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

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

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

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

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

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. 4.2 Understanding Inheritance –The human blood type AB is an example of codominance.

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. 4.2 Understanding Inheritance

Multiple Alleles (cont.) 4.2 Understanding Inheritance

Sex-Linked Inheritance Chromosomes X and Y are the sex chromosomes—they contain the genes that determine gender or sex. 4.2 Understanding Inheritance 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 In this family, the grandmother’s genome included the color blindness allele.

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

Maternal Inheritance Humans inherit mitochondrial genes only from their mothers. 4.2 Understanding Inheritance 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 If a change occurs in a gene, the organism with the mutation may not be able to function as it should. 4.2 Understanding Inheritance An inherited mutation can result in a phenotype called a genetic disorder.

Human Genetic Disorders (cont.) 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. 4.2 Understanding Inheritance

Lesson 2 Review Punnett squares model the ____ of offspring. Agenotypes Bphenotypes Cgenotypes and phenotypes Dgenes 4.2 Understanding Inheritance 1.A 2.B 3.C 4.D

Lesson 2 Review What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes? Aincomplete dominance Bcodominance Cmultiple alleles Dpolygenic inheritance 4.2 Understanding Inheritance 1.A 2.B 3.C 4.D

Lesson 2 Review How many Y chromosomes do females have? A0A0 B1B1 C2C2 D4D4 4.2 Understanding Inheritance 1.A 2.B 3.C 4.D