Questions and Answers
What is a gene?
An inherited factor encoded in the DNA that helps determine a characteristic.
What is an allele?
One of two or more alternative forms of a gene.
What does locus refer to?
Specific place on a chromosome occupied by an allele.
Define genotype.
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What is a heterozygote?
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What is a homozygote?
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What is a phenotype?
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Define characteristic in the context of genetics.
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The genotype is inherited.
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Organisms transmit their phenotypes to the next generation.
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Mendel's F2 plants showed a phenotypic ratio of approximately:
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A diploid organism is __________ at a locus if it possesses two identical alleles.
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What does the principle of segregation state?
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The concept of dominance means the recessive trait is always expressed in the phenotype.
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How did Mendel confirm his principles?
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What is the phenotypic ratio observed in a dihybrid cross?
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Study Notes
Basic Principles of Heredity
- Gene: An inherited factor encoded in DNA that influences characteristics.
- Allele: Variants of a gene that exist in different forms (e.g., dominant and recessive).
- Locus: Specific location on a chromosome where an allele is found.
- Genotype: The complete set of alleles possessed by an organism.
- Heterozygote: An organism with two different alleles at a given locus.
- Homozygote: An organism with identical alleles at a given locus.
- Phenotype: Observable traits or characteristics of an organism.
- Characteristic or Character: Features exhibited by an organism, such as color or size.
Genetic Interaction
- A genotype determines the potential for traits, but environmental factors also play a significant role in phenotypic expression.
- Some traits are primarily influenced by genetics, while others are more affected by environmental conditions.
- For example, the shape of Mendel's peas was mainly determined by genotype, whereas the height of an oak tree is significantly influenced by environmental factors.
Monohybrid Crosses
- Monohybrid Cross: A cross between individuals differing in one trait, often involving homozygous parents.
- In Mendel's experiments, he crossed pure-breeding peas with round and wrinkled seeds, leading to predictable offspring traits in the first (F1) and second (F2) generations.
- F1 generation exhibited only the dominant phenotype, while both traits appeared in the F2 generation in a 3:1 ratio of dominant to recessive traits.
Mendel's Conclusions
- Mendel hypothesized that organisms contain two alleles for each trait that segregate during gamete formation.
- The concept of dominance was established; dominant alleles mask the expression of recessive ones.
- The principle of segregation states that alleles separate with equal probability into gametes during reproduction.
Testcross and Phenotypic Ratios
- A testcross determines the genotype of an unknown individual by crossing it with a homozygous recessive organism.
- Phenotypic ratios from typical crosses include:
- 3:1 for heterozygous parents.
- 1:1 for a heterozygous and homozygous recessive cross.
- Uniform progeny in various homozygous crosses.
Dihybrid Crosses
- Dihybrid Cross: Crossing organisms differing in two traits, producing a 9:3:3:1 ratio among progeny.
- Mendel demonstrated the principle of independent assortment, indicating that alleles for different traits segregate independently during gamete formation.
Summary of Mendel's Laws
- Principle of Segregation: Each organism has two alleles for each trait, which segregate during gamete formation.
- Dominance Concept: In the presence of both alleles, only the dominant trait is expressed in the phenotype.
- Independent Assortment: The segregation of alleles for one trait does not influence the segregation of alleles for another trait.
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Description
This quiz explores the fundamental concepts of heredity, including key terms such as gene, allele, genotype, and phenotype. Learn about how genetic interactions shape the traits of organisms and the role of the environment in phenotypic expression. Test your understanding of these principles in genetics.