CHAPTER 14
MENDEL AND THE GENE IDEA

OBJECTIVES

  1. Explain how Mendel’s hypothesis of inheritance differed from the blending theory of inheritance.*
  2. List several features of Mendel’s methods that contributed to his success.*
  3. State, in your own words, Mendel’s law of segregation.*
  4. Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic and genotypic ratios of the F2 generation.*
  5. Distinguish between genotype and phenotype; heterozygous and homozygous; dominant and recessive.*
  6. Explain how a testcross can be used to determine if a dominant phenotype is homozygous or heterozygous.*
  7. State, in your own words, Mendel’s law of independent assortment.*
  8. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic ratios of the F2 generation.*
  9. Using the laws of probability, use the product (multiplication) rule to make predictions for a trihybrid or tetrahybrid cross between two individuals.*
  10. Explain how the phenotypic expression of the heterozygote is affected by complete dominance, incomplete dominance and codominance.*
  11. Describe the inheritance of the ABO blood system and explain why the IA and IB alleles are said to be codominant.
  12. Define and give examples of pleiotropy.*
  13. Describe a simple model for polygenic inheritance, and explain why most polygenic characters are described in quantitative terms.*
  14. Describe how environmental conditions can influence the phenotypic expression of a character.*
  15. Describe the inheritance and expression of sickle-cell disease.*
  16. Explain how a lethal gene can be maintained in a population.*
  17. Explain why lethal dominant genes are much more rare than lethal recessive genes.*
  18. Give an example of a late-acting lethal dominant in humans and explain how it can escape elimination.*
  19. Describe common practices for fetal screening and newborn screening for genetic diseases.*

KEY TERMS

Blending theory, Gregor Mendel, true-breeding, P generation, F1 generation, F2 generation, Mendel’s law of segregation, alleles, dominant allele, recessive allele, homozygous, heterozygous, phenotype, genotype, monohybrid, testcross, dihybrid, Mendel's law of independent assortment, incomplete dominance, codominance, multiple alleles, ABO blood system, pleiotropy, polygenic inheritance, lethal recessive, carriers, sickle-cell disease, lethal dominant, Huntington’s disease, multifactorial traitsPKU, CVS, amniocentesis, karyotyping.