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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
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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