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Story of GeneticsGregor Mendel
Genetic
Problem
Solving
I
Genetic Problem SolvingEach gamete has one gene for each
trait.
After fertilization the new organism has two genes for each trait (Genotype).
Genetic Problem SolvingIf 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.
Dominant vs. RecessiveOnly 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.
Punnet SquaresPunnet 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.
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)
Punnet Square Practice
R
R
r
r
Male
Female
RR
r r
Rr
rR
Definitions
Genotype– is the genetic make up of an individual represented by the two alleles
eg RR .
– Phenotype is how the genetic trait appears in the individual – eg tongue roller
GenotypeOffspring have a
25% change of being RR
50% chance of being Rr
25% chance of being rr
Offspring have a 75% chance of being able to roll their tongues
And a 25% chance they can not roll their tongue
Phenotype
Try This2. In pea plants, yellow peas are
dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a heterozygous plant and a purebred plant with green peas.
Genetic Problem Solving
Each gamete has gene for each trait. After fertilization the new organism has genes for each trait (Genotype).
If the two in the genotype are the same, then the organism is said to have a
genotype and is .If the alleles are different then the organism is
.Punnet Squares are used to determine the
of an offspring having a particular .
We can also work out what the expected will be.
A punnet square is made by comparing all the possible combinations of from the
with those from the .
onetwo
alleles
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.
Punnet Square Practice
Complete worksheet “More Punnet Practice”