Chapter Introduction How are traits passed from parents to offspring?

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

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

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 What Controls Traits

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

Lesson 2

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

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

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

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

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

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

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

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

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

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

Lesson 2 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. Genes and the Environment

Lesson 2 The genes for traits are located on chromosomes.

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

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

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

Lesson 2 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?