Genetics: Punnett Square

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What is a Punnett Square?

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A Punnett Square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross.

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What does homozygous mean?

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Homozygous refers to having two identical alleles for a particular gene (e.g., BB or bb).

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What does heterozygous mean?

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Heterozygous refers to having two different alleles for a particular gene (e.g., Bb).

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What is a dominant allele?

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A dominant allele is an allele that expresses its trait even when only one copy is present (e.g., B in Bb).

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What is a recessive allele?

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A recessive allele is an allele that only expresses its trait when two copies are present (e.g., bb).

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What is the phenotype of an organism?

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The phenotype is the observable physical or biochemical characteristics of an organism, determined by its genotype.

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What is the genotype of an organism?

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The genotype is the genetic makeup of an organism, represented by the alleles it possesses (e.g., BB, Bb, or bb).

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If a homozygous dominant brown mouse (BB) is crossed with a heterozygous brown mouse (Bb), what are the possible genotypes of the offspring?

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50% BB (homozygous dominant) and 50% Bb (heterozygous).

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In a cross between two heterozygous rabbits (Bb), what is the expected phenotype ratio of the offspring?

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75% white (dominant) and 25% brown (recessive).

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What is the expected phenotype of offspring from a tall plant (Tt) crossed with a short plant (tt)?

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50% tall and 50% short.