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Published bySpencer Pearson Modified over 9 years ago
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Heredity, Genetics Punnett Squares & Probability Mr. Miller
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Lets find out if the two pigeons on the left produce offspring that have the traits of the pigeon on the right
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To do this we must understand how to use a Punnet Square What is a Punnet Square? A chart that allows us to determine the different genotypes that offspring can inherit from their parents
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Lets see how to use it First we must get the genotype of each parent Example: T: allele for tallness t: allele for shortness tt – mothers genotype Tt – fathers genotype
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Now lets set up the Punnet Square Tt t t T T t t tt tt
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What are the number of genotypes for the traits the offspring can inherit? Tttt Tttt Tt t t The offspring can inherit two sets of genes that will produce a tall phenotype The offspring can inherit two sets of genes that will produce a short phenotype
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Now lets talk about probability What is probability? Probability is the chance that an event will occur How do you find the probability of an event? You must know: the number of specific events the number of possible events
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Lets find the probability the child will be tall How many genotypes will produce a tall offspring? Tttt Tttt 2 What are number of possible genotypes? 4 Tt t t
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Now lets find the probability! Probability = Number of specific event 2 1 Number of possible events 4 2 The probability of having a tall offspring is ½, 1:2, or 50%
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Now try this one Determine the types of genes an offspring can inherit from parents that have the following genotypes: Zz - father’s genotype Zz - mother’s genotype Z: gene for gray feathers z: allele for white feathers Z Z z z z zz Z Z Z z Z
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Now lets look at the possible genotypes and the phenotypes that will be expressed Z Z z z z zz Z Z Z z Z There is a single possibility of inheriting a homozygous (pure) dominant genotype which will produce a phenotype with grey feathers There are two possibilities of inheriting heterozygous (hybrid) genotypes which will produce a phenotype with grey feathers
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Now lets look at the possible genotypes and the phenotypes that will be expressed Z Z z z z zz Z Z Z z Z There is a single possibility of inheriting a homozygous (pure) recessive genotype which will produce a phenotype with white feathers So two grey birds can produce a pigeon with white feathers!
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Now lets find the probability Lets find the probability the offspring will have grey feathers. = ZZZz zz Z Z z z
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Now lets find the probability Lets find the probability the offspring will have white feathers. = ZZZz zz Z Z z z
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