Multiple Choice
Which of the following is a way in which monosomy can occur?
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6. Chromosomal Variation
Chromosomal Mutations: Aneuploidy
1:32 minutesProblem 1a
Textbook Question
How was it established that particular phenotypes are inherited as a result of genetic information present in the chloroplast rather than in the nucleus?
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Understand the concept of extranuclear inheritance: Extranuclear inheritance refers to the transmission of genetic information through organelles like mitochondria and chloroplasts, rather than through nuclear DNA. This is often referred to as cytoplasmic inheritance.
Review experimental evidence: Scientists have used reciprocal crosses to determine whether a trait is inherited through the nucleus or the cytoplasm. In reciprocal crosses, the phenotypes of the offspring are compared when the trait is inherited from the mother versus the father.
Analyze maternal inheritance patterns: If a trait is consistently inherited from the mother regardless of the father's phenotype, it suggests that the genetic information responsible for the trait is located in the cytoplasm (e.g., in the chloroplasts or mitochondria), as these organelles are typically inherited maternally.
Consider experiments involving organelle DNA: Researchers have isolated and sequenced DNA from chloroplasts to identify genes responsible for specific traits. By comparing these genes to nuclear DNA, they confirmed that certain phenotypes are linked to chloroplast DNA.
Examine mutant studies: Mutant strains with defects in chloroplast function have been used to demonstrate that specific phenotypes (e.g., variegated leaf patterns) are associated with chloroplast DNA mutations, further supporting the role of chloroplasts in extranuclear inheritance.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Extranuclear Inheritance
Extranuclear inheritance refers to the transmission of genetic material that occurs outside the nucleus, primarily through organelles like mitochondria and chloroplasts. This type of inheritance is distinct from Mendelian inheritance, which involves nuclear DNA. In plants, traits such as leaf color can be influenced by the genetic information in chloroplasts, which is inherited maternally, meaning offspring receive their chloroplast DNA exclusively from the mother.
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Maternal Effect
The maternal effect is a phenomenon where the genotype of the mother directly influences the phenotype of her offspring, regardless of the offspring's own genotype. This occurs because the mother provides cytoplasmic factors, such as RNA and proteins, during oogenesis. In the context of chloroplast inheritance, the maternal genotype can determine traits in the offspring, as the chloroplasts are inherited from the mother, affecting characteristics like pigmentation or growth patterns.
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Experimental Evidence for Chloroplast Inheritance
Establishing that certain phenotypes are inherited through chloroplasts rather than nuclear DNA often involves experimental crosses and phenotypic analysis. Researchers may perform reciprocal crosses, where they switch the maternal and paternal contributions, to observe differences in offspring traits. If the phenotype is consistent with the maternal genotype regardless of the paternal contribution, it supports the conclusion that the trait is linked to chloroplast inheritance.
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