Class Notes Genetic Definitions Trait = Any Characteristic that can be passed from parents to offspring Heredity The passing of traits from parent to offspring - Blood Type - Color of our Hair - Round Face - Curly Hair Think of a Trait that you is believe to be Inherited from Parent to Offspring. Listen Closely & Don t repeat a Trait someone else has previously said or is listed above. Genetics The Branch of Biology that Studies Heredity Gregor Mendel (1822-1884 ) The Father of Genetics Austrian Monk that experimented with pea plants First to predict rules that accurately predicted patterns of heredity Why Pea Plants were a good subject for studying heredity: 1.They have many traits that have two clearly different forms Seed color is either Yellow or Green
2. Mating of Garden Pea Flowers can be easily controlled Self-Fertilization: You can allow the flower to fertilize itself Cross-Pollination: You can transfer the pollen to another flower on a different plant 3. The Garden Pea Plant is: Small Grows easily Matures quickly Produces many offspring Thus results are obtained quickly Seven Traits Mendel Studied: Seed Shape - Round / Wrinkled Seed Color - Yellow / Green Seed Coat Gray / White Pod Shape - Smooth/ Constricted Pod Color - Green / Yellow Flower Position - Axial / Terminal Plant Height - Tall / Short Gene: When egg and sperm cells form, only one of the two factors for each trait is given to a gamete When two gametes fuse during fertilization, the resulting offspring has two factors for each trait These factors are called GENES For each inherited trait, an individual has two copies of the gene - one from each parent Allele = Different versions of the gene When two different alleles occur together, one of them may be expressed and the other may have no observable effect Dominant Trait = The trait that is expressed Recessive Trait = The trait that is not expressed when the dominant form of the trait is present
The hand of blues guitar player Hound Dog Taylor exhibits Polydactyly Having more than five fingers is Controlled by a Dominant Allele Dominant doesn t mean the trait is more frequent in a population Note: A gene is really a segment of DNA on a chromosome that codes for a specific protein The Dominant Allele says: Make Protein X The Recessive Allele says: Do Not make Protein X Letters are used to represent Alleles Dominant alleles are indicated by writing the first letter of the trait as a capital letter Example: Yellow Seed Color = Y Recessive alleles use the first letter of the dominant trait, but the letter is lower case Example: Green Seed Color = y Another Example: (In Cats) if Yellow is Dominant = & if Gray is Recessive = A Gene has 2 Alleles: YY is a Cat is a Cat is a Cat Another Example: (In Cats) if Yellow is Dominant = Y & if Gray is Recessive = y A Gene has 2 Alleles: YY is a Yellow Cat is a Yellow Cat is a Gray Cat An organism is Homozygous or Purebred for a trait if both alleles are Identical Gray is Recessive YY Yellow is Dominant
An organism is Heterozygous or Hybrid for a Trait if the Alleles are NOT Identical Genotype = (The Symbols) The set of Alleles an organism has Gray Yellow is Dominant so the trait is expressed is Recessive so the trait is not expressed YY or Phenotype = (the physical appearance) The form or color of that trait that is observed Yellow Gray Law of Segregation: The Law states that: The two alleles for a trait segregate when gametes are formed This is because during meiosis i the homologous chromosomes are separated Law of Independent Assortment: The Law states that: The alleles of different genes separate independently of one another during gamete formation This is because the genes are on different chromosomes, so they are not connected to each other Monohybrid Cross A genetic cross involving ONE trait (a One-Factor Cross) Dihybrid Cross A genetic cross involving TWO traits ( a Two-Factor Cross)
Punnett Square = A diagram that predicts the expected outcome of a genetic cross by considering all possible combinations of gametes in the cross Heterozygous x Heterozygous x Y y Y YY y The End