CHAPTER 9 - GENETICS 9-2: GENETIC CROSSES 9-1: FUNDAMENTALS OF GENETICS

GENETICS GENETICS –field of Biology devoted to understanding how characteristics are transmitted from parents to offspring

Gregor Mendel Austrian monk Austrian monk Studied math + science at college Studied math + science at college Studied heredity Studied heredity –The transmission of characteristics from parents to offspring Studied pea plants Studied pea plants –Pisum sativum Known as the “Father of Genetics” Known as the “Father of Genetics”

Mendel’s Garden Peas Observed 7 characteristics of pea plants Observed 7 characteristics of pea plants Each characteristic occurred in 2 contrasting traits Each characteristic occurred in 2 contrasting traits

Peas (cont.) After planting the seeds and allowing them to grow, he noticed that purple- flowering plants grew from purple- flowering plant seeds, but he also noticed that white -flowering plants also grew from purple-flowering plants After planting the seeds and allowing them to grow, he noticed that purple- flowering plants grew from purple- flowering plant seeds, but he also noticed that white -flowering plants also grew from purple-flowering plants He also noticed that TALL plants grew from TALL seeds, but also short plants grew from TALL seeds. He also noticed that TALL plants grew from TALL seeds, but also short plants grew from TALL seeds. WHAT WAS HAPPENING???? WHAT WAS HAPPENING????

Mendel’s Methods Mendel carefully controlled the traits for each generation through pollination Mendel carefully controlled the traits for each generation through pollination –Pollen grains from male (anther) transferred to female (stigma)

Other types of pollination Self-pollination Self-pollination –Pollen is transferred from the anther of a flower to stigma of same flower or flower on same plant Cross-pollination Cross-pollination –Flowers of two separate plants

Mendel’s Experiments Plants that are PURE for a trait always produce offspring with that trait Plants that are PURE for a trait always produce offspring with that trait –Pure (AKA “strain”) –Ex. Pure yellow pods self-pollinate produce yellow pod offspring The term true-breeding denotes plants that are pure for a specific trait The term true-breeding denotes plants that are pure for a specific trait How did Mendel produce these strains? How did Mendel produce these strains? –Allowed pure plants to self-pollinate for several generations (lifetime of a plant)

Mendel’s experiments (cont.) He collected a total of 14 strains, one for each trait he observed He collected a total of 14 strains, one for each trait he observed These strains were called the Parental generation, or P generation These strains were called the Parental generation, or P generation He then cross-pollinated each of these strains. The offspring produced were called the 1 st Filial generation, or F 1 generation He then cross-pollinated each of these strains. The offspring produced were called the 1 st Filial generation, or F 1 generation

Mendel’s experiments (cont.) He then allowed one F 1 plants to self- pollinate themselves and the offspring were called the 2 nd Filial generation, or F 2 generation He then allowed one F 1 plants to self- pollinate themselves and the offspring were called the 2 nd Filial generation, or F 2 generation

TABLE 9-1, P.176

Mendel’s Results + Conclusions In one experiment, Mendel crossed a pure green pod plant with a pure yellow pod plant. In his F 1 generation, he found that all had green pods. In one experiment, Mendel crossed a pure green pod plant with a pure yellow pod plant. In his F 1 generation, he found that all had green pods.

Results (cont.) He allowed his F 1 generation to self- pollinate, and found that ¾ of the F 2 plants had green pods and ¼ had yellow pods. He allowed his F 1 generation to self- pollinate, and found that ¾ of the F 2 plants had green pods and ¼ had yellow pods.

Results (cont.) These observations led Mendel to believe that there were FACTORS that controlled what trait would be shown These observations led Mendel to believe that there were FACTORS that controlled what trait would be shown –Also concluded that a pair of factors* determined the trait  b/c of the alternate forms of a trait*

Dominant & Recessive Whenever Mendel crossed strains, on of the P 1 traits failed to appear in the F 1 plant. In every case, the trait reappeared in a 3:1 ratio in the F 2 generation Whenever Mendel crossed strains, on of the P 1 traits failed to appear in the F 1 plant. In every case, the trait reappeared in a 3:1 ratio in the F 2 generation He hypothesized that there was one DOMINANT factor that masked the other factor a specific trait. He hypothesized that there was one DOMINANT factor that masked the other factor a specific trait. He called the other factor recessive He called the other factor recessive –Not seen in an organism when paired with dominant factor

Law of Segregation A pair of factors is segregated, or separated, during the formation of gametes A pair of factors is segregated, or separated, during the formation of gametes

Law of Independent Assortment Factors for different characteristics are distributed to gametes independently Factors for different characteristics are distributed to gametes independently –Do not always get both dominant factors together –Occurs because of Meiosis

Chromosomes + Genes What Mendel did in his research was pave the way for a new branch of science called Molecular Genetics What Mendel did in his research was pave the way for a new branch of science called Molecular Genetics –Study of structure + function of chromosomes and genes –Genes are codes for specific traits –An alternate form of a gene is called an allele  Alleles are what Mendel called factors –Dominant – capital letter (D) –Recessive – lower case letter (d)  Is only observed for genes located on separate chromosomes or located far apart on the same chromosome