Genética Y Herencia PDF

# GENÉTICA Y HERENCIA ## Introduction * When constructing a family tree, you can see that children possess some traits from their mother and some from their father. * Some traits might disappear in one generation and reappear in the next, such as a characteristic that resembles a grandparent. * W...

# GENÉTICA Y HERENCIA ## Introduction * When constructing a family tree, you can see that children possess some traits from their mother and some from their father. * Some traits might disappear in one generation and reappear in the next, such as a characteristic that resembles a grandparent. * What is inherited can be influenced by the environment in which the individual develops. ## Heredity * Inherited characteristics are carried in DNA and passed down through generations. * Genetics is a branch of biology that studies these mechanisms of transmission. * Each gene is a fragment of DNA. * Several genes are grouped together in one chromosome, like chapters in a book. ## Chromosomes * Most cells have two copies of each chromosome. These cells are called diploid. * Gametes, the egg and sperm cells, are haploid, meaning they have only one copy of each chromosome. * Each person inherits two versions of each gene, one from the mother and one from the father. ## Homozygous and Heterozygous * Each chromosome possesses a set of genes. * There is a second chromosome that contains a "set of genes" with the same characteristics. These are called homologous chromosomes. * A pair of genes that controls a trait is called an *alelo*. * An individual's set of genes is called a *genotype*. * An individual's physical and behavioral characteristics, including environmental influences, are called a *phenotype*. ## Cariotipo * Different staining techniques allow chromosomes to be visualized with a microscope. * A photograph of these chromosomes is called a *cariotipo*. ## Gregor Mendel * Gregor Mendel studied the inheritance of traits in pea plants. * He discovered that there were two alternative forms of a trait, such as green or yellow peas. * Mendel used *pure lines* in his studies, which is one form of a trait that is reliably passed down between generations. ## Dominant and Recessive Traits * Mendel noticed that one trait always appeared in the first generation of offspring (F1). He called this trait a *dominant trait* and the hidden trait a *recessive trait*. * For example, yellow peas are dominant to green peas. * **Example of Dominant Recessive Trait Inheritance:** * In a cross-breed between a plant with yellow peas (**AA**) and a plant with green peas (**aa**), the F1 generation will all have yellow peas (**Aa**). ## The Second Experiment * Mendel wondered if the recessive trait disappeared in F1, but it reappeared in the second generation (F2). * **Example of F2 Trait Inheritance:** * When the F1 generation, possessing yellow peas, is crossed with each other (**Aa** x **Aa**), the F2 generation (**AA, Aa, Aa, aa**) will have a 3:1 ratio of yellow peas to green peas. ## Gene Characteristics * Mendel determined that each characteristic was controlled by two copies of a gene, or *factors* that determined that trait. * He determined that each gene is responsible for a possible alternative for the trait. * He designated dominant traits with uppercase letters and recessive traits with lowercase letters. ## Genotypes * Based on whether the genes are dominant or recessive, there are three possible genotypes for a trait: * **AA** (homozygous dominant) * **aa** (homozygous recessive) * **Aa** (heterozygous) # Problems 1. In a certain plant, blue flowers are dominant (A), and white flowers are recessive (a). How will the offspring look if you cross blue flowers (homozygous) with white flowers (homozygous)? * **Parents:** **AA** x **aa** * **Gametes:** A a * **F1: Aa** * **Phenotype:** 100% of the offspring will have blue flowers. * **Genotype:** 100% of the offspring will be heterozygous. 2. In humans, widow's peak hairline is dominant (W) and a straight hairline is recessive (w). What will the offspring look like if a homozygous dominant (WW) male is crossed with a homozygous recessive (ww) female? 3. In pea plants, tall stems are dominant (T) and small stems are recessive (t). If a homozygous dominant (TT) plant is crossed with a recessive (tt) plant, what are the phenotypic and genotypic proportions of the offspring? * **Parents:** TT x tt * **Gametes:** T, t * **F1:** Tt * **Phenotype:** 100% of the offspring will be tall. * **Genotype:** 100% of the offspring will be heterozygous.