Gregor Mendel ( )  Monk, teacher, scientist, & gardener.  Experimented with pea plants.  Observed and recorded information for 8 years on over 32,000 plants.  Discovered some of the basic laws of heredity.  Heredity-passing of traits from parent to offspring.  Presentation to the Science Society in1866 went unnoticed.  He died in 1884 with his work still unnoticed. His work rediscovered in  Known as the “Father of Genetics”.  Discovered all this before we even knew what genes (DNA) were.

Mendel’s Peas  In peas, many traits (factors) appear in two pure forms (i.e. tall or short, round or wrinkled, yellow or green.)  The flower is the reproductive organ, and the male and female are both in the same flower.  He crossed 2 pure strains by putting the pollen (male gamete) from one purebred pea plant on the pistil (female organ) of another purebred pea plant to form a hybrid or crossbred.

Mendel’s Peas (seven pure traits he studied)

Mendel’s Experiments  He experiments with pure traits in his parent generations.  He experimentally crosses different pure strains to develop hybrids (offspring).  He then crossed the hybrids and analyzed the results(offspring =grandchildren).

Mendel’s Observations  He noticed that peas are easy to breed for pure traits, and he called the pure strains purebreds.  Purebreds-breeding of pure traits(not mixed, tall w/tall or green w/green).  He developed pure strains of peas for seven different traits (i.e. tall or short, round or wrinkled, yellow or green, etc.)  He crossed these pure strains to produce hybrids.  Hybrids-crossbreed of traits (mixed traits, tall w/short).

Mendel’s Results Mendel crossed purebred tall plants with purebred short plants and the first generation plants were all tall. Parent Generation to First generation : Purebred: Cross tall w/tall=tall Hybrid: Cross tall w/ short=tall When these tall offspring were crossed the result was a ratio of 3 tall to 1 short. First Generation to Second Generation (hidden genetic material): Hybrids: Cross tall w/ tall =3 tall and 1 short (ratio of 3 to 1)

Mendel’s Results Continued: Dominant Traits RULE  Strong hereditary traits hide weak traits.  Mendel called stronger traits –DOMINANT Traits (strong characteristic that is usually visible to the eye, and covers/hides weaker traits)  Mendel called weaker traits –RECESSIVE Traits (weak characteristic that gets covered/hidden by dominant traits, usually not visible to the eye, but hidden in the DNA)

Mendel’s Results Continued:  Dominant traits=capital letters (T)  Example: TT=tall Tt=tall  Recessive traits=lower case letters (t).  Example: tt=short  Homozygous=purebred/pure (matching traits) TT or tt  Heterozygous=hybrid (mixed traits) Tt

Summary of Mendel’s Laws  1. Law of Dominance-pure parents=pure traits and hybrid parents=dominant appearance (dominant traits cover up recessive traits)  2. Law of Segregation-alleles separate (sex cells) and recombine at fertilization (explanation for hybrids having a different appearance from their parents-short parents w/tall kids (hidden genes)  3. Law of Independent Assortment-alleles for traits are distributed independently of one another (tall gene won’t affect color gene, disproved later)

What IF?  Mendel was able to create these laws without modern technology.  He observed the phenotype (appearance) without even knowing about genotype (genes/DNA).  He still was able to deduce/infer that the genetic material was there.  These same laws are now known to apply to people.  Traits/genes determine who we are and what we look and act like.  Amazing!

 American geneticist and embryologist  Modeled all of his experiments after Mendel  Used fruit flies  Picked identifiable traits (eye color)  Proved Mendel’s law of independent assortment wrong  Red eyed flies and then white eyed flies showed up  Figured out genes/chromosomes without knowing DNA  Figured out that it was sex-linked trait- tied to the male (Y) or female chromosome (X)  Easier for the recessive phenotype-appearance to appear (sex-linked if X)  CHROMOSOME THEORY OF HEREDITY- 1. Genes are inside chromosomes in a certain spot. 2. Fragments cross over between matching up pieces of chromosomes 3. Frequency of crossover tied to how far apart in the nucleus Thomas Morgan

Reginald Punnett ( )  British geneticist  Published Mendelism in 1905  First textbook on genetics  First book for the public on genetics  Created the Punnett Square- tool used to predict the probability of inheriting traits (possible genotypes-gene codes- and phenotypes-physical appearance )