Lecture 3 - Lecture 3 Mendels Laws and Single gene...

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Lecture 3 Mendels Laws and Single gene inheritance
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Mendel’s first law: The law of equal segregation. Between 1856 and 1863, he cultivated and tested some 29,000 pea plants. The two members of a gene pair (alleles) segregate from each other during meiosis; each gamete has an equal probability of obtaining either member of the gene pair Gregor Mendel
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Terminology Zygote: a fertilized egg, the first cell that develops into progeny individual Homozygote: an individual with a pair of identical alleles Heterozygote: an individual in which the alleles differ Monohybrid: refers to an individual heterozygous for one gene Individuals may be classified as… •Homozygous dominant : both alleles dominant (Y/Y) •Heterozygous: one dominant and one recessive (Y/y) •Homozygous recessive: both alleles recessive (y/y) …at a given locus Genotypes: allelic combinations that underlie phenotypes
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The seven phenotypic pairs studied by Mendel
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Cross-pollination and selfing are two types of crosses
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Mendel’s crosses resulted in specific phenotypic ratios
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Figure 2-12 part 1 A single-gene model explains Mendel’s ratios
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Figure 2-12 part 2 A single-gene model explains Mendel’s ratios
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Figure 2-12 part 3 A single-gene model explains Mendel’s ratios
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A single-gene model explains Mendel’s ratios Pure Phenotype 3:1 Phenotype 1:1
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Do you think Mendel was lucky? More likely, he screened a great many more traits that did not conform to these patterns!
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Genotype (1:2:1) Phenotype (3:1) ¼ Y/Y ½ Y/y ¼ y/y ¾ yellow ¼ green Crossing the F1 plants, where Y/y is crossed with Y/y is called a monohybrid cross. Equal segregation of the alleles results in the 3:1 ratio…in terms of phenotype! the
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