Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

20. Quantitative Genetics

Traits and Variance

Genetics

20. Quantitative Genetics

Traits and Variance

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1:46 minutes

Problem 2

Textbook Question

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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Step 1: Define Mendelian Inheritance - Mendelian inheritance refers to the patterns of inheritance that are characteristic of organisms that reproduce sexually. These patterns were first described by Gregor Mendel in the 19th century. Mendelian inheritance involves discrete traits that are determined by a single gene with two alleles, where one allele is dominant and the other is recessive. Examples include pea plant traits such as flower color and seed shape.

Step 2: Explain Neo-Mendelian Inheritance - Neo-Mendelian inheritance expands on Mendel's original principles by incorporating more complex genetic phenomena such as incomplete dominance, codominance, multiple alleles, and epistasis. These modes of inheritance still involve discrete traits but recognize that the interactions between alleles can be more complex than simple dominance and recessiveness.

Step 3: Describe Quantitative Inheritance - Quantitative inheritance, also known as polygenic inheritance, involves traits that are controlled by multiple genes, each contributing a small effect to the phenotype. These traits do not follow the simple Mendelian ratios and are often influenced by environmental factors. Examples include human height, skin color, and weight.

Step 4: Compare Qualitative and Quantitative Inheritance - Qualitative inheritance (Mendelian and neo-Mendelian) involves traits that are typically categorical and can be easily classified, such as flower color or blood type. In contrast, quantitative inheritance involves traits that are continuous and measured on a scale, such as height or intelligence, resulting from the cumulative effect of many genes.

Step 5: Discuss the Implications of Each Type of Inheritance - Understanding the difference between qualitative and quantitative inheritance is crucial for fields such as agriculture, medicine, and evolutionary biology. Qualitative traits are often easier to manipulate through selective breeding, while quantitative traits require more sophisticated statistical methods to analyze and predict due to their complex genetic and environmental interactions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which describe how traits are passed from parents to offspring through discrete units called genes. This mode of inheritance is characterized by clear-cut, qualitative traits that follow predictable patterns, such as dominant and recessive alleles. Mendelian inheritance is foundational for understanding basic genetic principles and is often illustrated through Punnett squares.

Neo-Mendelian Inheritance

Neo-Mendelian inheritance expands on Mendel's original concepts by incorporating findings from molecular biology and population genetics. It recognizes that inheritance can be influenced by multiple genes (polygenic inheritance) and environmental factors, leading to more complex patterns of trait expression. This approach allows for a better understanding of traits that do not fit neatly into Mendelian categories, such as those influenced by multiple alleles or gene interactions.

Quantitative Inheritance

Quantitative inheritance refers to the genetic basis of traits that exhibit continuous variation, such as height or weight, rather than discrete categories. These traits are typically controlled by multiple genes (polygenic traits) and are influenced by environmental factors, resulting in a bell-shaped distribution in a population. Understanding quantitative inheritance is crucial for fields like agriculture and medicine, where traits are often measured on a scale rather than classified as present or absent.

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Textbook Question

Which of the following traits would you expect to be inherited as quantitative traits?

Fruit weight in tomatoes

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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 threshold traits are actually polygenic even though they may have as few as two discrete phenotypic classes?

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Textbook Question

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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Textbook Question

A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red F₁. When the F₁ plants are interbred, an F₂ generation is produced in a ratio of 1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white. Further crosses reveal that the dark-red and white F₂ plants are true breeding

How many additive alleles are needed to produce each possible phenotype?

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Textbook Question

Based on the ratios in the F₂ population, how many genes are involved in the production of color?

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Textbook Question

The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of many eukaryotes are complex in organization and contain 5' and 3' flanking regions as well as introns. Researchers have compared the nucleotide sequence of two cloned alleles of the γ-globin gene from a single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and three short DNA segments that have been inserted in one allele or deleted in the other. None of the changes takes place in the gene's exons (coding regions). Why do you think this is so, and should it change our concept of genetic variation?

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Textbook Question

List as many human traits as you can that are likely to be under the control of a polygenic mode of inheritance.

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