 Probability can be used to predict the results of genetic crosses.  Probability- the likelihood that something is going to happen. In genetics expressed as a ratio or percentage. Ex: the probability that it will snow in March is 50:50

 Punnett Squares- A tool used to determine the gene combinations that might result from a genetic cross  A capital letter is used to represent the dominant allele  A lower case letter is used to represent the recessive allele.

 The principles of probability can be used to predict the outcomes of genetic crosses  This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants.

 Homozygous- Organisms that have two identical alleles for a particular trait organisms are true-breeding for a particular trait. Two alleles for black fur  Heterozygous- Organisms that have two different alleles for the same trait organisms are hybrid for a particular trait. One allele for white fur and one allele for white fur

 Genotype- genetic make up of the organism Ex: genes for black fur and white fur Ex: Tall (T) allele and short (t) allele  Phenotype- the physical characteristics or what the organisms looks like. Ex: the mouse has black fur. Ex: all plants appear tall

 The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).

 Genotypic Ratios 25% or 1:3 (TT to Tt or tt) likelihood the offspring will be TT 50% or 2:2 likelihood the offspring will be Tt 25% or 1:3 likelihood the offspring will be tt  Phenotypic Ratios 75% or 3:1 (tall to short) likelihood the offspring will appear Tall 25% or 1:3 likelihood the offspring will appear short

 In the F 2 generation; the ratio of tall plants (TT or Tt) to short (tt) plants is 3:1.  The predicted ratio showed up in Mendel’s experiments indicating that segregation of gametes did occur.

 Probabilities predict the average outcome of a large number of events.  Probability cannot predict the exact outcome of an individual event  In genetics, the larger the number of offspring, the closer the resulting numbers will get to the expected values.