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

2. Mendel's Laws of Inheritance

Mendel's Experiments and Laws

Genetics

2. Mendel's Laws of Inheritance

Mendel's Experiments and Laws

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1:28 minutes

Problem 2

Textbook Question

Write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.

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Begin by briefly stating Mendel's four postulates: (1) Unit factors in pairs, (2) Dominance and recessiveness, (3) Segregation, and (4) Independent assortment.

Explain the first postulate by correlating 'unit factors in pairs' with the modern concept that genes exist in pairs on homologous chromosomes, where each chromosome carries one allele of a gene.

For the second postulate, discuss dominance and recessiveness in terms of alleles, where one allele can mask the expression of another in a heterozygous genotype.

Relate the third postulate, segregation, to the behavior of homologous chromosomes during meiosis I, where alleles separate so that each gamete receives only one allele of each gene.

Finally, connect the fourth postulate, independent assortment, to the random orientation of different chromosome pairs during meiosis, which leads to the independent inheritance of genes located on different chromosomes.

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Key Concepts

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

Mendel's Four Postulates

Mendel's four postulates describe the basic principles of inheritance: unit factors (genes) exist in pairs, one from each parent; dominance and recessiveness determine trait expression; segregation of alleles occurs during gamete formation; and independent assortment of genes happens during gamete formation. These principles laid the foundation for classical genetics.

Genes and Alleles

Genes are segments of DNA that code for specific traits, and alleles are different versions of a gene found at the same locus on homologous chromosomes. Alleles can be dominant or recessive, influencing the phenotype depending on their combination, which explains Mendel's observations of trait inheritance.

Homologous Chromosomes and Segregation

Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that carry the same genes but may have different alleles. During meiosis, these chromosomes segregate independently into gametes, reflecting Mendel's law of segregation and independent assortment, which explains genetic variation.

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