Genetics

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Genetics

• The Scientific Study of Inheritance

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Terms

• Allele
• Barr body
• Codominance
• Dihybrid cross
• Dominant
• Epistasis
• Genotype
• Heterozygous
• Homozygous

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• Inbreeding
• Incomplete dominance
• Linkage
• Locus
• Multi-allelic
• Phenotype
• Pleiotropy
• Polygenic
• Recessive
• Sex-linked

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Gregor Mendel

• Monk
• Austria Czech republic
• 1st to analyze inheritance in a
  scientific manner
• Scientific method
• Careful record-keeping

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Gregor Mendel

• Studied garden peas
• Easy to grow
• Produce lots of offspring
• Easily distinguished
  characteristics
• Fruit flies - today

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Gregor Mendel

• Parents pass factors to their offspring that
  are responsible for traits
• Factors genes
• Garden peas self-pollinate
• True-breeding parents
  produce offspring identical to
  themselves

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Gregor Mendel

• Control cross-pollination
• Cross-pollination produced
  hybrids
• Called a cross
• Hybrids offspring with
  mixed traits
• Traits inherited characteristic

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Crossed pure-breeding and got one trait. What
happened to the white trait?
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Gregor Mendel

• Allowed F1s to self-pollinate
• Produced F2 generation
• F2s 705 purple 224 white
• 31 ratio
• The heritable factor for white was masked but
  was not destroyed

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Gregor Mendel - 4 Hypotheses

• There are alternate forms for factors that
  control heredity
• For each characteristic, there are 2 factors
  inherited one from each parent
• 3. A gamete carries only one form for each
  factor during fertilization, the 2 factors
  unite
• 4. One form of the factor is fully expressed
  (visible) and the other has no effect

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Law Of Dominance
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Modern Genetics

• Factors genes
• Alternate forms alleles
• Genes sections of DNA code for making proteins
• Expression of proteins determines trait
• Dominant Allele allele that IS expressed
  protein is expressed (made)
• Recessive Allele allele that is NOT expressed
  (made) or masked protein is not made

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Structure Of A Chromosome

• Chromosomes are homologous pairs
• Same size, banding, centromere location and genes
• Made of DNA
• Sections of chromosomes are genes

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Chromosome 1
Homologue

Gene
Allele
Allele

Two alleles to a gene alleles may be dominant or
recessive
From mom
From dad
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Modern Genetics

• Genotype an organisms genetic makeup
• PP
• Phenotype an organisms expressed or physical
  traits
• Purple

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Mendels Principle of SegregationLaw of
Segregation
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Principle of Segregation

• All organisms have 2 sets of homologous
  chromosomes one from each parent
• Diploid
• One allele located on each chromosome one from
  mom, one from dad
• 2 alleles 1 gene

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Principle of Segregation

• Pairs of alleles separate (segregate) during
  gamete formation
• 1 form of a factor goes into 1 gamete while the
  other form separates and goes into another gamete
  (handout)
• Locus location of a gene on a chromosome loci
  (pl.)
• Alleles are at the same locus on each homologous
  chromosome

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Principle of Segregation

• Homozygous both alleles for the trait are the
  same (homo)
• PP, pp homozygous
• Heterozygous the two alleles are different
• Pp heterozygous

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Fertilization

• During fertilization, the sperm unites with the
  egg
• 1 haploid sperm 1 haploid egg 1 diploid
  zygote
• Which sperm unites with which egg is by random
  chance
• Flipping a coin

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This is too hard to do!!!!
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Use The Laws of Probability

• Probability chance that something will occur
• How can we predict what will happen easier?
• Punnett Square
• How does it work, you say?
• Im so glad you asked

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Punnett Square

• Use letters to represent each allele
• a. Use the CAPITAL for dominant and small case
  for recessive
• b. Ex. P purple p white
• T tall t short
• Y yellow y - green

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2. Draw a square
PURPLE x white
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• Determine what letters to use to represent the
  alleles
• Example
• a. Cross a PURPLE with a white flower
• b. PURPLE is dominant over white in pea plants
  so use P PURPLE and p white
• c. Every gene has 2 alleles so use 2 letters

