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Understanding Genetic Interactions: From Dominance to Environmental Influences

This chapter explores key concepts in genetics, including dominance among alleles, penetrance, expressivity, and the impact of lethal alleles on phenotypic ratios. It examines how multiple alleles can lead to diverse genotypes and phenotypes, and how gene interaction can shape single traits through epistasis. The chapter also highlights the influence of sex on inheritance, the phenomenon of anticipation in trait expression across generations, and the role of environmental factors on genotype expression. These themes deepen the understanding of genetic complexity.

lillian-underwood
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Understanding Genetic Interactions: From Dominance to Environmental Influences

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  1. Chapter 5 Outline • 5.1 Dominance Is Interaction between Genes at the Same Locus, 100 • 5.2 Penetrance and Expressivity Describe How Genes Are Expressed as Phenotype, 102 • 5.3 Lethal Alleles May Alter Phenotypic Ratios, 103 • 5.4 Multiple Alleles at a Locus Create a Greater Variety of Genotypes and Phenotypes than Do Two Alleles, 103

  2. Chapter 5 Outline • 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype, 105 • 5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways, 114 • 5.7 Anticipation Is the Stronger or Earlier Expression of Traits in Succeeding Generations, 122 • 5.8 The Expression of a Genotype May Be Influenced by Environmental Effects, 122

  3. 5.1 Dominance Is Interaction between Genes at the Same Locus • Genes at the same locus – two versions of the same gene; each version of the same gene is defined as allele.

  4. 5.1 Dominance Is Interaction between Genes at the Same Locus • Incomplete dominance • Codominance

  5. 5.2 Penetrance and Expressivity Describe How Genes Are Expressed as Phenotype • Penetrance: percentage of individuals having a particular genotype that express the expected phenotype • Expressivity: the degree to which a character is expressed

  6. 5.3 Lethal Alleles May Alter Phenotypic Ratios • A lethal allele: causes death at an early stage of development, and so some genotypes may not appear among the progeny

  7. More than 2 alleles at a locus Relationship between allele pairs determines outcome Could be exhibited as dominant/recessive relationship as in duck feathers Could be exhibited in codominance as in ABO blood type

  8. 5.4 Multiple Alleles at a Locus Create a Greater Variety of Genotypes and Phenotypes than Do Two Alleles • ABO blood group

  9. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype • Gene interaction: Effects of genes at one locus depend on the presence of genes at other loci. • Gene interaction that produces novel phenotypes

  10. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype • Gene interaction with epistasis • Epistasis: One gene masks the effect of another gene. • Recessive epistasis

  11. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype • Dominant epistasis

  12. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype • Duplicate recessive epistasis

  13. 5.5 Gene Interaction Occurs When Genes at Multiple Loci Determine a Single Phenotype • Complementation: determines whether mutations are at the same locus or at different loci • The complex genetics of coat color in dogs: • Agouti (A) locus • Black (B) locus • Extension (E) locus • Spotting (S) locus

  14. 5.6 Sex Influences the Inheritance and Expression of Genes in a Variety of Ways • Sex-influenced and sex-limited characteristics

  15. Sex-influenced and sex-limited characteristics • Sex-influenced characteristics

  16. Sex-influenced and sex-limited characteristics • Sex-limited characteristics

  17. Sex-influenced and sex-limited characteristics • Cytoplasmic inheritance

  18. Sex-influenced and sex-limited characteristics • Genetic maternal effect

  19. Sex-influenced and sex-limited characteristics • Genomic imprinting: differential expression of genetic material depending on whether it is inherited from the male or female parent • Epigenetics: phenomena due to alterations to DNA that do not include changes in the base sequence; often affects the way in which the DNA sequences are expressed

  20. 5.7 Anticipation Is the Stronger or Earlier Expression of Traits in Succeeding Generations • Anticipation: A genetic trait becomes more strongly expressed or is expressed at an earlier stage as it is passed from generation to generation.

  21. 5.8 The Expression of a Genotype May Be Influenced by Environmental Effects • Temperature-sensitive allele: an allele whose product is functional only at a certain temperature

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