Genetics True or False Genes are things you wear on your legs. A priest raising peas in his garden was one of the first to discover how genetics works. Plants can be purebred just like dogs. Dominate alleles are larger than recessive alleles. The phenotype of an organism is what that organism looks like. Your genotype refers to the type of genes you re wearing. If you plant yellow pea seeds, you will have a plant that grows yellow peas. Meiosis plays a large part in what you look like. Genetics Vocabulary Heredity Genetics Traits Purebred Hybrid Genes Alleles Dominate allele Recessive allele Phenotype Genotype Homozygous Heterozygous Objectives Section 1 Mendel and His Peas Explain the relationship between traits and heredity. Describe the experiments of Gregor Mendel. Explain the difference between dominant and recessive traits. 1
Section 1 Mendel and His Peas Who Was Gregor Mendel? Section 1 Mendel and His Peas Cross and self fertilization Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant. Gregor Mendel was born in 1822 in Heinzendorf, Austria. At age 21, Mendel entered a monastery. He performed many scientific experiments in the monastery garden. Mendel discovered the principles of: heredity, the passing of traits from parents to offspring. Mendel s Experiments Gene=a section of DNA that codes for a trait Trait= physical characteristic flower color Alleles=different forms of a gene purple or white flowers 2
Recessive allele=this trait is covered up when a dominate allele is present Dominate allele= this trait always shows up when present Genotype= genetic makeup of an organism Phenotype- Physical appearance or form of an organism Genotype=WW Genotype=ww Phenotype=purple Phenotype=white Genotype=Ww Phenotype=purple Genotype=Ww Phenotype=purple Flower color genotypes and phenotypes W=purple w=white Genotype Phenotype Incomplete dominance neither gene is dominant Heterozygous Homozygous Dominant Homozygous Recessive 3
Codominance both alleles show separately Red and white hair The Chicken Coop Homozygous Cross W=Purple w=white 4
Heterozygous Cross Monohybrid Cross 1 Trait Plant height T=Tall t=short Heterozygous Heterozygous Genotype Ratio Phenotype Ratio Section 2 Traits and Inheritance What Are the Chances? Probability is the mathematical chance that something will happen. Probability is most often written as a fraction of percentage. 5
Calculating Probability Section 2 Traits and Inheritance Section 2 Traits and Inheritance What Are the Chances?, continued Genotype Probability To have white flowers, a pea plant must receive a p allele from each parent. Each offspring of a Pp Pp cross has a 50% chance of receiving either allele from either parent. So, the probability of inheriting two p alleles is 1/2 1/2, which equals 1/4, or 25%. Dihybrid Cross 2 Traits Seed color Y=Yellow y=green Seed shape R=Round r=wrinkled Dihybrid heterozygous cross YyRr Y y R r 6
Asexual Reproduction In asexual reproduction, only one parent cell is needed. The structures inside the cell are copied, and then the parent cell divides, making two exact copies. This type of cell reproduction is called mitosis. Most of the cells in your body and most single-celled organisms reproduce this way. Sexual Reproduction In sexual reproduction, two parent cells (sex cells) join together to form offspring that are different from both parents. Chromosomes that carry the same sets of genes are called homologous chromosomes. Each sex cell has only one of the chromosomes from the homologous pair. Sexual Reproduction, continued Genes and Chromosomes Walter Sutton studied meiosis in sperm cells in grasshoppers. Using his observations and his knowledge of Mendel s work, Sutton proposed that: Genes are located on chromosomes. 7
Meiosis and Mendel The steps of meiosis explain Mendel s results. The following slide shows what happens to a pair of homologous chromosomes during meiosis and fertilization. Meiosis and Mendel, continued Sex Chromosomes carry genes that determine sex. Human females have two X chromosomes. Human males have one X chromosome and one Y chromosome. 8
Meiosis and Mendel, continued Sex-Linked Disorders The genes for certain disorders, such as colorblindness, are carried on the X chromosome. Genetic Counseling Genetic counselors use pedigrees to trace traits through generations of a family. These diagrams can often predict if a person is a carrier of a hereditary disease. Selective Breeding In selective breeding, organisms with desirable characteristics are mated. 9