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Transcript
Chapter: 9 Fundamentals of Genetics Objectives Describe how Mendel was able to control how his pea plants were pollinated. Describe the steps in Mendel’s experiments on truebreeding garden peas. Distinguish between dominant and recessive traits. State two laws of heredity that were developed from Mendel’s work. Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes. I. Father of Genetics A. Gregor Mendel Austrian Monk B. Knowledge of statistics helped him with heredity A. A. Heredity = the transmission of characteristics from parents to offspring. II. Mendel’s Legacy A. Observed 7 traits (a genetically determined variant of a characteristic) of Garder Peas A. B. C. D. E. F. G. Height Flower position Pod color Pod appearance Seed texture Seed color Flower color III. Mendel’s Methods A. Pollination Male parts combine with female parts in plants B. Self-pollination = male parts combine with female parts of same plants C. Cross pollination = male parts combine with female parts of different plants A. IV. Mendel’s Experiments A. Crossed the P generation A. These were plants that each had a specific traits (ex: purple flowers and white flowers) B. Mendel got his first F generation A. B. He used the symbol F1 All flowers were purple C. Mendel then crossed two from F1 generation to get F2 generation. A. He got 3 purple flowers and 1 white flowers. V. Mendel’s Results A. B. Traits were observed based on dominant factors and recessive factors. Dominant factor – the trait that appears even if a recessive trait is present A. B. C. Recessive factor – can only be observed when it is paired with another recessive factor A. B. D. Always shown as a capital letter B Always shown as a lowercase letter b The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait. VI. Law of Segregation A. Factors that control traits are separated during the formation of gametes. VII. Law of Independent Assortment A. Dominant factors of one trait are not always paired with dominant factors of different traits. A. Ex: You could be dominant for seed color but recessive for flower color VIII. Support for Mendel’s Conclusions We now know that the factors that Mendel studied are alleles, or alternative forms of a gene. One allele for each trait is passed from each parent to the offspring. IX. Genetic Crosses A. Genotype – an organism’s genetic make up. A. The letters (BB, Bb, or b,b) B. Phenotype – the appearance of the trait A. Ex. Purple flowers C. Probability – likelihood a specific event will occur A. A probability may be expressed as a decimal, a percentage, or a fraction. X. Predicting Results of Monohybrid Crosses A. Cross in which only 1 characteristic is tracked. B. A Punnett square can be used to predict the outcome of genetic crosses. C. Homozygous – same genotype alleles Ex. BB or bb D. Heterozygous – one dominant allele and one recessive allele Ex. Bb XI. Homozygous dominant x Homozygous recessive Purple is dominant over white PP (purple) x pp (white) p p Genotypic ratio = 4:0 P P p P P p P p P p Phenotypic ratio = 4 purple : 0 white XII. Homozygous dominant x heterozygous Purple is dominant over white PP (purple) x Pp (purple) P p p Genotypic ratio = 2:2 P P P P P P P p P p Phenotypic ratio = 4 purple : 0 white XIII. heterozygous x heterozygous Purple is dominant over white Pp (purple) x Pp (purple) p P Genotypic ratio = 1:3:1 P P P p P p P p p p Phenotypic ratio = 3 purple : 1 white XIV. Incomplete dominance In roses (R = red, Rr = pink, rr = white) r R Genotypic ratio = 1:3:1 R P r R R R r R r r r Phenotypic ratio = 1 red: 2 pink: 2 white XV. Co-Dominance In guinea pigs (B = black, Bb = black and white, bb = white)