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 - a segment of DNA that codes for a specific trait 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 Definitions Abbreviations Phenotype Homozygous Dominant 2 Dominant Alleles FF Freckles

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

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

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/mixedtwins.asp

Mendel Unit 9, Part 2 Notes