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

Variations of Dominance

Genetics

3. Extensions to Mendelian Inheritance

Variations of Dominance

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1:13 minutes

Problem 1a

Textbook Question

How were early geneticists able to ascertain inheritance patterns that did not fit typical Mendelian ratios?

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Early geneticists observed inheritance patterns that deviated from Mendelian ratios by conducting controlled breeding experiments and analyzing the resulting phenotypic ratios in offspring. They noticed that some traits did not follow the expected 3:1 or 9:3:3:1 ratios predicted by Mendel's laws.

They hypothesized that factors such as incomplete dominance, codominance, multiple alleles, and gene interactions (epistasis) could influence inheritance patterns. For example, in incomplete dominance, heterozygotes exhibit an intermediate phenotype rather than a dominant one.

Geneticists also considered the possibility of linkage, where genes located close together on the same chromosome are inherited together, disrupting the independent assortment principle. They used test crosses and recombination frequency data to map gene locations.

They studied sex-linked traits, where genes located on sex chromosomes (e.g., X-linked traits) showed inheritance patterns that differed between males and females. This was particularly evident in traits like color blindness and hemophilia in humans.

Finally, they incorporated environmental influences and pleiotropy (one gene affecting multiple traits) into their analyses, recognizing that not all phenotypic variations could be explained solely by Mendelian genetics. These observations led to the development of more comprehensive models of inheritance.

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Key Concepts

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

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. His experiments with pea plants led to the formulation of key concepts such as dominant and recessive alleles, as well as the laws of segregation and independent assortment. These principles provide a foundational understanding of inheritance patterns, which serve as a baseline for identifying deviations in genetic ratios.

Non-Mendelian Inheritance

Non-Mendelian inheritance refers to patterns of inheritance that do not follow Mendel's laws. This includes phenomena such as incomplete dominance, codominance, and polygenic inheritance, where multiple genes influence a trait. Understanding these patterns is crucial for early geneticists as they observed traits that did not conform to expected Mendelian ratios, prompting further investigation into the complexities of genetic inheritance.

Quantitative Genetics

Quantitative genetics is the study of traits that are influenced by multiple genes and environmental factors, leading to continuous variation in phenotypes. Early geneticists utilized statistical methods to analyze these traits, which often resulted in bell-shaped distributions rather than discrete categories. This approach allowed them to identify inheritance patterns that deviated from Mendelian expectations, thereby expanding the understanding of genetic complexity.

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A situation where a single individual expresses two different alleles is referred to as:

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Which of the following is NOT a type of dominance?

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Which of the following parents could produce offspring with an AB blood type?

Blood types are an example of what type of dominance?

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Textbook Question

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). What ratio is obtained when platinum foxes are interbred? Is the P allele behaving dominantly or recessively in causing (a) lethality; (b) platinum coat color?

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Textbook Question

In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the F1 generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.

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Textbook Question

The ABO and MN blood groups are shown for four sets of parents (1 to 4) and four children (a to d). Recall that the ABO blood group has three alleles: I^A, I^B and i. The MN blood group has two codominant alleles, M and N. Using your knowledge of these genetic systems, match each child with every set of parents who might have conceived the child, and exclude any parental set that could not have conceived the child.

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