PUNETT SQUAREDiagram that determines the gene combinations that might result from a genetic cross

The letters in the Punnett Square represent alleles; capital letters represent Dominant Alleles and lower case letters represente Recessive Alleles.

T t

T TT Tt

t Tt tt

Tt

Tt

Mendel’s Experiments predicted a ratio of 3:1; this is , 3 dominant to 1 recessive. This predicts the average outcome of a large number of events. However, probability cannot predict the precise outcome of an individual event. The larger the number of offspring, the closer the resulting numbers will get to expected values.

homozygous

heterozygous

Organisms that have two identical alleles for a particular trait (TT or tt).These organisms are TRUE-BREEDING for this particular trait.

Organisms that have two different alleles for the same trait (TT or tt).These organisms are HYBRID for this particular trait.

PhenotypeGenetic makeup.Genetic information, combination of alleles.

Physical characteristics of the organism.What we can see.

GenotypeSome organisms may have the same PHENOTYPE, but different GENOTYPE.

For example, plants with genotypes TT, Tt, will look the same (they will have the same Phenotype).