 Genetics – the scientific study of heredity  Why the garden pea?  Easy to grow  Produce large numbers  Mature quickly  Reproductive organs in same flower (self fertilization or cross fertilization)

 Step 1 – produced pure breed plants – Parental or P generation  Self fertilized for many generations  Used seeds from these to produce offspring with one form of a particular trait  Step 2 – cross two varieties in the P generation  F1 generation – first filial  Crossed purple anthers and white stigmas  Produced only purple

 Step 3 – allow F1 to self-fertilize  F2 generation – second filial  White reappeared (3:1 ratio – purple to white)  Mendel developed a model to explain his results (Rules about inheritance)  Parents transmit information about traits to their offspring (factors)  Each individual has two factors from each trait (one from each parent)  Homozygous – same information  Heterozygous – different information

 Step 3 continued  Alternative forms of a factor – alleles  The alleles an organism possesses – genotype  Physical appearance (determined by the alleles) – phenotype  An individual possesses two alleles for each trait  The presence of an allele does not mean it will be expressed  Dominant – allele is expressed  Recessive – allele is NOT expressed (in heterozygous)

 Punnett square – diagram used to predict the results of a cross  Probability – the likelihood that something will happen

 Law of segregation – the members of each pair of alleles separate when gametes are formed  A gamete will receive one alleles or the other  Law of independent assortment – two or more pairs of alleles segregate independently of one another during gamete formation

 Genes combine according to the rules of probability  The probability of a gamete having an allele is 50% or one-half  Simple Punnett square is monohybrid  4 offspring

 Incomplete codominance (snapdragons)  Homozygotes – show red or white  Heterozygotes – show pink  Codominance  Both genes are fully expressed  Roan – red and white hairs

 Traits that arise from multiple alleles  Blood types – three alleles IA, IB, and I – four blood groups (Table 7-2)  Polygenic – traits controlled by many genes  Examples – height, weight, hair and skin color  Gene expression affected by environmental conditions  Arctic fox – temperature affects coat color