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Mendel AUSTRIAN MONK AND FATHER OF GENETICS 1822-1884 Genetics Vocabulary • Genetics: the study of how genes/traits are passed from parents to offspring •Heredity: transmission of characteristics from parent to offspring Genetics Vocabulary • Probability: likelihood an event will happen and can be expressed as percentages, fractions, or decimals Probability = # of times an event is expected to occur number of chances for the event to occur Probability EX. There is a large cage filled with 225 Black mice AND 25 white mice. There is a total of 250 mice. What is the probability of catching a white mouse? Probability EX. 225 Black mice AND 25 white mice Total number of mice was 250 Probability (of getting a white mouse)= 25/250 = = 0.10 OR 10% Mendel’s Work Mendel Mendel’s Peas • Observed 7 characteristics • Observed 2 contrasting traits within each characteristic EX. CHARACTERISTIC: flower color TRAIT: White or purple Why peas? 1. 7 easy to observe characteristics 2. Each trait only had 2 choices (ex: tall vs. short, yellow vs. green seeds) 3. Reproduce quickly 4. Self-fertilization: pollen from the anther (male part) will fertilize the pistil (female part) of the same flower 5. Cross-pollination: uses the pollen from one plant to fertilize the female gamete (in the pistil) on another other plant. Mendel’s Experiment Step One ◦ Self-pollinated white flowers with white flowers for many generations ◦ Self-pollinated purple flowers for many generations ensures he has created pure traits ◦ These flowers are called the P1 generation Mendel’s Experiment, cont. Step Two ◦ Cross-pollinated a purple flower and white flower from the P1 generation ◦ Resulting plants (first filial F1 generation) ALL had purple flowers Mendel’s Experiment, cont. Step Three ◦ Cross-pollinated the F1 generation ◦ Resulting plants (F2 generation) had many purple flowers and a few white flowers Trait for white had been “hidden” in the F1 generation, it did not disappear. Summary of Mendel’s Experiment P1 Generation Purple flowers X P1 Generation White flowers F1 Generation Purple flowers F2 Generation Purple flowers (705) White flowers (224) Self-pollination Mendel’s Results and Conclusions • He began to observe patterns- Each cross yielded similar ratios in F2 generation (3/4 had purple, and 1/4 white: a 3:1 ratio) • Recessive and Dominant Traits ◦ Dominant traits masked recessive traits ◦ Example: Purple color was dominant to white since it “masked” the white color. Mendel’s Results • Gene ( DNA located on a chromosome) codes for a characteristic (ie flower color) • Different forms of a gene = allele (purple or white) • Letters used to represent alleles dominant trait capitalized (purple = P) recessive lower case (white = p) Genotypes and Phenotypes • Genotype: alleles an organism inherits EX: PP Pp pp • Phenotypes: physical appearance due to the genotype EX: PP (purple) Pp (purple) pp (white) Trick to remember what theses mean: Genotype =gene Phenotype=physical Homozygous vs. Heterozygous • Homozygous: both alleles are alike (PP or pp) • Heterozygous: alleles are different (Pp) Remember: homo= same Hetero= different Mendel’s Laws Law of segregation: paired chromosomes separate during meiosis (formation of gametes) Mendel’s Laws Law of Independent Assortment: alleles sort independently of one another (not all dominant appeared together)
