Gregor Mendel w “The Father of Genetics” w Studied peas: easy and quick to breed, can control mating

Mendel’s Pea Plants Plant Height Tall Short Pod color Seed Shape Pod Shape Seed Color GreenYellow GreenYellow RoundWrinkled SmoothPinched

Mendel’s Experiments Mendel mated “purebred” plants. (Homozygous) Offspring always looked like parents. X Purebred Short Parents Purebred Tall Parents X Short Offspring Tall Offspring

Mendel’s First Experiment Mendel crossed purebred plants with opposite forms of a trait (like tall x short). Called parental generation, or P generation. Parent Tall P generation Parent Short P generation X Offspring Tall F1 generation All of the offspring grew to be tall plants. None resembled the short parent. He called this generation of offspring the first filial, or F1 generation, (The word filial means “son” in Latin.)

Mendel’s Second Experiment Mendel then crossed two of the offspring from the F1 generation in his first experiment. Tall F1 generation X 3⁄4 Tall & 1⁄4 Short F2 generation Mendel called this second generation of plants the second filial, F2, generation. It had both tall and short plants in a 3:1 ratio Parent PlantsOffspring

TT Tt tt T t T t Genotype: Tt x Tt 1 TT, 2 Tt, 1 tt

Mendel’s Law of Segregation Traits exist in different forms and one individual contains 2 factors (alleles) for each trait. When egg or sperm are formed, the two alleles separate (segregate) so only one factor is passed down -- at random.

Dominant and Recessive Genes Mendel concluded that one factor masked the other factor. Alleles that mask or hide other alleles, such as the “tall” allele, are said to be dominant. A recessive allele, such as the short allele, is masked, or covered up, whenever the dominant allele is present.

What happens if you cross plants heterozygous for 2 traits? Green AlleleYellow Allele Round seed Allele Wrinkled seed allele Yellow seeds are dominant over green and round seeds are dominant over wrinkled seeds. X X

Law of Independent Assortment Each pair of alleles separate independently of each other in the production of eggs and sperm. The process is random for each— So if there are 4 possible outcomes in a monohybrid cross (cross of heterozygotes for 1 trait) There are 4 x 4 = 16 possible outcomes in a dihybrid cross (cross of heterozygotes for 2 traits)

Most traits are not so simple w Incomplete dominance A heterozygous individual has an intermediate phenotype

Codominance w Characteristics of both traits show up in the phenotype

Multiple Alleles w Each allele at multiple sites contributes to a phenotype

THE END