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Gregor Mendel was an Austrian Monk who is famous for his work with garden peas and his contribution to the study of heredity. Mendel noticed that sometimes the seeds of tall pea plants produced short offspring plants, and that sometimes the seeds of purple flowered plants produced white flowered offspring…. He wondered why???!!!!.... And decided to search for the answer. Seed Flower Flower Seed color color position shape Pod color Pod Plant shape height green inflated tall yellow constricted short Dominant trait round yellow purple axial (side) Recessive trait wrinkled green white terminal (tips) When he wanted to breed, or cross, one plant with another, Mendel opened the petals Remove of a flower and male parts removed the male organs. He then dusted the female organ with pollen from the plant he wished to cross it with. Pollen grains Transfer pollen Female part Male parts Cross-pollination 1. Mendel produced pure strains of pea plants by allowing the plants to self pollinate for many generations. These pure strains are called the parental or P1 generation. 2. He crossed the P1’s to get the first filial or F1 generation. Ex: Tall x Short = 100% Tall (P1) x (P1) = (F1) 3. He then crossed the F1’s with each other to get the second filial or F2 generation. P1 F1 Ex: Tall x Tall = 75% Tall, 25% short (F1) x (F1) = (F2) F2 1. The Rule of Unit Factors: Each plant had 2 factors controlling the expression of traits (One factor from each parent). 2. The Rule of Dominance Some “factors” cover, or mask, others. Dominant- masks another factor- ex. Tall Recessive- the factor that is masked- ex. Short. 3. The Law of Segregation- Pairs of factors segregate, or separate during gamete (egg or sperm) formation. Ex: Tall Plant TT (dominant) T T x x Short Plant tt (recessive) T t T t t t Meiosis- the process of making gametes (egg or sperm). When the gametes combine to form a zygote (fertilized egg), the offspring will have received one factor from each parent. t T This zygote will become a tall pea plant. T t In 1900, Walter Sutton proposed The Chromosome Theory, which linked chromosomes and meiosis to Mendel’s Laws. Today, instead of factors, we study genes. A gene is a segment of DNA on a chromosome that controls a particular hereditary trait. Because chromosomes occur in pairs, genes occur in pairs. Alternative traits of a gene are called alleles (Mendel’s factors). Gene- eye color Allele- blue, brown Genotype The genetic makeup of an organism. TT Tt tt Phenotype The appearance of an organism. Tall Short Homozygous When both alleles are the same (called pure). TT- tall tt- short Heterozygous When a pair a alleles are not the same (called hybrids). Tt- tall Probability - the likelihood that an event will occur. - # of times an event is expected______ # of times the event actually happens Ex. What is the probability that a coin toss will result in heads? ½ or 50% or 1:1 fraction percentage ratio A Monohybrid Cross- is a cross involving 1 pair of contrasting traits. Ex. What are the expected genotypic and phenotypic ratios resulting from the cross of a pure (homozygous) tall plant with a hybrid (heterozygous) tall plant? 1. Write possible genotypes and phenotypes. TT- tall Tt- tall tt- short 2. Determine parent genotypes and separate alleles (because 1 allele goes to each gamete) homozygous tall (TT) x heterozygous (Tt) tall T T T t 3. Draw a Punnett Square with 4 boxes and put the alleles from one parent on one side and the alleles form the other parent on other side. T T T t 4. Report results: Genotypic Ratio- 2 TT: 2Tt (1TT: 1Tt) Phenotypic Ratio- 4 Tall: 1 short (1 tall: 0 short)