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Ch. 20 - Quantitative Genetics and Multifactorial Traits
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Non è quello che usi tu?Cambia libro di testo
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Capitolo 20, Problema 1b

What findings led geneticists to postulate the multiple-factor hypothesis that invoked the idea of additive alleles to explain inheritance patterns?

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Understand the historical context: Early geneticists observed that some traits did not follow simple Mendelian inheritance patterns, such as traits showing continuous variation (e.g., height, skin color) rather than discrete categories.
Recognize the key observation: These continuously varying traits suggested that multiple genes, rather than a single gene, influenced the phenotype, leading to the idea that many factors contribute to the trait.
Examine the experimental evidence: Geneticists noticed that when multiple genes affect a trait, their effects can add up in an additive manner, producing a range of phenotypes rather than just a few distinct classes.
Connect the concept of additive alleles: The multiple-factor hypothesis proposed that each gene involved contributes a small, additive effect to the overall phenotype, explaining the continuous distribution of traits.
Summarize the conclusion: The combination of continuous variation, the involvement of multiple genes, and the additive effects of alleles led to the formulation of the multiple-factor hypothesis to explain complex inheritance patterns.

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Multiple-Factor Hypothesis

The multiple-factor hypothesis proposes that traits are influenced by several genes, each contributing a small additive effect. This contrasts with single-gene inheritance and helps explain continuous variation in traits like height or skin color.
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06:14
Multiple Cross Overs and Interference

Additive Alleles

Additive alleles are gene variants whose effects sum up to influence a trait quantitatively. Each allele adds a certain amount to the phenotype, leading to a range of possible trait values rather than discrete categories.
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03:03
New Alleles and Migration

Continuous Variation and Quantitative Traits

Continuous variation refers to traits that show a range of phenotypes rather than distinct classes, often influenced by multiple genes and environmental factors. Observations of such traits led geneticists to seek explanations beyond Mendelian single-gene models.
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Percorso guidato
13:40
Traits and Variance
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Write a short essay that discusses the difference between the more traditional Mendelian and neo-Mendelian modes of inheritance (qualitative inheritance) and quantitative inheritance.

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How can we ascertain the number of polygenes involved in the inheritance of a quantitative trait?

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How do we know that monozygotic twins are not identical genotypically as adults?

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How do we assess environmental factors to determine if they impact the phenotype of a quantitatively inherited trait?

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