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chapter 14 weinstein

chapter 14 weinstein - 1822-1884 Gregor Mendel Gregor...

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1822-1884 Gregor Mendel Gregor Mendel, an Austrian scientist who lived and conducted much of his most important research in a Czechoslovakian monastery, established the basis of modern genetic science. He experimented on pea plants in an effort to understand how a parent passed physical traits to its offspring. After studying the data from these experiments, Mendel concluded that physical traits are passed to offspring through genetic factors called alleles. Each parent had not one but two alleles for each trait. Four alleles (two from each parent) interact to produce the final physical characteristics of an offspring. Blending versus particulate models of heredity A genetic cross Mendel was an experimentalist with a fresh approach Chose peas for his experiments, good choice: self fertilizing but could be cross fertilized 7 simple traits that bred true Followed multiple generations Quantitative approach 14.2 Mendel tracked heritable characters for three generations P- parental F 1 - first filial generation F 2 - second filial generation X = genetic cross was performed Note the 3:1 ratio in the the F 2 14.3 705 224
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Alleles, different versions of a gene There is a gene that encodes a protein that makes flowers purple (P) Another version of the gene fails to make the purple color and the flowers are white (p) P and p are different alleles of the same gene 14.4 P p Mendel’s law of segregation 14.5
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Genetic terms Dominant: P is dominant because in the hybrid F 1 (Pp) all the plants are purple Recessive: p is recessive for the same reason Homozygous: individuals with two identical alleles- true breeding (PP and pp) Heterozygous: individuals with two different alleles- will not breed true (Pp) Genotype: genetic make up of an individual Phenotype: appearance of an individual Individuals with the same phenotype can have different genotypes Pp and PP are both purple they have the same phenotype But they have a different genetic make up: Pp is a heterozygote and PP is a homozygote Genotype ratio is different than the phenotype ratio 14.6 A test cross- how to determine the genotype of an individual 14.7 Mendel’s law of independent assortment Dihybrid cross Two traits yellow/green (Y/y) and round/wrinkled (R/r) F1 self-pollinated
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