Chapter 11 Gregor Mendel
Gregor Mendel’s Life (1822-1884) • Born in Austria (now Czechoslovakia) in 1822 • Only son of a peasant farmer. • Entered the monastery in 1843 to avoid a life of poverty. • Ordained a priest in 1847. • Monastery a center for teaching and scientific research. Taught math, physics, and Greek • Studied at the University of Vienna. Did not do well.
Returned to monastery in 1853; considered a failure. • Interested in selective breeding for favorable traits. • Choose to work with peas. (Pisumsativum) • First to collect mathematical data. • His published work was ignored by other scientists. • In 1868, elected Abbot of his Monastery.
His work stored at the monastery was burned after his death in 1884. • Forgotten until his work was rediscovered in 1900. • Today he is known as the Father of Genetics
Gregor Mendel carried out the first important studies of heredity, the passing on of characteristics from parent to offspring. • Characteristics that are inherited are called traits. • Predicted how traits are transferred from one generation to the next. First scientist to record data and use mathematical calculations.
Pea Plants • Garden peas reproduce sexually. • Have male (pollen) and female (egg or ovule) gametes. • Pollination is the transfer of pollen to the female organ. • Fertilization occurs when the pollen and egg fuse together. • The fertilized ovule matures into a seed.
Making a cross • Mendel transferred pollen from one plant to another plant with different traits.
Monohybrid Cross • Bred tall plants to be tall for many generations – called pure. • Bred short plants to be short for many generations – called pure. • Crossed pure tall and pure short. • 100% of offspring were tall. Parent generation F1 generation
Mendel crossed two of the F1 generation. • ¾ of offspring were tall. • ¼ offspring were short. • This generation called the F2. • Mendel did this same experiment with 7 other traits.
Mendel concluded that each organism has two factors for each of its traits. • We now call these factors genes. • Alternative forms of genes are called alleles. • Alleles are located on the chromosomes – one from mother and one from father.
Dominant and Recessive • Traits are dominant or recessive. • When an organism has two different alleles, the one that is observed is called dominant. • The trait that is hidden is called recessive. • Recessive is only seen if both alleles are recessive.
The Law of Segregation • The two alleles for each trait must separate when the gametes are formed. • A parent passes on only one of its two alleles to the offspring.
Capital letter = Dominant alleleSmall letter = Recessive allele • Two organisms can look alike but have different alleles. (TT or Tt) • The way an organism looks is called its phenotype. • The actual genes (alleles) an organism has is called its genotype.
Homo or Hetero • An organism is homozygous if both alleles are the same. • TT = homozygous dominant • tt = homozygous recessive. • An organism is heterozygous if the alleles are different. • Tt = heterozygous or hybrid.
Punnett Square • In 1905, Reginald Punnett created a short-hand way to determine the expected proportions of possible genotypes. • Called a Punnett Square
The capital letter, or dominant trait, should be written before the lower case, recessive trait.
Law of Independent Assortment • Genes for different traits are inherited independently of each other. • That means that traits like height and seed color are not linked together.
Dihybrid Cross • A cross involving two traits is called a dihybridcross. • The traits are independently assorted.
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