genetic problem solving
DESCRIPTION
Genetic Problem Solving. I. Genetic Problem Solving. Each gamete has one gene for each trait. After fertilization the new organism has two genes for each trait (Genotype). Sperm, Egg or Zygote?. What the ?. Gene. Eye Colour Gene. Homozygous. Heterozygous. Hair Colour Gene. - PowerPoint PPT PresentationTRANSCRIPT
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Genetic Problem Solving
I
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Genetic Problem Solving Each gamete has one gene for
each trait.
After fertilization the new organism has two genes for each trait (Genotype).
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Sperm, Egg or Zygote?
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What the ?Gene
Homozygous
Eye Colour Gene
HeterozygousHair Colour
Gene
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Dominant vs. Recessive Only one allele is expressed in the
phenotype.
The allele which will always be expressed is called the Dominant allele.
The allele which may be hidden is called the Recessive allele.
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Punnet Squares Punnet Squares are used to
determine the probability of an offspring having a particular genotype.
We can also work out what the expected phenotype will be.
It is made by comparing all the possible combinations of alleles from the mother with those from the father.
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Punnet Square Practice1. If two parents are both
heterozygous for the tongue rolling gene, predict what genotype and phenotype their offspring may have.
Roller allele is dominant (R)Non-roller allele is recessive (r)
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Punnet Square Practice
RR
r
rMal
eFemale
RR
r r
Rr
Rr
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Genotype Offspring have a
25% change of being RR
50% chance of being Rr
25% chance of being rr
Phenotype Offspring have a
75% chance of being able to roll their tongues
And a 25% chance they can not
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Genotype vs. Phenotype Genotype: The specific alleles an
organism possesses for a trait (eg. BB, Bb or bb).
Phenotype: The physical trait an organism shows due to their genotype (Brown eyes or Blue eyes).
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Genetic Problem Solving If the two alleles in the genotype
are the same, then the organism is said to have a homozygous genotype and is pure breeding.
If the alleles are different then the organism is heterozygous.
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Try This2. Ms. Honeypot crossed a heterozygous
pea plant and a purebred plant with green peas in an attempt to create yellow peas.
In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring).
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Punnet Square Practice
yY
y
yHet
eroz
ygus
Purebred
Yy
yy
Yy
yy
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Try This3. In pea plants, round peas are
dominant over wrinkled peas.
Use a Punnett square to predict the phenotypic and genotypic outcome of a cross between a plant homozygous for round peas and a plant homozygous for wrinkled peas.
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Punnet Square Practice
rR
r
RRou
ndWrinkled
Rr
Rr
Rr
Rr
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Punnet Square Practice
Complete worksheet “More Punnet Practice”
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Oink Oink! (Try This!)
Farmer Ted has a curly tailed male pig and wants to know whether it is pure breeding or not. He has asked you (the genetics expert) to find out for him?
Curly tails (T) are dominant over straight tails (t).
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Female
Mal
eOink (Answer)
Mate the pig in question witha female pig with a straight tail.
tT
t
TTt
Tt
Tt
Tt
Female
Mal
e
tT
t
tTt
tt
Tt
tt
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Conclusions If the male was pure
breeding then 100% of F1 offspring would have curly tails.
If there were ANY F1 offspring with straight tails then the male pig would not be pure breeding.
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Test Cross In genetics a test cross is used to
determine if an individual exhibiting a dominant trait is homozygous or heterozygous.
Test crosses determine the genotype of an individual.
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Test Cross Test crosses involve breeding the individual in
question with another individual that expresses a recessive version of the same trait.
If all offspring display the dominant phenotype, the individual in question is homozygous dominant.
If any of the offspring displays a recessive phenotype, then the individual is heterozygous.