Chapter 11 Introduction to Genetics Mendel Gregor Mendel

Chapter 11 Introduction to Genetics Mendel

Gregor Mendel (1850) �Did extensive studies on pea plant traits �Documented traits and inheritance patterns of thousands of plants �Keep in mind that DNA had not been discovered What he called “factors” we know to be genes, which code for particular traits

Monastery Garden Work �Mendel was in charge of the garden He really liked pea plants ▪ He had a stock of TRUE BREEDING plants ▪ If allowed to self pollinate they would always produce offspring identical to themselves ▪ However pea plants can also cross pollinate ▪ Mendel controlled this to produce certain TRAITS (specific characteristics)

Basic Terminology � Genetics – the study of heredity � Heredity – the passing of traits from parents to offspring � Trait – any characteristics that can be passed from parents to offspring examples: dimples & freckles � Genes - trait a segment of DNA that codes for a specific � Hybrid – cross between parents with different traits

Alleles � Alleles are slightly different forms of a gene The sequence of nitrogen bases may be slightly different A person has 2 alleles for each trait � Occur on homologous chromosomes � Of the 2 alleles, you receive one from your mother and one from your father during fertilization

Types of Alleles �Dominant Allele – the allele that is expressed; the stronger allele Symbolized by a capital letter �Recessive Allele – the allele that is only expressed if two of them are present; weaker allele Symbolized by a lower case letter

Types of Alleles �Example: Freckles = Dominant No Freckles = Recessive ▪ Dominant Allele = F ▪ Recessive Allele = f Dimples = Dominant No Dimples = Recessive ▪ Dominant Allele = D ▪ Recessive Allele = d

Genotypes & Phenotypes �Genotypes are the genetic make-up of an organism What do the alleles look like: ▪ DD ▪ Dd ▪ dd �Phenotypes are the physical appearance of a trait sometimes appear different due to environmental factors ▪ ▪ having dimples having freckles no dimples no freckles

Genotypes & Phenotypes Genotypes Homozygous Dominant Definitions Abbreviations Phenotype 2 Dominant Alleles FF Freckles

Genotypes & Phenotypes Genotypes Definitions Abbreviations Phenotype Homozygous Dominant 2 Dominant Alleles FF Freckles Heterozygous 1 Dominant Allele; 1 Recessive Allele Ff Freckles

Genotypes & Phenotypes Genotypes Definitions Abbreviations Phenotype Homozygous Dominant 2 Dominant Alleles FF Freckles Heterozygous 1 Dominant Allele; 1 Recessive Allele 2 Recessive Alleles Ff Freckles ff No Freckle Homozygous Recessive

Principles of Mendel �Mendel develop 3 principles that hold true today Principle of Dominance and Recessiveness Principle of Segregation Principle of Independent Assortment

Principles of Mendel �Principle of Dominance and Recessiveness One factor in a heterozygous pair may mask the other factor The factor that is expressed is dominant, the one that is masked (not expressed) is recessive In order for a recessive trait to be expressed, the organism must have a homozygous recessive genotype

Principles of Mendel �Principle of Segregation Gametes (sperm and egg) are formed during the process of meiosis Each gamete receives only one allele for each trait

Principles of Mendel �Principle of Independent Assortment Alleles segregate into gametes randomly and independently of each other Therefore each egg (or sperm) cell should be different from the another egg (or sperm) cell �http: //www. snopes. com/photos/people/mixe dtwins. asp

Unit 9, Part 2 Notes Mendel