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pp
PP
Crossing a homozygous purple flower with a
homozygous recessive white flower
pp
X
PP
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• Separate letters (alleles) around the square
  this represents segregation

PP
BE CAREFUL HOW YOU MAKE YOUR LETTERS!!
P
P
p
pp
p
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5. Combine the letters (alleles) into each box
of the square
PURPLE PP x white pp
P
P
p
P
P
p
p
p
P
P
p
p
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6. Determine the results
PP x pp 4 Pp and 4 PURPLE
P
P
2
Pp
Pp
1
Genotype 4 Pp Phenotype 4 PURPLE
p
Purple
Purple
3
4
Pp
Pp
p
Purple
Purple
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Results

• Genotype combination of letters (alleles)
• Pp
• Phenotype appearance (what do they LOOK like?
• Purple

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What If You Crossed heterozygous purple with
heterozygous purple?
Pp
Pp
Pp x Pp
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Separate letters (alleles) around the square
Pp
P
p
P
Pp
p
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Combine the letters (alleles) in the squares
P
p
P
P
P
p
P
Purple
Purple
P
p
p
p
p
Purple
white
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Genotypes
Pp x Pp
1 - PP
p
P
2 - Pp
1- pp
P
PP
P
p
Phenotypes
Purple
Purple
pp
Pp
3 - PURPLE
p
1 - white
Purple
white
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6. Determine the results
PP x pp 4 Pp and 4 PURPLE
P
P
2
Pp
Pp
1
Genotype 4 Pp Phenotype 4 PURPLE
p
Purple
Purple
3
4
Pp
Pp
p
Purple
Purple
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Practice Problems

• Tall is dominant to short
• What genotypic and phenotypic results would be
  expected if you crossed a HOMOZYGOUS tall with a
  HOMOZYGOUS short?

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Practice Problems

• What genotypic and phenotypic results would
• be expected if you crossed a HOMOZYGOUS tall
• with a HOMOZYGOUS short?

T
T
t
t
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T
T
Genotypes -
4 - Tt
Tt
Tt
t
Phenotypes -
Tall
Tall
4 - tall
Tt
Tt
t
Tall
Tall
100 tall
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Practice

• In pea plants, yellow is dominant to green. What
  results would be expected if you crossed a
  homozygous yellow with a homozygous green?
• Homozygous same
• Yellow Y green y
• Homozygous yellow YY
• Homozygous green yy

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Y
Y
Genotype 4 Yy
Yy
Yy
Phenotype 4 yellow 100 yellow
y
Yellow
Yellow
Yy
Yy
y
Yellow
Yellow
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Practice

• Black fur is dominant to brown fur in mice. What
  results should you expect if you crossed a
  homozygous black with a homozygous brown?
• Black is dominant so use B brown - b
• Homozygous black BB
• Homozygous brown bb

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B
B
Genotype 100 Bb
Bb
Bb
b
Black
Black
Phenotype 100 black
Bb
Bb
b
Black
Black
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Law of Independent Assortment
Are Traits Inherited Together (dependently) or
Separately (independently)?
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Law of Independent Assortment

• Round (R) is dominant to wrinkled (r)
• Yellow (Y) is dominant to green (y)
• Result from crossing two traits?
• If you inherit a dominant trait does the other
  trait also have to be dominant?
• Dihybrid cross result of crossing two traits
  together

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Dihybrid Cross

• Homozygous (pure-breeding) round (RR), and yellow
  (YY) with
• Homozygous recessive wrinkled (rr), green (yy)

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Dihybrid Cross

• Are the two traits inherited together (in a
  package) or can they be inherited separately?
• Mendel crossed the Ps (yellow, round x green,
  wrinkled)
• F1s were all dominant (yellow, round)
• Allowed the F1s to self-pollinate

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Dihybrid Cross

• 9331 ratio
• 9/16 yellow, round
• 3/16 yellow, wrinkled
• 3/16 green, round
• 1/16 green, wrinkled

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Independent Assortment
Parent 1 2
YyRr
yr
yR
Yr
YR
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Law of Independent Assortment
Yy Rr
Yy Rr
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Law of Independent Assortment

• Each pair of alleles segregates independently of
  other pairs of alleles
• Can recombine independently of each other
• Genetic variation
• Biggest cause of genetic variation in sexually
  reproducing organisms

