Name______________________________ Class __________________ Date _______
Reading Guide

 to Genetics

Section 11–1 The Work of Gregor Mendel (pages 308-312)


The Experiments of Gregor Mendel

Match the term with its definition.

Term                             Definition

             1.    genes         A. Specific characteristics that vary among individuals

             2.    hybrids      B. The offspring of true-breeding parents with different traits

             3.    traits          C. Factors that determine traits

             4.    alleles        D. Sex cells, egg or sperm

             5.    gametes     E. The different forms of a gene


6. Why are peas a good model system for studying heredity?


7. What does it mean when pea plants are described as being true-breeding?


8. How did Mendel cross-pollinate flowers?


9. What is the difference between a gene and an allele?


10. State the principle of dominance.



The table shows some crosses between true-breeding parents that carry pairs of dominant alleles (such as SS) or pairs of recessive alleles (such as ss). Complete the table to show the combination of alleles in the offspring. Then use it to answer Questions 11-12.




11. What is the dominant shape of a pea pod? How do you know?



12. What symbol represents the recessive allele for pod color?




13. What is segregation? What is the result of segregation?



14. The capital letter G represents the allele in peas that causes the dominant trait, gray seed coat. The lower-case letter g represents the recessive allele that causes the recessive trait, white seed coat. Complete the diagram to show how alleles segregate during the formation of gametes.


Section 11–2Applying Mendel’s Principles (pages 313–318)


Probability and Punnett Squares

15. What is probability?



16. In a parent pea plant with the allele pair Gg, what is the probability that one gamete will contain the G allele?



17. Complete the graphic organizer to define the characteristics of homozygous and heterozygous genotypes and phenotypes.












18. The dominant allele for smooth pod shape in peas is S. The recessive allele for constricted pod shape is s. In the Punnett square, show the result of crossing two heterozygous parents (Ss). Write the genotype and the phenotype of each type of offspring in the space provided.
















For Questions 19-23, refer to the Punnett square above.

19. What is the probability of a heterozygous offspring? Explain your answer.



20. What is the probability of a homozygous offspring? Explain.



21. What is the probability of a homozygous recessive offspring?



22. What is the probability of a smooth phenotype?



23. What is the probability of a homozygous recessive individual (ss) producing a gamete with a dominant allele (S)? Explain.



Independent Assortment

24. State the principle of independent assortment below.



25. Using the principle of independent assortment, what are the four possible gametes produces from a heterozygous round, heterozygous yellow pea (RrYy)?



Summary of Mendel’s Principles

26. The units that determine the inheritance of biological characteristics are                          .

27. A form of a gene is a(n)                          .

28. If two or more forms of a gene exist, some may be dominant and others may be _______.

29. The offspring of most sexually reproducing organisms have two copies of each gene. One came from each .

30. Alleles from different genes usually                        independently from each other when gametes form.


Section 11–4 Meiosis (pages 323-329)


Chromosome Number

For Questions 31–38, write True if the statement is true. If the statement is false, change the underlined word to make the statement true.

                                   31.  The offspring of two parents obtains a single copy of every gene from each parent.

                                   32.  A gamete must contain one complete set of genes.

                                   33.  Genes are located at specific positions on spindles.

                                   34.  A pair of corresponding chromosomes is homozygous.

                                   35.  One member of each homologous chromosome pair comes from each gene.

                                   36.  A cell that contains both sets of homologous chromosomes is haploid.

                                   37.  The gametes of sexually reproducing organisms are haploid.

                                   38.  If an organism’s haploid number is 6, its diploid number is 3.


Phases of Meiosis

On the lines provided, identify the stage of meiosis I or meiosis II in which the event described occurs.

                                 39.  Each replicated chromosome pairs with its corresponding homologous chromosome.

                           40.  Crossing-over occurs between tetrads.

                       41.  Paired homologous chromosomes line up across the center of the cell.

                      42.  Spindle fibers pull each homologous chromosome pair toward an opposite end of the cell.

                       43.  A nuclear membrane forms around each cluster of chromosomes and cytokinesis follows, forming two new cells.

                       44.  Chromosomes consist of two chromatids, but they do not pair to form tetrads.

                       45.  A nuclear membrane forms around each cluster of chromosomes and cytokinesis follows, forming four new cells.


46. What does the diagram show?




47. During what phase of meiosis does this process occur?



48. What is the result of this process?




Comparing Meiosis and Mitosis

49. Complete the table to compare meiosis and mitosis.





Form of reproduction



Number of daughter cells



Change in chromosome number



Number of cell divisions



Difference in alleles between parent cell and daughter cells




50. A diploid cell that enters mitosis with 16 chromosomes will divide to produce                  daughter cells.

Each of these daughter cells will have                                                                                      chromosomes.

51. If the diploid number of chromosomes for an organism is 16, each daughter cell after mitosis will contain  chromosomes.

52. A diploid cell that enters meiosis with 16 chromosomes will pass through                         cell divisions,

producing                                                            daughter cells, each with                               chromosomes.

53. Gametes have a                            number of chromosomes.

54. If an organism’s haploid number is 5, its diploid number is                           .

55. While a haploid number of chromosomes may be even or odd, a diploid number is always         .


Gene Linkage and Gene Maps

56. What did Thomas Hunt Morgan discover that seemed to violate Mendel’s principles?



57. How did Morgan explain his finding?



58. Look at Figure, 11-18, which pairs of characteristics are more likely to cross over: curved wing and dumpy wing; or curved wing and vestigial (small) wing? Why?



59. Which pair of genes shown is least likely to cross over? How do you know?