Chapter Menu Lesson 1: Foundations of Genetics Lesson 2: Understanding Inheritance Click on a hyperlink to view the corresponding lesson.

4.1 Foundations of Genetics heredity genetics dominant recessive gene law of segregation law of independent assortment allele phenotype genotype homozygous heterozygous

Early Ideas About Heredity 4.1 Foundations of Genetics Early Ideas About Heredity Combined genetic material from a sperm and an egg determines the traits or features of an offspring. Heredity is the passing of traits from parents to offspring.

Early Ideas About Heredity (cont.) 4.1 Foundations of Genetics Early Ideas About Heredity (cont.) The idea of blending inheritance is offspring are a blend of genetic material from both parents. The genetic material mixed or blended like colors of paint. Over many generations, populations would eventually look alike. Blending inheritance cannot explain why some traits skip a generation.

Gregor Mendel and His Experiments 4.1 Foundations of Genetics Gregor Mendel and His Experiments Gregor Mendel was the first to record evidence that traits are determined by factors passed from parents to offspring. Mendel established the basic laws of heredity. Genetics is the study of how traits of organisms are passed from parents to offspring.

Mendel’s Experimental Methods 4.1 Foundations of Genetics Mendel’s Experimental Methods Mendel conducted breeding experiments by studying seven traits of pea plants and each traits had only two variations.

Controlled Experiments 4.1 Foundations of Genetics Controlled Experiments Mendel controlled fertilization in the pea plants, allowing him to see how traits pass from one generation to another. Mendel allowed some flowers to self-fertilize. He also performed cross-fertilization by transferring pollen from one pea flower to another.

Mendel’s Unique Methods 4.1 Foundations of Genetics Mendel’s Unique Methods Used true-breeding plants for each trait—plants that always produce offspring with that trait when they self-pollinate Recorded the inheritance of traits for several generations Used a mathematical approach

Mendel’s Experimental Results 4.1 Foundations of Genetics Mendel’s Experimental Results Mendel concluded that two factors control each inherited trait. When organisms reproduce, each gamete— sperm or egg—contributes one factor for each trait.

4.1 Foundations of Genetics Dominant Factors A genetic factor that blocks another genetic factor is called dominant. A dominant trait is observed when offspring have one or two dominant factors.

4.1 Foundations of Genetics Recessive Factors A genetic factor that is hidden by the presence of a dominant factor is recessive. A recessive trait can be observed only when two recessive genetic factors are present in offspring.

Mendel’s Laws of Heredity 4.1 Foundations of Genetics Mendel’s Laws of Heredity Law of segregation: the two factors for each trait segregate—separate from each other—during meiosis when gametes form Law of independent assortment: the factors for one trait separate independently of how factors for other traits separate

Modern Definitions of Mendel’s Ideas 4.1 Foundations of Genetics Modern Definitions of Mendel’s Ideas Mendel did not know about DNA or how cells reproduce, but his ideas about inheritance are still true today.

4.1 Foundations of Genetics Genes and Alleles A gene is a section of DNA that has information about a trait in an organism. Each form of a gene with different information is called an allele.

Genes and Alleles (cont.) 4.1 Foundations of Genetics Genes and Alleles (cont.)

Phenotype and Genotype 4.1 Foundations of Genetics Phenotype and Genotype The observable traits and all characteristics of an organism make up the organism’s phenotype. The alleles that make up an organism is the organism’s genotype. The alleles of a particular gene is that gene’s genotype.

Homozygous and Heterozygous Genotypes 4.1 Foundations of Genetics Homozygous and Heterozygous Genotypes Because eukaryotes have pairs of chromosomes, a genotype for a gene has two alleles. If the two alleles have the same information, the genotype is homozygous. If the two alleles have different information, the genotype is heterozygous.

Homozygous and Heterozygous Genotypes (cont.) 4.1 Foundations of Genetics Homozygous and Heterozygous Genotypes (cont.)

Law of Segregation Explained 4.1 Foundations of Genetics Law of Segregation Explained The movement of chromosomes during meiosis explains Mendel’s law of segregation. Each set of chromatids separates into different gametes during meiosis II. Each gamete receives only one allele.

