patterns of inheritance. ancestry and obesity in the news
TRANSCRIPT
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Patterns of InheritancePatterns of Inheritance
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Ancestry and ObesityIn The News
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Historical Views of Inheritance
• Hippocrates (~ 400 B.C.) – Particles given off from bodies
of father and mother– Offspring was mixture
• Homunculus (pre-1900) – Each sperm contained a tiny
preformed human
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Gregor Mendel
• Austrian Monk
• Worked with garden peas
• Discovered process of heredity
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Suitability for Using Peas• Each flower has male & female parts
• Sex organs are enclosed & protected
• Pollination can be controlled
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True-breeding• Generations of self-fertilization produce
consistent offspring
• Mendel used true-breeding varieties
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Mendel’s Experiments• Artificially crossed true-breeding plants
• Recorded offspring from cross-fertilization
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Characters Used by Mendel
• 7 true-breeding traits
• Monohybrid crosses
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Mendel’s Crosses• Example:
– Tall plant crossed with short plant
– Hybrid offspring (F1) were not intermediate
– Resembled only one parent
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F1 of Hybrid Cross
• Dominant – form expressed in F1
• Recessive – form not expressed in F1
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Mendel’s Next Step• Allowed F1 to self fertilize
• F2 expressed dominant & recessive forms
• Ratio in F2 = 3:1 (dominant:recessive)
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Mendel’s Monohybrid Crosses
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Conclusions of Mendel’s Work
• Traits are inherited as genes
• Alleles are alternate forms of genes
• Gametes receive only 1 allele of each pair
• Alleles may differ or may be identical
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Mendel’s Law of Segregation
Each gamete receives only one of an organisms pair of alleles, and which one it receives is determined by chance
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Alleles of an Individual• Homozygous – identical alleles for a trait
• Heterozygous – different alleles for a trait
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Genotype• An organisms allelic makeup• Dominant designated by capital letter• Recessive designated by small letter
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Phenotype• Expression of alleles• Dominant gene is expressed if present
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Punnet Square
• Diagram to predict possible combinations
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Test Cross Determining Genotype
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Dihybrid CrossesAre Traits Linked?
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Law of Independent AssortmentThe transmission of alleles for one trait into gametes does
not affect the transmission of alleles for other traits
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Location of Mendel’s Factors
• Mendel did not know where traits were located
• Chromosomes were discovered 22 years after Mendel’s work was published
• Walter Sutton suggested that Mendel’s factors were on chromosomes
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Thomas Hunt Morgan• Studied fruit flies, Drosophila melanogaster• Discovered different traits in flies• Experiments to test Mendelian inheritance
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Morgan’s Cross• White-eyed male
• Red-eyed female (normal eye color)
• Eye color followed Mendel’s 3:1 ratio
• However, all white-eyed F2 were males
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Conclusion of Morgan’s Experiment
• White eyes were linked to males
• Trait was found on X chromosome
• Females have two X chromosomes
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Conclusion of Morgan’s Experiment
• Traits are located on chromosomes
• Some traits are sex-linked
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End chapter 13