Probability  The principles of probability can be used to predict the outcomes of genetic crosses  Think of probability like flipping a coin. If you flip a coin 3 times in a row, what is the probability you will get heads 3 times?  ½ X ½ X ½ = 1/8

The Punnett SquareThe Punnett Square Tall Pea Plant (P Generation) Short Pea Plant (P Generation) Genotype Results: 100% Tt (Hybrid/heterozygous) Phenotype Results: 100% Tall Punnett squares are used to figure out the probability of a genetic cross

Two-Factor Cross: F1

Two-Factor Cross: F2  Crossed  Heterozygous F1 plants (RrYy) with each other to determine if the alleles would segregate in the F2 generation.  RrYy × RrYy  Produced  9:3:3:1 ratio

The Principle of Independent Assortment  Independent Assortment:  Genes for different traits can segregate independently during the formation of gametes.  Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

Independent Assortment  Two-Factor Cross  Mendel determine if the segregation of one pair of alleles affects the segregation of another pair of alleles  Two-Factor Cross: F1  Crossed true-breeding plants  Round yellow peas (genotype RRYY ) X wrinkled green peas (genotype rryy ).  F1 Offspring  All round yellow peas ( RrYy ).

Pedigrees Can Be Used to Study How Traits Are Inherited  Pedigree:  A family history that shows how a trait is inherited over several generations.  Ex: Albinism  Sex-linked trait:  A trait whose allele is located on the X chromosome.  Usually recessive  Males usually exhibit the sex-linked condition  Ex: Color blindness

Incomplete Dominance  Incomplete Dominance:  One allele is not completely dominant over another  The heterozygous phenotype is somewhere in between the two homozygous phenotypes.  Example: Pink flowers

Codominance  Codominance:  Both alleles contribute to the phenotype.  Example:  Chickens  The allele for black feathers is codomiant with the allele for white feathers  Roan Cow  The allele for white hair is codominant with the allele for red hair

Multiple Alleles  Multiple Alleles:  Genes that are controlled by more than two alleles.  Example:  Rabbits  A rabbit's coat color is determined by a single gene that has at least four different alleles.

Polygenic Traits  Polygenic Traits:  Traits controlled by two or more genes  Example:  Human Skin  Skin color in humans is a polygenic trait controlled by more than four different genes.