Law of Segregation Explained (cont.) 4.1 Foundations of Genetics Law of Segregation Explained (cont.)

Law of Independent Assortment Explained 4.1 Foundations of Genetics Law of Independent Assortment Explained The daughter cells produced by meiosis receive only one chromosome from each pair of homologous chromosomes. A daughter cell might receive the A or a chromosome from pair 1 and the B or b chromosome from pair 2. This results in four possible allele combinations for two homologous pairs of chromosomes.

Law of Independent Assortment Explained (cont.) 4.1 Foundations of Genetics Law of Independent Assortment Explained (cont.)

Importance of Mendel’s Genetic Studies 4.1 Foundations of Genetics Importance of Mendel’s Genetic Studies In the 1860s, no one knew about chromosomes or meiosis so it was hard to understand Mendel’s discoveries. All the research of modern genetics is based on Mendel’s conclusions from his work with pea plants.

What is the passing of traits from parents to offspring called? 4.1 Foundations of Genetics What is the passing of traits from parents to offspring called? A inheritance B genetics C heredity D allele Lesson 1 Review

What are the alleles that make up an organism called? A genes 4.1 Foundations of Genetics What are the alleles that make up an organism called? A genes B genotype C phenotype D factors Lesson 1 Review

4.1 Foundations of Genetics If two alleles for a gene have the same information, what kind of genotype does that gene have? A homologous B recessive C heterozygous D homozygous Lesson 1 Review

End of Lesson 1

4.2 Understanding Inheritance Punnett square pedigree incomplete dominance codominance multiple alleles sex chromosomes polygenic inheritance genetic disorder

4.2 Understanding Inheritance Modeling Inheritance Two tools can be used to identify and predict traits among genetically related individuals. Punnett square pedigree Heredity

4.2 Understanding Inheritance Punnett Squares A Punnett square is a model used to predict possible genotypes and phenotypes of offspring. If the genotypes of the parents are known, the genotypes and phenotypes of the offspring can be predicted.

4.2 Understanding Inheritance One-Trait Model The Punnett square shows the possible offspring of a cross between two true-breeding pea plants—one with yellow seeds and one with green.

One-Trait Model (cont.) 4.2 Understanding Inheritance One-Trait Model (cont.) The only possible genotype for hybrid offspring is heterozygous—Yy. The phenotype will be yellow seeds because Y is dominant to y.

One-Trait Model (cont.) 4.2 Understanding Inheritance One-Trait Model (cont.)

4.2 Understanding Inheritance Two-Trait Model The possible offspring of two heterozygous genotypes—Yy and Yy—would have three different genotypes and two phenotypes.

4.2 Understanding Inheritance Pedigrees All the genetically related members of a family are part of a family tree. A pedigree shows genetic traits that were inherited by members of a family tree. Pedigrees are important tools for tracking complex pattern of inheritance and genetic disorders in families.

4.2 Understanding Inheritance Pedigrees (cont.) A pedigree chart that shows three generations of a family.

4.2 Understanding Inheritance Types of Dominance Alleles show incomplete dominance when they produce a phenotype that is a blend of the parents’ phenotypes. When both alleles can be observed in the phenotype, the interaction is called codominance. The human blood type AB is an example of codominance.

4.2 Understanding Inheritance Multiple Alleles Some genes have more than two alleles, or multiple alleles. The human ABO blood group is determined by multiple alleles as well as codominance. There are three different alleles for the ABO blood type—IA, IB, and i.

Multiple Alleles (cont.) 4.2 Understanding Inheritance Multiple Alleles (cont.)

Sex-Linked Inheritance 4.2 Understanding Inheritance Sex-Linked Inheritance Chromosomes X and Y are the sex chromosomes—they contain the genes that determine gender or sex. Except for sperm and eggs, each cell in a male has an X and a Y chromosome, and each cell in a female has two X chromosomes. A recessive phenotype is observed in a male when a one-allele gene on his X chromosome has a recessive allele.

