Story of Genetics Gregor Mendel

Genetic Problem Solving Each gamete has one gene for each trait. After fertilization the new organism has two genes for each trait (Genotype).

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.

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.

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.

Punnet Square Practice 1. 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 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

Genotype Offspring 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 This 2. 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. one two alleles

Try This 3. 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”