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Independent Assortment

• Budgies inherit two colors INDEPENDENTLY
• Color (Yellow) or no color on the
  outer surface of the feather
• Melanin or no melanin in the
  inner core of the feather

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Variation and Patterns of Variation

• Wild type - most common traits in the wild
• Budgies green feathers
• Knowing patterns and rules of
  inheritance allows breeders to
  produce blues, yellows, and
  whites

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Budgie Color

• Two genes inherited separately
• Outside color of feather
• Inside color of feather
• Independent assortment the two characteristics
  are inherited independently of each other

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Green Y_B_
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Blue yyB_
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Yellow Y_bb
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White yybb
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Test Cross

• How can We Use Genetics to Determine if Our
  Organism is Pure-breeding?

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Test cross

• Mate an individual whose genotype is not known
  (dominant phenotype) with a homozygous recessive
  for that trait
• Ex. Is your favorite Labrador a pure black or
  does he carry a recessive allele?

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Test cross

• Cross the unknown with a homozygous recessive
• Eight puppies born, 3 are brown (recessive)
• ?

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B
B
b
Bb
Bb
b
Bb
Bb
If the unknown is homozygous (pure) then all the
offspring are dominant
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B
b
b
Bb
bb
b
Bb
bb
If the unknown is heterozygous (carrier) then
some offspring are recessive
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Variations of Mendel

• Complete dominance
• Incomplete dominance
• Codominance
• Multiple alleles
• Pleiotropy
• Polygenic inheritance
• Linkage

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Incomplete Dominance

• Dominant allele does not totally mask recessive
  allele
• Some recessive trait is expressed blended
  
• Red x white pink

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Curly hair straight hair wavy
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Incomplete Dominance

• Heterozygotes express a trait between the
  dominant and recessive
• Familial
  hypercholesterolemia
• hh very high
  cholesterol
• Hh mild cholesterol
• HH low cholesterol normal

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Codominance

• Both traits are EQUALLY dominant
• Both traits are expressed (not blended)
• Roan color
• Sickle cell
• Blood types

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Codominance

• Two different traits and both show equally
• Roan color
• Blood types

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Blood Types

• Antigens proteins on the surface of red blood
  cells (RBCs)
• Antibodies proteins floating in the plasma of
  blood that bind with foreign proteins
  (antigens)
• Antibodies stick to foreign antigens forming a
  clot

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Blood Types

• B into A causes a clot
• A into B causes a clot

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Blood Types

• Antibodies will be the opposite of the antigens
• A blood will have B antibodies
• B blood will have A antibodies
• Antibodies are like guard dogs they attack
  foreign cells with the wrong antigens

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Blood Types

• Codominance
• Multiple alleles 1 gene but three possible
  allele combinations
• A, B, O

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Blood Types Phenotypes

• Antigens proteins on the surface of cells
  (RBCs)
• Cell-to-cell recognition
• Antibodies proteins floating in the plasma of
  blood that bind with foreign proteins (antigens)

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Blood Types Phenotypes

• Antibodies agglutinate to antigens that are
  foreign
• Agglutinate clot, clump
• B into A causes agglutination

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Blood Types Phenotypes

• Blood type type of antigens on the surface
• Antibodies will be the opposite of the antigens
• A blood will have B antibodies

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A antigens
A
B Antibodies
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B antigens
B
A Antibodies
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Person with A blood
B antigens
B
B antibodies attach to B antigens causes blood
to agglutinate
B Antibodies
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Person with B blood
A antigens
A
A antigens are attacked by A antibodies
A Antibodies
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A, B antigens
Person with AB blood
AB
No antibodies
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No antigens
Person with O blood
O
A and B antibodies
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Blood Types Genotypes

• Dominant allele I
• Recessive allele i (inability)
• II, Ii, ii
• Dominant allele can carry A or B
• Ia or IB

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Blood Types

• 2 alleles for each gene
• A IAIA or IA i
• B IBIB or IB i
• AB IAIB
• O (zero) ii

