Chapter Objectives

1. Describe the favored model of heredity in the 19th century prior to Mendel and explain how this model was inconsistent with observations
2. Explain how Mendel's hypothesis of inheritance differed from the blending theory of inheritance
3. list several features of Mendel's methods that contributed to his success
4. List 4 components of Mendel's hypothesis that led him to deduce the Law of Segregation
5. State the Law of Segregation
6. Use a Punnett square to predict the results of a monohybrid cross and state the phenotypic and genotypic ratios of the F₂ generation
7. Distinguish between genotype and phenotype, heterozygous and homozygous, and dominant and recessive
8. Explain how a testcross can be used to determine if a dominant phenotype is homozygous or heterozygous
9. Define random event and explain why it is significant that allele segregation during meiosis and fusion of gametes at fertilization are random events
10. Use the rule of multiplication to calculate the probability that a particular F₂ individual will be homozygous recessive or dominant
11. Given a Mendelian cross, use the rule of addition to calculate the probability that a particular F₂ individual will be heterozygous
12. Describe 2 alternate hypotheses that Mendel considered for how 2 characters might segregate during gamete formation and explain how he tested these hypotheses
13. State the Law of Independent Assortment
14. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic and genotypic rations of the F₂ generation.
15. Using the laws of probability, predict from a trihybrid cross between 2 individuals that are heterozygous for all 3 traits what expected proportion of the offspring would be
    1. Homozygous for all 3 traits
    2. Heterozygous for all 3 traits
    3. Homozygous recessive for 2 specific traits and heterozygous for the 3rd
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 codominance
18. Describe the inheritance of the ABO blood system and explain why the I^A and I^B alleles are said to be codominant
19. Define and give examples of pleiotropy
20. Explain what is meant by the phrase :one gene is epistatic to another
21. Explain how epistasis affects the phenotypic ration for a dihybrid cross
22. Describe a simple model for polygenic inheritance and explain why most polygenic characters are described in quantitative terms
23. Describe how environmental conditions can influence the phenotypic expression of a character
24. Given a simple family pedigree, deduce the genotypes for some of the family members
25. Describe the inheritance and expression of cystic fibrosis, Tay-Sachs disease, and sickle-cell disease
26. Explain how a lethal recessive gene can be maintained in a population
27. Explain why consanguinity increases the probability of homozygosity in offspring
28. Give an example of a late-acting lethal dominant in humans and explain how it can escape elimination
29. Explain how carrier recognition, fetal testing, and newborn screening can be used in genetic screening and counseling

****************

30. Explain how the observations of cytologists and geneticists provided the basis for the chromosome theory of inheritance
31. Describe the contributions that Thomas Hunt Morgan, Walter Sutton, and A. H. Sturtevant made to the current understanding of chromosomal inheritance
32. Explain why Drosophila melanogaster is a good experimental organism
33. Define linkage and explain why linkage interferes with independent assortment
34. Distinguish between parental and recombinant phenotypes
35. Explain how crossing over can unlink genes
36. Map a linear sequence of genes on a chromosome using given recombination frequencies from experimental crosses
37. Explain what additional information cytological maps provide over crossover maps
38. Distinguish between heterogametic sex and homogametic sex
39. Describe sex determination in humans
40. Describe the inheritance of a sex-linked gene such as color blindness
41. Explain why a recessive sex-linked gene is always expressed in human males
42. Explain how an organism compensates for the fact that some individuals have a double dosage of sex-linked genes while others have only one
43. Distinguish among nondisjunction, aneuploiody, and polypolidy; explain how these major chromosomal changes occur; and describe the consequences of their occurrence
44. Distinguish between trisomy and triploidy
45. Distinguish among deletions, duplications, translocations, and inversions
46. Describe the effects of alterations in chromosome structure and explain the role of position effects in altering phenotypes
47. Describe the type of chromosomal alterations implicated in the following human disorders: Down syndrome, Klinefelter syndrome, extra Y, triple-X syndrome, Turner syndrome, cri-du-chat syndrome, and chronic myelogenous leukemia
48. Define genome imprinting and provide evidence to support this model
49. Explain ho the complex expression of a human genetic disorder, such as fragile-X syndrome, can be influenced by triplet repeats and genomic imprinting
50. Give some exceptions to the chromosome theory of inheritance and explain why cytoplasmic genes are not inherited in a Mendelian fashion

Chapter Terms:

Chapter Outline Framework

1. Gregor Mendel's Discoveries
   1. Mendel brought an experimental and quantitative approach to genetics
   2. By the law of segregation, 2 alleles for a character are packaged into separate gametes
   3. By the law of independent assortment, each pair of alleles segregates into gametes independently
   4. Mendelian inheritance reflects probability rules
   5. Mendel discovered the particulate behavior of genes
2. Extending Mendelian Genetics
   1. The relationship between and genotype and phenotype is rarely simple
3. Mendelian Inheritance in Humans
   1. Pedigree analysis reveals Mendelian patterns in human inheritance
   2. Many human disorders follow Mendelian patterns of inheritance
   3. Technology provides new tools for genetic testing and counseling
4. Relating Mendelism to Chromosomes
   1. Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles
   2. Morgan traced a gene to a specific chromosome
   3. Linked genes tend to be inherited together because they are located on the same chromosome
   4. Independent assortment of chromosomes and crossing over produce genetic recombinants
   5. Geneticists can use recombination data to map a chromosome's genetic loci
5. Sex Chromosomes
   1. The chromosomal basis of sex varies with the organism
   2. Sex-linked genes have unique patterns of inheritance
6. Errors and Exceptions to Chromosomal Inheritance
   1. Alterations of chromosome number or structure cause some genetic disorders
   2. The phenotypic effects of some genes depend on whether they were inherited from the mother or father
   3. Extranuclear genes exhibit a non-Mendelian pattern of inheritance

back to top