Bio 181, Fall 2005

Learning Objectives for Chapter 14, Mendel and the Gene Idea

Understand and be able to use the following terms:

character	trait	cross	wild-type
true-breeding	hybridization	P generation	F1 generation
F2 generation	alleles	dominant	recessive
law of segregation	Punnett square	homozygous	heterozygous
genotype	phenotype	testcross	monohybrid
dihybrid	law of independent assortment	rule of multiplication	rule of addition
incomplete dominance	complete dominance	codominance	multiple alleles
pleiotropic	epistasis	quantitative characters	polygenic inheritance
norm of reaction	pedigree	cystic fibrosis	Tay-Sachs disease
sickle cell disease	Huntington’s Disease	consanguinity	amniocentesis
chorionic villus sampling

1. Explain how observations by Mendel and others and Mendel's hypothesis of inheritance differed from the blending theory of inheritance.

2. List the features of Mendel's methods that contributed to his success. Why were garden peas a good experimental organism for Mendel's study of genetics? How did Mendel control fertilization of the pea plants? Why was this important for conducting genetic experiments?

3. What is a wild type trait?

4. Define true breeding, hybridization, monohybrid cross, P generation, F₁ generation, and F₂ generation.

5. List and explain the four components of Mendel's hypothesis that led him to deduce the law of segregation.

6. Explain how Mendel's law of segregation got its name.

7. Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic and genotypic ratios of the F₂ generation. If given the genotypes of offspring, be able to give the genotypes of parents.

8. Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype.

9. Explain how a testcross can be used to determine if a dominant phenotype is homozygous or heterozygous.

10. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic ratios of the F₂ generation. If given the genotypes of offspring, be able to give the genotypes of parents.

11. Define Mendel's law of independent assortment.

12. Distinguish between the law of Segregation and the law of Independent Assortment. Be able to explain them using your own words. Distinguish between a monohybrid cross and a dihybrid cross. Which demonstrates the law of segregation? Which demonstrates the law of independent assortment?

13. Use the rule of multiplication to calculate the probability that a particular F₂ individual will be homozygous recessive or dominant.

14. Given a Mendelian cross, use the rule of addition to calculate the probability that a particular F₂ individual will be heterozygous.

15. Explain why Mendel was wise to use large sample sizes in his studies.

16. Give an example of incomplete dominance and explain why it is not evidence for the blending theory of inheritance.

17. Explain how the phenotypic expression of the heterozygote is affected by complete dominance, incomplete dominance, and co-dominance.

18. Explain why Tay-Sachs is considered recessive at the organismic level but co-dominant at the molecular level.

19. Explain why genetic dominance does not mean that the dominant allele subdues a recessive allele. Illustrate your explanation with the use of the round versus wrinkled pea seed shape.

20. Describe the inheritance of the ABO blood system and explain why the I^A and I^B alleles are said to be co-dominant.

21. Define and give examples of pleiotropy and epistasis.

22. Explain why dominant alleles do not necessarily mean that the allele is more common in a population. Illustrate your explanation with the character polydactyly

23. Describe a simple model for polygenic inheritance and explain why most polygenic characters are described in quantitative terms.

24. Describe how environmental conditions can influence the phenotypic expression of a character. Explain what is meant by "a norm of reaction."

25. Explain why studies of human inheritance are not as easily conducted as Mendel's work with his peas.

26. Be able to read a family pedigree to figure out probable genotypes of family members (for example, whether a family member is likely to be a carrier). Recognize what the squares, circles, and colored symbols represent.

27. Explain how a lethal recessive gene can be maintained in a population.

28. Explain why consanguinity increases the probability of homozygosity in offspring.

29. Explain why lethal dominant genes are much rarer than lethal recessive genes. Give an example of a late-acting lethal dominant in humans and explain how it can escape elimination.

30. Define and give examples of multifactorial disorders in humans. Explain what can currently be done to reduce the frequency of these diseases.

31. Explain how carrier recognition, fetal testing, and newborn screening can be used in genetic screening and counseling.