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Mendel and the Gene Notes

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Biological Sciences
BIOSC 0160
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1/23 Chapter 13: Mendel and the Gene Heredity • Concept o Offspring resemble parents o Offspring are virtually identical to asexual parents (barring mutation/environmental influences) o Offspring are similar to parent in sexual reproduction o Basis: inherited genetic information • State of Understanding in 1850 o Merely that offspring resemble parents; mechanism was not known o Darwin: Is heredity “blending”? o DNA discovered as hereditary material around 1952-1953 • Distinction between Heredity and Reproduction o Heredity is the hallmark of life o Heredity is more than mere replication; also involves resemblance o i.e. fire can reproduce, but it cannot pass on genetic information (Dawkins) Mendel • Gregor Mendel o “Founder” of genetics o Published in 1865 • Experiments o Worked with peas  Ideal for research because of differences in varieties and attributes 1/23  Bred varieties and offspring in controlled experiments o Quantitative  Considered pattern in numbers of offspring crosses; central approach Genetic Experiments • True Breeding Varieties o Parents with a certain trait that always yield offspring with the same trait o Character: attribute (flower color) o Trait: form of the character (purple) • Monohybrid Cross o “Mono”=one character; “Hybrid”: cross between different true-breeding varieties 1. P-generation: true-breeding parents (one white, one purple) 2. Breed (cross) varieties 3. Count resulting F 1filial 1) offspring a. How many have white flowers? b. How many have purple flowers? c. Result: all 1 have purple flowers 4. Cross F a1d count a. 705 purple-flowered in F 2 b. 224 white-flowered in F2 o Interpretation  Heritable factor (gene) is present in alternate forms (alleles)  Each offspring inherits two alleles for a character, one from each parent • One is dominant, one is recessive • Alleles segregate during gamete production (metaphase I) o Vocabulary 1/23  Homozygous: identical alleles  Heterozygous: two different alleles  Phenotype: appearance  Genotype: genetic make-up o Punnett Square • Test Cross o Used to determine genotype of a known phenotype o Done by breeding with a true-breeding white-flowered plant o Interpretation  PP x pp All purple  Pp x pp Half purple, half white • Dhybrid Cross o “Di”=two; “Hybrid”=cross between t
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