Genes and Alleles

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What is a gene?

Back

A gene is a segment of DNA that contains the instructions for building a specific protein or set of proteins, which determine traits in an organism.

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What is an allele?

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An allele is a variant form of a gene that can produce different traits. For example, the gene for flower color in pea plants has alleles for purple and white.

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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 PP or pp.

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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 Pp.

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What is the difference between genotype and phenotype?

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Genotype is the genetic makeup of an organism (the alleles it carries), while phenotype is the observable expression of that genetic makeup (the traits displayed).

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What is a dominant allele?

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A dominant allele is one that expresses its trait even when only one copy is present in the genotype (e.g., P in Pp).

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What is a recessive allele?

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A recessive allele is one that only expresses its trait when two copies are present in the genotype (e.g., pp).

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What is a Punnett square?

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A Punnett square is a diagram used to predict the outcome of a genetic cross by showing the possible combinations of alleles from the parents.

Front

What is the phenotype of a Pp pea plant?

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The phenotype of a Pp pea plant is purple flowers, as purple (P) is dominant over white (p).

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What is the phenotype of a bb mouse?

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The phenotype of a bb mouse is brown fur, as brown (b) is recessive.