  traits (e.g.,

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Punnett Squares of Test Crosses

Two phenotypes
All dominant phenotype
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Punnett Square of a Monohybrid Cross
Dominant phenotype can arise 3 ways, recessive
only one
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Test Cross

• Individual that shows dominant phenotype is
  crossed with individual with recessive phenotype
• Examining offspring allows you to determine the
  genotype of the dominant individual

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Tt X Tt Cross
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Tt X Tt Cross
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Tt X Tt Cross
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Genetics Practice Problem 1

• What occurs when a purple plant that is
  heterozygous is fertilized by a white plant?
• Identify generations
• Punnett Square
• Genotypes
• Phenotype

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Principle of Independent Assortment

• The genes for different traits separate
  independently of one another during the formation
  of gametes.

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Figure 11-10 Independent Assortment in Peas
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• Yellow round 9/16
• Green round 3/16
• Yellow wrinkled 3/16
• Green wrinkled 1/16
• 9 3 3 1 Ratio

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Dihybrid Cross

• Experimental cross between individuals that are
  homozygous for different versions of two traits

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Straight Pinky (Dominant) Bent Pinky (Recessive)
Straight Thumb (Dominant) Curved Thumb
(Recessive)
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More Dominant Traits
Polydactylism
Achondroplastic Dwarfism
Tay-Sachs Disease - One Wrong Letter
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Dominance Relations

• Complete dominance
• Incomplete dominance
• Heterozygote phenotype is somewhere between that
  of two homozyotes
• Codominance
• Non-identical alleles specify two phenotypes that
  are both expressed in heterozygotes

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Flower Color in Snapdragons Incomplete
Dominance

• Red-flowered plant X White-flowered plant
• Pink-flowered F1 plants

(homozygote)
(homozygote)
(heterozygotes)
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Flower Color in Snapdragons Incomplete Dominance

• Red flowers - two alleles allow them to make a
  red pigment
• White flowers - two mutant alleles cant make
  red pigment
• Pink flowers have one normal and one mutant
  allele make a smaller amount of red pigment

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Figure 11-11 Incomplete Dominance in Four OClock
Flowers
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Figure 11-11 Incomplete Dominance in Four OClock
Flowers
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Flower Color in Snapdragons Incomplete Dominance

• Pink-flowered plant X Pink-flowered plant
• White-, pink-, and red-flowered plants
• in a 121 ratio

(heterozygote)
(heterozygote)
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Incomplete Dominance
Neither allele is dominant over the other
Combination of red and white flowers
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Codominant

• Sickle Cell Disease
• ABO Blood Types

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Pleitropy

• Alleles at a single locus may have effects on two
  or more traits
• Classic example is the effects of the mutant
  allele at the beta-globin locus that gives rise
  to sickle-cell anemia

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Teachers Domain - A Mutation Story
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Genetics of Sickle-Cell Anemia

• Two alleles
• 1) HbA
• Encodes normal beta hemoglobin chain
• 2) HbS
• Mutant allele encodes defective chain
• HbS homozygotes produce only the defective
  hemoglobin suffer from sickle-cell anemia

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Pleiotrophic Effects of HbS/HbS

• At low oxygen levels, cells with only HbS
  hemoglobin sickle and stick together
• This impedes oxygen delivery and blood flow
• Over time, it causes damage throughout the body

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Blood Typing

• Karl Landsteiner 1897
• Worked at the Univ. of Vienna, Vienna Austria
  (Sound familiar?)
• Wanted to find out which red blood cells would
  clot

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• First found two different groups, A and B
• Third group would not clot when exposed to A or B
  What do you think this was?
• What about the forth group?

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Genetics of ABO Blood Types Three Alleles

• Gene that controls ABO type codes for enzyme that
  dictates structure of a glycolipid on blood cells
• Two alleles (IA and IB) are codominant when
  paired
• Third allele (i) is recessive to others

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ABO Blood Type Glycolipids on Red Cells

• Type A - Glycolipid A on cell surface
• Type B - Glycolipid B on cell surface
• Type AB - Both glyocolipids A B
• Type O - Neither glyocolipid A nor B

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ABO Blood TypeAllele Combinations

• Type A - IAIA or IAi
• Type B - IBIB or IBi
• Type AB - IAIB
• Type O - ii

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ABO and Transfusions

• Recipients immune system will attack blood cells
  that have an unfamiliar glycolipid on surface
• Type O is universal donor because it has neither
  type A nor type B glycolipid

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Codominance and Multiple Alleles - AB or NOT AB
Codominance - both alleles are dominant IA and
IB Multiple Alleles - genes have more than two
alleles IA, IB, Ia
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Figure 14-4 Blood Groups
Safe Transfusions
Antigen on Red Blood Cell
Phenotype (Blood Type
Genotype
From
To
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Universal Acceptor
Universal Donor
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Rh factor - Another Blood Trait

• Pregnancy complications
• Rh is a type of protein in the blood
• If an Rh- man reproduces with an Rh woman
  complications can occur.