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How to do Punnett Squares With Blood Types
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Heterozygous
IA
i
Homozygous
IAIA
IA i
IA
IAIA
IA i
IA
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Can 2 people With A and B Blood Have a Child With
O Blood?
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Heterozygous A
IA
i
Heterozygous B
IAIB
IB i
IB
B
AB
i i
IA i
i
O
A
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Pleiotropy

• One gene has multiple effects
• Sickle-cell anemia p. 160
• Abnormal blood cells
• Difficulty breathing
• Brain, heart, kidney damage

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Pleiotropy Heterozygote Advantage

• High incidence of sickle-cell in areas where
  there is a lot of malaria
• Malaria does not effect sickle-cell
• People w/ sickle-cell dont suffer malaria

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Polygenic Inheritance

• Multiple genes produces a continuous effect very
  dark-very light
• Skin, hair, eye color
• 6 10 alleles
• AABBCC - aabbcc

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Linkage

• Early 1900s TH Morgan
• Fruit flies
• Inheritance patterns did not follow Mendelian
  Laws of Probability (?)
• Genes are linked

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Linkage

• Genes on the same chromosome are inherited
  together
• Sex linked genes
• Gene located on the sex chromosome (usually X)

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Sex linkage and Punnett Squares
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Linkage

• The sex-linked trait is usually on the X
  chromosome
• X X female
• X Y male
• XH normal
• Xh hemophilia

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Hemophilia

• Sex-linked, recessive disorder
• Bleeders disease lack protein
  for blood clotting
• Czar Nicholas son Nicki

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Normal phenotypes
XH
XH
XH
XH XH
XH XH
Y
XH Y
XH Y
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Hemophilia phenotype
XH
Xh
XH
XH XH
XH Xh
Y
XH Y
Xh Y
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Sex-linked Traits

• Hemophilia
• Duchennes Muscular dystrophy
• Color-blindness
• Mostly males
• Smartness

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Sex-linked Traits Y Chromosome

• Maleness

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Human Disorders

• Single gene
• 2 types
• Dominant expression
• Recessive expression

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Human Disorders Dominant

• Only requires one allele for trait to
  be expressed
• Polydactyly multiple fingers
• Achondroplasia dwarfism,
  heterozygotes

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Human Disorders Dominant

• Most dominant disorders are not lethal
• Huntingtons disease midlife expression,
  degeneration of the nervous system
• Hypercholesterolemia high cholesterol heart
  disease

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Human Disorders Recessive

• Homozygous for the disorder to be expressed
• Cystic fibrosis
• Sickle cell anemia
• Tay-Sachs disease
• PKU

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Fetal Testing

• Chorionic villus sampling (CVS) fetal cells
  removed from placenta
• Karyotyped quickly

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Recessive Disorders

• Cystic fibrosis whites build up of mucus in
  lungs, pancreas

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Recessive Disorders

• Sickle cell anemia Black and SE Asia 1/500
  (lethal), 1/10 carrier
• Codominant one allele is normal, other forms
  hemoglobin that crystallizes in low oxygen

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Recessive Disorders

• Tay-Sachs Jewish lack gene that produces
  enzyme that breaks down lipids in the brain
  causes brain degeneration, lethal by age 3-4
• PKU phenylketonuria lack the gene needed to
  make the enzyme that breaks down phenylalanine.
  Phenylalanine accumulates causing nervous
  disorders. Treated with diet

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Fetal Testing

• Amniocentesis removal of amniotic fluid
  (surrounds the developing baby) 20 ml
• Biochemical tests (spina bifida, infections)
• Cells karyotyping (Downs, Tay-Sachs)

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Fetal Testing

• Ultrasound view of baby
• Fetoscopy direct view of
  baby

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Pedigrees

• Tracing traits back over generations
• Dominance does NOT mean that a phenotype is
  normal or more common
• Wild type

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Pedigrees

• Used to predict probability of genetic disorders
• Carriers individuals who do not express the
  trait but have the recessive allele in their
  genotype

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Pedigrees

• Dominance heterozygote displays the trait
• Recessive expression occurs only if the genotype
  is homozygous
• bb, tt, ff

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Pedigree

• Family tree
• Shows how a trait is passed down from one
  generation to the next
• male
• female

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Pedigree number 1
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Pedigree number 2
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Pedigree number 3
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