Blending hypothesis Originally, organisms were thought to be a blend of their parents’...
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![Page 1: Blending hypothesis Originally, organisms were thought to be a blend of their parents’ characteristics. Pure-breeds were defined as organisms that looked.](https://reader036.fdocuments.net/reader036/viewer/2022070418/5697bfd41a28abf838cacb65/html5/thumbnails/1.jpg)
Blending hypothesis
• Originally, organisms were thought to be a blend of their parents’ characteristics.
• Pure-breeds were defined as organisms that looked identical to their parents, and they looked like their parents, etc.
• So now, using these two pieces of information, pretend you are a young scientist in the early 1800’s. You cross a purebred red flowering plant with a purebred white flowering plant. What do you expect to find?
![Page 2: Blending hypothesis Originally, organisms were thought to be a blend of their parents’ characteristics. Pure-breeds were defined as organisms that looked.](https://reader036.fdocuments.net/reader036/viewer/2022070418/5697bfd41a28abf838cacb65/html5/thumbnails/2.jpg)
THE ACTUAL RESULTS…
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Mendelian Genetics
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Father of Modern Genetics
• Austrian monk, high school teacher, and part-time garden keeper
• First to propose biological inheritance of traits
• Work not recognized until after his death
• Knew nothing about DNA
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Why pea plants?
• It’s what he had• Pea plants are true
breeding• Gregor noticed that one
stock of seed would produce only tall plants and another only short plants
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P generation
Cross-pollination
Next, Mendel wanted to find out if the recessive alleles had disappeared, orif were they still present in the F1 generation.
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VOCAB BREAK…
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• Traits• Genes• Alleles• Genotype• Phenotype
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Segregation• Mendel crossed the F1
generation with itself• He found that the
recessive traits reappeared in some of the F2 generation
• He proposed this was due to two things: the principle of dominance and segregation of alleles during formation of gametes
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Probability
• Mendel categorized and counted the many offspring of each of his experiments.
• He noticed that each time he repeated a particular cross he obtained similar results.
For example:Every time he crossed two
plants that were heterozygous for stem height (Tt), about ¾ of the offspring were tall and ¼ were short.
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Probability and Punnett Squares
• Punnett squares are used to predict this probability
• Monohybrid crosses can be performed to determine probability of genotype for one particular trait
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Genotypes
AAAa
aa
Homozygous Dominant
Heterozygous
Homozygous Recessive
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Law of Segregation• Mendel crossed the F1
generation with itself• He found that the
recessive traits reappeared in some of the F2 generation
• He proposed this was due to two things: the principle of dominance and segregation of alleles during formation of gametes
![Page 18: Blending hypothesis Originally, organisms were thought to be a blend of their parents’ characteristics. Pure-breeds were defined as organisms that looked.](https://reader036.fdocuments.net/reader036/viewer/2022070418/5697bfd41a28abf838cacb65/html5/thumbnails/18.jpg)
Law of Independent Assortment
• Genes that segregate independently do not influence each other’s inheritance