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Polygenic Traits Desirees Baby Case Study

• More than one gene controls a trait
• Skin color more than one gene, incomplete
  dominance

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A,B and C are dark
a,b and c are light
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Sex Linked Traits - traits that are carried on
the either the x or y chromosome
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Figure 14-13 Colorblindness
Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
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Figure 14-13 Colorblindness
Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
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Colorblindness
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Sex-Linked Disorder
Cystic Fibrosis - Finding Cures is Hard
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Male Pattern Baldness (X chromosome)
Hairy Pinna - long hair on ears
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Recessive Disorder
Figure 14-8 The Cause of Cystic Fibrosis
Chromosome 7
CFTR gene
The most common allele that causes cystic
fibrosis is missing 3 DNA bases. As a result,
the amino acid phenylalanine is missing from the
CFTR protein.
Normal CFTR is a chloride ion channel in cell
membranes. Abnormal CFTR cannot be transported
to the cell membrane.
The cells in the persons airways are unable to
transport chloride ions. As a result, the airways
become clogged with a thick mucus.
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Albinism

• Phenotype results when pathway for melanin
  production is completely blocked
• Genotype - Homozygous recessive at the gene locus
  that codes for tyrosinase, an enzyme in the
  melanin-synthesizing pathway

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Human Genetics
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Tracing Genes Through Families - Human Pedigrees
Female
Partner
Male
Brothers and Sisters
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Figure 14-3 A Pedigree
A circle represents a female.
A square represents a male.
A horizontal line connecting a male and female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A half-shaded circle or square indicates that a
person is a carrier of the trait.
A circle or square that is not shaded indicates
that a person neither expresses the trait nor is
a carrier of the trait.
A completely shaded circle or square indicates
that a person expresses the trait.
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Ability to roll the tongue in the Senator Family
Tongue Roller - dominant, Non-Tongue Roller -
recessive White tongue roller, Purple
non-roller
What are the genotypes of everyone? R roller, r
non roller
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George, Sam, Ann, Michael, Daniel and Alan are
Rr Arlene, Tom, Wilma, and Carla are rr Sandra,
Tina and Christopher are either RR or Rr
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Case Study - Hemophilia and the Royal Family
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1. First, lets take a look at Queen Victorias
son Leopolds family. His daughter, Alice of
Athlone, had one hemophilic son (Rupert) and two
other childrena boy and a girlwhose status is
unknown. a) What is the probability that her
other son was hemophilic? b) What is the
probability that her daughter was a carrier?
Hemophilic? c) What is the probability that both
children were normal?
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2. Now for the Spanish connection Victorias
youngest child, Beatrice, gave birth to one
daughter, one normal son, and two hemophilic
sons. Looking at the pedigree of the royal
family, identify which of Beatrices children
received the hemophilic gene why can you make
this conclusion? Notice that Beatrices daughter,
Eugenie, married King Alfonso XIII of Spain and
had six children, one of whom was the father of
Juan Carlos, the current King of Spain. Would you
predict that Juan Carlos was normal, a carrier,
or a hemophilic?
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3. Alexis did not die from hemophilia. At the age
of fourteen he was executed with the rest of the
family. His four oldest sisters were also young
and didnt have children, so we dont know
whether any of them was a carrier. But we can
make an estimate. a) What are the probabilities
that all four of the girls were carriers of the
allele hemophilia? b) Supposing Alexis had lived
and married a normal woman, what are the chances
that his daughter would be a hemophiliac? c) What
are the chances his daughters would be carriers?
d) What are the chances that his sons would be
hemophiliacs?
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Nondisjunction
Homologous chromosomes fail to separate
Meiosis I Nondisjunction
Meiosis II
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Nondisjunction
Homologous chromosomes fail to separate
Meiosis I Nondisjunction
Meiosis II
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Nondisjunction
Homologous chromosomes fail to separate
Meiosis I Nondisjunction
Meiosis II
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Epistasis

• Interaction between the products of gene pairs
• Common among genes for hair color in mammals

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Genetics of Coat Color in Labrador Retrievers

• Two genes involved
• - One gene influences melanin production
• Two alleles - B (black) is dominant over b
  (brown)
• - Other gene influences melanin deposition
• Two alleles - E promotes pigment deposition and
  is dominant over e

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Allele Combinations and Coat Color

• Black coat - Must have at least one dominant
  allele at both loci
• BBEE, BbEe, BBEe, or BbEE
• Brown coat - bbEE, bbEe
• Yellow coat - Bbee, BbEE, bbee

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Comb Shape in Poultry

• Alleles at two loci (R and P) interact
• Walnut comb - RRPP, RRPp, RrPP, RrPp
• Rose comb - RRpp, Rrpp
• Pea comb - rrPP, rrPp
• Single comb - rrpp

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Campodactyly Unexpected Phenotypes

• Effect of allele varies
• Bent fingers on both hands
• Bent fingers on one hand
• No effect
• Many factors affect gene expression

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Continuous Variation

• A more or less continuous range of small
  differences in a given trait among individuals
• The greater the number of genes and environmental
  factors that affect a trait, the more continuous
  the variation in versions of that trait

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Human Variation

• Some human traits occur as a few discrete types
• Attached or detached earlobes
• Many genetic disorders
• Other traits show continuous variation
• Height
• Weight
• Eye color

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Temperature Effects on Phenotype

• Himalayan rabbits are Homozygous for an allele
  that specifies a heat-sensitive version of an
  enzyme in melanin-producing pathway
• Melanin is produced in cooler areas of body

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Environmental Effects on Plant Phenotype

• Hydrangea macrophylla
• Action of gene responsible for floral color is
  influenced by soil acidity
• Flower color ranges from pink to blue