 Genetics is the study of how traits are passed from parents to offspring.  Heredity is the actual passing of traits from parents to offspring.

 Gregor Mendel is known as the father of modern genetics.  Experimented with pea plants

 Because of Mendel’s experiments we now know that inherited traits are controlled by different versions of genes known as alleles.  Alleles can be dominant or recessive. ◦ Dominant alleles can hide alleles for other traits. Use capital letters to represent them. ◦ Recessive alleles can be hidden by alleles for other traits. Use lower case letters to represent them.

 The results of most of Mendel’s experiments looked the same.  The F1 generation showed all of the dominant traits, while the F2 generation showed the dominant and recessive traits in a ratio of 3:1.

 Phenotype—an organism’s appearance (word description)  Genotype—an organism’s genetic make-up (letter code) ◦ Genotype for purple flowers: PP or Pp ◦ Genotype for white flower: pp

 Homozygous—both alleles are the same (pure) PP or pp  Heterozygous—two alleles are different (hybrid) Pp

 Monohybrid Crosses —only one characteristic is tracked  A tool used to predict the outcome of different types of monohybrid crosses is called a Punnett Square ◦ Example: TT x tt ( Pure tall plants x Pure short plants) TT t t Result: 100% Heterozygous tall offspring Genotype = Tt Phenotype = tall Tt

 Incomplete Dominance occurs when offspring have a phenotype that is in between that of the two parents. RRRr rr

 Punnett Squares for incomplete dominance are completed in the same manner. Except that the heterozygous individuals will have the blended phenotype.  Example: Pink Flower x Pink Flower Rr x Rr Rr R r RRRr rr Results: 25% Red flowers 50% Pink flowers 25% White flowers Genotypic Ratio: 1 RR : 2 Rr : 1 rr Phenotypic Ratio: 1 Red : 2 Pink : 1 White

 Codominance occurs when both alleles in a pair are expressed but do not actually blend.  Human Blood Type is an example of codominance.  Three alleles (A,B and O) are involved in determining blood type. However, you still only inherit two (one from mom and one from dad) ◦ A and B are both dominant; O is recessive ◦ Type AB blood has one genotype: AB ◦ Type A blood has two possible genotypes: AA and AO ◦ Type B blood has two possible genotypes: BB and BO ◦ Type O blood has only one possible genotype: OO

 Dihybrid Cross --shows two traits at the same time.  Example: RrYy x RrYy (heterozygous round and yellow seeds) R = round r = wrinkled Y = yellow y = green RYRyrYry RY Ry rY ry RRYYRRYyRrYYRrYy RRYyRRyyRrYyRryy RrYYRrYyrrYYrrYy RrYyRryyrrYyrryy Results: 9 round/yellow 3 round/green 3 wrinkled/yellow 1 wrinkled/green