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Punnett Squares & Probability
What is probability?
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Probability What is probability?
The likelihood that a particular event will occur The principles of probability can be used to predict the outcomes of genetic crosses.
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Punnett Squares The gene combinations that might result from a genetic cross can be determined by drawing a diagram
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Tt X Tt Cross Section 11-2 Go to Section:
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Allele combinations Homozygous: organisms that have two identical (same) alleles = true-breeding for a particular trait TT tt Heterozygous: organisms that have two different alleles = hybrids for a particular trait Tt
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Phenotype: visible, physical characteristics
Tall or short Genotype: not visible, genetic makeup Homozygous or heterozygous
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Independent Assortment
Does the gene that determines whether a seed is round or wrinkled in shape have anything to do with the gene for seed color? NO!!! The alleles for seed shape and seed color in pea plants do not influence each other’s inheritance
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The Principle of Independent Assortment
Genes for different traits can segregate independently during the formation of gametes.
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Summary of Mendel’s Principles
Inheritance is determined by genes passed from parents to offspring Some forms of genes are dominant and others are recessive Each offspring has two copies of a gene (alleles), one from each parent because they are segregated during gamete formation The allele for different genes usually segregate independently of one another
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What will happen if some alleles are neither dominant nor recessive?
What will happen if some traits are controlled by more than one gene?
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Incomplete Dominance When one allele is not completely dominant over another For example: 4 o’clock plant
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Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
Section 11-3 Go to Section:
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Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
Section 11-3 Go to Section:
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Codominance Both alleles contribute to the phenotype of the organism
For example: roan
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