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Chapter 13
Patterns of Inheritance
CHAPTER OUTLINE
Inheritance in the garden pea
Mendel’s principles of inheritance
Genes occur in pairs and are inherited as parts of chromosomes
A dominant allele masks the expression of a recessive allele
A monohybrid cross involves a single pair of alleles at a given locus
Focus On: Solving Genetics Problems
Plants and People: Protecting Genetic Diversity in Crop Plants
CHAPTER OBJECTIVES
1. Define the following terms relating to genetic inheritance: dominant and recessive;
homozygous and heterozygous; genotype and phenotype.
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LECTURE OUTLINE
I. What is genetics? What is inheritance?
A. Who was Gregor Mendel?
B. How does sexual reproduction occur in the garden pea, a flowering plant? (a review)
C. What is self-fertilization vs. cross-fertilization?
III. If genes are parts of chromosomes and genes occur in pairs, how does this affect inheritance?
A. What is the difference between phenotype and genotype?
B. What are alleles? What is a gene locus?
C. What is a dominant trait? What is a recessive trait? How are these traits designated?
D. What is a monohybrid cross?
1. What is a Punnett square?
2. How do you use a Punnett square to predict the outcome of a monohybrid
cross?
E. What do homozygous and heterozygous mean?
B. What is the chromosomal theory of inheritance?
VI. What is linkage?
A. Why does linkage occur?
B. What is crossing over?
1. When does it occur?
2. How does it produce new combinations of genes?
C. How can linkage be used to produce genetic maps? Why is this useful?
VII. How do you explain the inheritance of some characters that don’t follow the rules of simple
Mendelian rules?
KEY TERMS
allele, p. 259
chromosome theory of
inheritance, p. 265
heterozygous, p. 260
homozygous, p. 260
incomplete dominance,
principle of dominance,
p. 258
principle of independent
TEACHING TIPS
1. Students are usually interested in traditional Mendelian genetics. Emphasize the ground-
breaking approach used by Mendel and the intuitive and mathematical genius he brought
2. The story of Mendel and his work is a good opportunity to illustrate the scientific
3. Provide students with plenty of practice working simple genetics problems, preferably
in small groups.