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