Chapter Introduction

1. How are traits passed from parents to offspring? Chapter Introduction

2. Understanding Inheritance • What determines the expression of traits? • How can inheritance be modeled? • How do some patterns of inheritance differ from Mendel’s model? Lesson 2 Reading Guide

3. Understanding Inheritance • gene • allele • phenotype • genotype • homozygous • heterozygous • Punnett square • incomplete dominance • codominance • polygenic inheritance Lesson 2 Reading Guide - Vocab

4. What Controls Traits • Mendel concluded that two factors—one from each parent—control each trait. • Mendel’s “factors” are part of chromosomes which exist as pairs—one chromosome from each parent. • Each cell in an offspring organism contains chromosomes from both parents. Lesson 2

5. What Controls Traits(cont.) • A gene is a section on a chromosome that has genetic information for one trait. • The different forms of a gene are called alleles. Each chromosome has one allele for every gene on it. • The two chromosomes in an offspring cell may have the same or different alleles. Lesson 2

6. Lesson 2

7. What Controls Traits(cont.) • Geneticists call how a trait appears, or is expressed, the trait’s phenotype. • The two alleles that control the phenotype of a trait are called the trait’sgenotype. Lesson 2

8. What Controls Traits(cont.) phenotype from Greek phainein, means “to show” Lesson 2

9. What Controls Traits(cont.) • When the two alleles of a gene are the same, the genotype is homozygous. • If the two alleles of a gene are different, the genotype is heterozygous. Lesson 2

10. What Controls Traits(cont.) Scientists use uppercase and lowercase letters as symbols to represent the alleles in a genotype. How do alleles determine the expression of traits? Lesson 2

11. Modeling Inheritance A Punnett square is a model used to predict possible genotypes and phenotypes of offspring. Lesson 2

12. Modeling Inheritance (cont.) A pedigree shows phenotypes of genetically related family members. Lesson 2

13. Modeling Inheritance (cont.) How can inheritance be modeled? Lesson 2

14. Complex Patterns of Inheritance • Sometimes traits appear to be blends of alleles. • Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes. • Codominance occurs when both alleles can be observed in a phenotype. Lesson 2

15. Complex Patterns of Inheritance (cont.) Some traits, such as human ABO blood type, are determined by more than one allele. Lesson 2

16. Complex Patterns of Inheritance (cont.) Polygenic inheritance occurs when multiple genes determine the phenotype of a trait. How does polygenic inheritance differ from Mendel’s model? Lesson 2

17. Genes and the Environment • An organism’s environment can affect its phenotype. • Some examples of environmental factors that affect phenotype are soil type that a flower is growing in or time of year that a butterfly develops. Lesson 2

18. The genes for traits are located on chromosomes. Lesson 2

19. Geneticists use Punnett squares to predict the possible genotypes and phenotypes of offspring. • In polygenic inheritance, traits are determined by more than one gene and have many possible phenotypes. Lesson 2

20. What is the name for different forms of a gene? A. alleles B. phenotypes C. genotypes D. chromosomes Lesson 2

21. What is the genotype when two alleles of a gene are the same? A. heterozygous B. dominant C. homozygous D. recessive Lesson 2

22. What occurs when both alleles can be observed in a phenotype? A. incomplete dominance B. homozygous C. polygenic D. codominance Lesson 2

23. 3. All inherited traits follow Mendel’s patterns of inheritance. 4. Scientists have tools to predict the form of a trait an offspring might inherit. Do you agree or disagree? Lesson 2