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 of a particular cross or breeding experiment. It shows the possible combinations of alleles from the parents.

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What does homozygous mean?

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Homozygous refers to having two identical alleles for a particular gene, such as TT or rr.

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What does heterozygous mean?

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Heterozygous refers to having two different alleles for a particular gene, such as Tt.

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What is a genotype?

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A genotype is the genetic makeup of an organism, represented by the alleles it possesses, such as TT, Tt, or tt.

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What is a phenotype?

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

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What is the difference between dominant and recessive alleles?

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Dominant alleles are expressed in the phenotype even if only one copy is present (e.g., T), while recessive alleles are only expressed if two copies are present (e.g., tt).

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If a tall plant (TT) is crossed with a tall plant (Tt), what are the possible genotypes of the offspring?

Back

50% homozygous dominant (TT) and 50% heterozygous (Tt).

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What is the expected phenotype of the offspring from a TT x Tt cross?

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100% tall plants.

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What is the expected genotype of the offspring from a white flower (rr) crossed with another white flower (rr)?

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100% homozygous recessive (rr).

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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?

Back

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