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Mendelian Genetics. Mendel studied 7 traits He studied one trait at a time He began his work by breeding together two True Breeding plants. A True Breeding plant self-pollinates and always has offspring that share its traits.
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Mendelian Genetics • Mendel studied 7 traits • He studied one trait at a time • He began his work by breeding together two True Breeding plants. • A True Breeding plant self-pollinates and always has offspring that share its traits. • Example: Tall plants always produce tall plants. Short plants always produce short plants.
Mendel’s Experiments • Mendel asked, “What happens if I cross a true breeding tall plant with a true breeding short plant?” • _____________________________________ According to the theory of blending, what will be the results of this cross? Medium tall plants
Mendel’s Results • What were the ACTUAL results of a cross between a true breeding tall and a true breeding short plant? • All of the offspring were TALL. • True breeding plants are the • Parents or P generation • The offspring of the P generation are the • First Filial (filial = son in Latin) or F1 generation
How did Mendel conduct his Experiment? • Flower Worksheet ♂= male ♀=female
Mendel’s Experiment • Mendel removed the stamen (♂) from the flower of a TALL plant. The stamen is made of the anther (covered in pollen) and the filament. • He then removed pollen from the anther and brushed it on the stigma (♀) of the flower of a SHORT plant.
Mendel’s Results • The plants produced seeds. • The seeds were planted • Every seed produced a TALL plant • Mendel’s First Conclusion: biological inheritance is determined by factors that are passed from one generation to the next. • Today we know these factors as genes. F1 generation P generation
Mendel’s Second Experiment • Mendel crossed plants from the F1 generation together. • He created thousands of crosses this way. • Each flower produced seeds. • Thousands of these seeds were planted and grew into the F2 generation.
Mendel’s Results of the F1 Cross • Mendel observed the thousands of plants he grew from seeds. • He found the missing trait had reappeared!! • Among the new F2 generation there was a 3:1 ratio of Tall to Short Plants P generation F1 generation F2 Generation
Mendel’s Second Conclusion • Second Conclusion: Principle of dominance – Some alleles are dominant and some are recessive. An organism with one or two dominant alleles for a particular form of a trait will have that form (tall plant). • An organism with two recessive forms of a trait will have that form (short plant). ********************** • An organism inherits TWO alleles for every trait. One from its mother and one from its father.
Rules for Genetic Problems • Two alleles for a gene are represented with the same letter. • Dominant alleles are represented with an uppercase letter, and recessive alleles are represented with a lower case letter. • Example: Tall allele = T; Short allele = t • Example: Round seeds = R; Wrinkled seeds =r • The letter representing the gene is usually the first letter of the dominant trait.
Rules for Genetic Problems • Try this: • A pea plant has two alleles for seed color. • Yellow is the dominant seed color • Green is the recessive seed color. • What is the symbol for yellow seed color?_____________ • What is the symbol for green seed color? _____________ Y y
Rules for Genetic Problems • Since a plant inherits two alleles for seed color it may inherit any of the following genetic combinations • YY = yellow seeded plant • Yy = yellow seeded plant • yy = green seeded plant. • Remember: A recessive trait appears only when an organism inherits two recessive alleles!
More Vocabulary • Homozygous genes = same alleles for the trait (YY, yy) = pure • Heterozygous genes = different alleles for the trait (Yy) = hybrid • Genotype = genetic make-up of an organism. • Phenotype = physical characteristic of an organism.
Punnett Squares • Named after R.C. Punnett, British geneticist, 1875-1967 • Used to understand the probability of the outcome of a genetic cross.
Practice • Cross 1 - Make a Punnett Square of a cross between the P generation of a yellow seeded plant (YY) and the F1 generation (Yy) • Cross 2 - Make a Punnett Square of a cross between the P generation of a green seeded plant (yy) and the F1 generation (Yy) • What is the phenotype and genotype for the offspring in cross 1? Cross 2?