Sex-Linked Inheritance (cont.) 4.2 Understanding Inheritance Sex-Linked Inheritance (cont.) In this family, the grandmother’s genome included the color blindness allele.

Polygenic Inheritance 4.2 Understanding Inheritance Polygenic Inheritance Polygenic inheritance is when multiple genes determine the phenotype of a trait. Many phenotypes are possible when possible when polygenic inheritance determines a trait.

4.2 Understanding Inheritance Maternal Inheritance Humans inherit mitochondrial genes only from their mothers. Inheritance of traits related to the mitochondria can be traced from grandmother to grandchildren. How are the traits of parents inherited and expressed in offspring?

Human Genetic Disorders 4.2 Understanding Inheritance Human Genetic Disorders If a change occurs in a gene, the organism with the mutation may not be able to function as it should. An inherited mutation can result in a phenotype called a genetic disorder.

Human Genetic Disorders (cont.) 4.2 Understanding Inheritance Human Genetic Disorders (cont.)

Genes and the Environment 4.2 Understanding Inheritance Genes and the Environment An organism’s environment can affect its phenotype. Genes affect heart disease, but so do diet and exercise. Genes affect skin color, but so does exposure to sunlight.

Punnett squares model the ____ of offspring. A genotypes B phenotypes 4.2 Understanding Inheritance Punnett squares model the ____ of offspring. A genotypes B phenotypes C genotypes and phenotypes D genes Lesson 2 Review

A incomplete dominance B codominance C multiple alleles 4.2 Understanding Inheritance What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes? A incomplete dominance B codominance C multiple alleles D polygenic inheritance Lesson 2 Review

How many Y chromosomes do females have? A 0 B 1 C 2 D 4 4.2 Understanding Inheritance How many Y chromosomes do females have? A 0 B 1 C 2 D 4 Lesson 2 Review

End of Lesson 2

Chapter Resources Menu Chapter Assessment California Standards Practice Concepts in Motion Image Bank Science Online Click on a hyperlink to view the corresponding feature.

A polygenic inheritance B sex-linked inheritance What is the term for the idea that offspring are a blend of genetic material from both parents? A polygenic inheritance B sex-linked inheritance C maternal inheritance D blending inheritance Chapter Assessment 1

What type of alleles can only be observed in the phenotype when they are present as a homozygous genotype? A dominant B recessive C inherited D heterozygous Chapter Assessment 2

A law of independent assortment B law of heredity C law of segregation What is the term for the idea that inheritance of one trait is not influenced by inheritance of another trait? A law of independent assortment B law of heredity C law of segregation D maternal inheritance Chapter Assessment 3

A color of camellia flowers B human AB blood type C color blindness What is a good example of a trait that is determined by multiple alleles? A color of camellia flowers B human AB blood type C color blindness D human ABO blood group Chapter Assessment 4

Why are male humans more likely to be color-blind than females? A maternal inheritance B sex-linked inheritance C polygenic inheritance D incomplete dominance Chapter Assessment 5

Which pea trait did Mendel not study? A seed color B pod color SCI 2.c Which pea trait did Mendel not study? A seed color B pod color C flower position D flower shape CA Standards Practice 1

SCI 2.d If two plants with genotypes Mm are crossed, what percent of the offspring will have phenotype M? A 0% B 25% C 75% D 100% CA Standards Practice 2

What is the term for when more than one gene determine a trait? SCI 2.c, 2.d What is the term for when more than one gene determine a trait? A incomplete dominance B multiple alleles C polygenic inheritance D sex-linked inheritance CA Standards Practice 3

Which does NOT describe Mendel’s experiments? SCI 2.d Which does NOT describe Mendel’s experiments? A Mendel observed several generations of plants. B Mendel chose pea plants because they reproduce quickly. C Mendel counted small numbers of offspring. D Mendel used true-breeding plants. CA Standards Practice 4

What type of genetic disorder is hemophilia? A dominant SCI 2.d What type of genetic disorder is hemophilia? A dominant B X-linked recessive C codominant D recessive CA Standards Practice 5

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