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”