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 genotype and phenotype combinations of 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., AA or aa).

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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., Aa).

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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., A in Aa).

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What is a recessive allele?

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

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What is the genotype of offspring from a cross between two heterozygous red flowers (Rr)?

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25% homozygous dominant (RR), 50% heterozygous (Rr), 25% homozygous recessive (rr).

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What is the phenotype of offspring from a cross between two heterozygous red flowers (Rr)?

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75% red flowers, 25% white flowers.

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What is the genotype of offspring from a cross between a green pea plant (Gg) and a yellow pea plant (gg)?

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50% heterozygous (Gg), 50% homozygous recessive (gg).

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What is the phenotype of offspring from a cross between a green pea plant (Gg) and a yellow pea plant (gg)?

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50% green peas, 50% yellow peas.

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What is the genotype of offspring from a cross between two white flowers (rr)?

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100% homozygous recessive (rr).