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11-2 Probability and Punnett Squares

Sexual Reproduction and Genetics. Chapter 10. 11-2 Probability and Punnett Squares. Genetics and Probability How do geneticists use the principles of probability? Probability – the likelihood that a particular event will occur

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11-2 Probability and Punnett Squares

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  1. Sexual Reproduction and Genetics Chapter 10 11-2 Probability and PunnettSquares • Genetics and Probability • How do geneticists use the principles of probability? • Probability – the likelihood that a particular event will occur • The principles of probability can be used to predict the outcomes of genetic crosses.

  2. Sexual Reproduction and Genetics Chapter 10 Punnett Squares • Punnett Squares– a tool used to determine the combinations from a genetic cross • Shows all possible combinations of gametes and likelihood each will occur

  3. Setting up a Punnett Square Draw the punnett square – size of your square depends on how many traits you are using (Ex. 1 trait = 4 boxes, 2 traits = 16 boxes) Gametes produced by each parent are shown along the top and left side. Possible gene combinations for the offspring appear in the four boxes. Sexual Reproduction and Genetics Chapter 10

  4. Gametes from the F1 generation parents are used to get the offspring for the F2 generation. Mendel only looked at one trait at a time in his first experiments Monohybrid cross– a cross involving one trait Sexual Reproduction and Genetics Chapter 10 Mendel’s Experiment

  5. Probablility and Segregation • One fourth (1/4) of the F2 plants have two alleles for tallness (TT). • 2/4 or 1/2 have one allele for tall (T), and one for short (t). • One fourth (1/4) of the F2 have two alleles for short (tt).

  6. Sexual Reproduction and Genetics Chapter 10 10.2 Mendelian Genetics Mendel’sLaw of Segregation • Two alleles for each trait separate during meiosis. • During fertilization, two alleles for that trait unite. • Heterozygous organisms are called hybrids.

  7. Sexual Reproduction and Genetics Chapter 10 10.2 Mendelian Genetics Monohybrid Cross • A cross that involves hybrids for a single trait is called a monohybrid cross.

  8. Sexual Reproduction and Genetics Chapter 10 10.2 Mendelian Genetics Dihybrid Cross • The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross. • Dihybrids are heterozygous for both traits.

  9. Sexual Reproduction and Genetics Chapter 10 10.2 Mendelian Genetics Law of Independent Assortment • Random distribution of alleles occurs during gamete formation • Genes on separate chromosomes sort independently during meiosis. • Each allele combination is equally likely to occur. • Law of independent assortment occurs during metaphase I of meiosis.

  10. Sexual Reproduction and Genetics Chapter 10 10.2 Mendelian Genetics Punnett Square—Dihybrid Cross • Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced. • The resulting phenotypic ratio is 9:3:3:1.

  11. Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism. Sexual Reproduction and Genetics • A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes. Chapter 10 10.3 Gene Linkage and Polyploidy Polyploidy

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