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

3. Extensions to Mendelian Inheritance

Overview of interacting Genes

Genetics

3. Extensions to Mendelian Inheritance

Overview of interacting Genes

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2:10 minutes

Problem 7d

Textbook Question

Provide a definition and an example for each of the following terms:
Polygenic inheritance

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Polygenic inheritance refers to a type of genetic inheritance where a single trait is controlled by two or more genes, often located on different chromosomes. These genes contribute to the phenotype in an additive or interactive manner, resulting in a continuous range of phenotypes rather than discrete categories.

An example of polygenic inheritance is human skin color. Skin color is determined by the interaction of multiple genes, each contributing to the amount of melanin produced. The combined effect of these genes results in a wide spectrum of skin tones.

To understand polygenic inheritance, consider that each gene involved may have two or more alleles, and the cumulative effect of these alleles determines the phenotype. For instance, alleles that promote higher melanin production will add to the overall pigmentation.

Polygenic traits often exhibit a bell-shaped distribution in a population, as seen in traits like height, where most individuals fall near the average, with fewer individuals at the extremes.

In summary, polygenic inheritance involves multiple genes contributing to a single trait, leading to continuous variation. This is distinct from Mendelian inheritance, where traits are typically determined by a single gene with clear dominant and recessive alleles.

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Key Concepts

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

Polygenic Inheritance

Polygenic inheritance refers to the genetic mechanism where multiple genes (often located on different chromosomes) contribute to a single trait. This results in a continuous range of phenotypes, rather than discrete categories. For example, human height is influenced by several genes, leading to a wide variety of heights in the population.

Quantitative Traits

Quantitative traits are characteristics that are influenced by multiple genes and can be measured on a continuous scale. These traits often show a normal distribution in a population due to the additive effects of alleles. Examples include traits like weight, skin color, and intelligence, which are not simply 'present' or 'absent' but vary in degree.

Environmental Influence

Environmental influence refers to the impact of external factors on the expression of genetic traits. In polygenic inheritance, the phenotype can be significantly affected by environmental conditions such as nutrition, climate, and lifestyle. For instance, two individuals with the same genetic predisposition for height may end up differing in height due to variations in their nutrition during growth.

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Textbook Question

Describe the difference between continuous phenotypic variation and discontinuous variation. Explain how polygenic inheritance could be the basis of a trait showing continuous phenotypic variation. Explain how polygenic inheritance can be the basis of a threshold trait.

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