Biology+DNA

Dominant - the allele/trait that shows up Recessive - the allele/trait that is hidden Incomplete Dominance - truth at the molecular level Codominance - a trait that shows both at the same time Multiple Alleles - more than 2 allele choices Polygenic traits - eye color Episasis - one gene influences the behavior of other genes Pleiotropy - one gene with multiple traits

Every living thing plant or animal has a set of characteristics inherited from its parent or parents. The delievery of characteristics from parents to offspring is called heredity.

Studying of heredity or //gentics// is the key to understanding what makes each organism unique. The modern science was founded by Gregor Mendel. Mendel was a monk in charge of the garden. In his garden he did work that changed biology forever.

Mendel used garden peas to experiemtn. A single pea plant can produce hundreds of offspring. Peas are used today as a "model system" Scientist use model system because they are convient to study and tell us how other organism are able to function. Using peas in a time period of 1 or 2 seasons, was able to perform experiements that would have taken decades with pigs, horses, or other large animals.

Mendel's garden had several stocks of pea plants and were "true-breeding" meaning they were self pollinating and would produce offspring identical to themselves. The traits of each successive generation would be the same. //Trait-// a specific characteristic, such as seed color or plant height, of an individual.

Many traits vary from one individual to another. Ex. one stock of Mendel's seeds produced only tall plants, while another produced shorts ones. Another one produced only green seeds while another stock produced yellow seeds.To figure out how traits were determined, Mendel would take one plant and reproduce with another kind of plant. This showed 7 different traits of pea plants, each of them had 2 contrasting characteristics, like green seeds and yellow seeds. Mendel then breeded plants with each of the 7 contrasting characteristics and studied their offspring. //Hybrids -// the offspring of crosses between parents with different tratis. An individual's characteristics are determined by factors, that are passed from one parental generation to the next. Today scientist call the factors taht are passed from parent to offspring //genes//.

Punnett Squares- Mendel realized that the principle off probablilty could be used to explain the results of his gentic crosses. //Probability - **the chances of a particular event will occur. Phenotype - physical traits of an organism Genotype - the genetic makeup.**// Punnett Squares use mathematical probaility to help predict the genotype and phenotype combinations in genetic crosses.



Summary of Mendel's Principles

Enviromental conditions can affect gene expression and influence genetically determined traits
 * Mendel's principles of heredity, observed through patterens of inheritance, form the basis of mondern genetics.**
 * The inheritance of biological characteristics is determined by individual units called genes, which are passed from parents to offspring.
 * Where two or more forms (alleles) of the gene for a single trait exist, some allels may be dominant and other may be recessive.
 * In most sexually reproducing organisms, each adult has two copies of each gene - one from each parent. These genes segregate from each other when gametes are formed.
 * Alleles for different genes usually segregate independently of each other

How many sets of genes are found in most adult organisms? First, an organism with two parents must inherit a single copy of every gene from each parent. Second, when that orgnaism produces gametes, those two sets of genes must be separated so that each gamete contains just one set of genes. //Homologous// - each of the four chromosomes from the male parent has a corresponding chromosome from the femail parent. //Diploid -// a cell that contains both sets of homologous chromosomes or "two sets" //Haploid -// Some cells contain only a single set of chromosomes and a single set of genes or "one set"
 * The diploid cells of most adult oranismss contain two complete sets of inherited chromosomes and two complete sets of genes.**

Phases of Meiosis Meiosis I

//Prophase I -// after interphase I, the cell begins to divide and the chromosomes pair up. In prophase I of meiosis, each replicated chromosome pairs with its corresponding homologous chromosome. This pairing forms a tetrad, containing four chromatids, then forming a process called //crossing-over.// Crossing over produces new combination of alleles in the cell.

// Metaphase I and Anaphase I -// As Prophase I ends, a spindle forms and attaches to each tetrad. During metaphase I of meiosis, paired homologous chromosomes line up across the center of the cell. As the cell moves into anaphase I, the homolougs pairs of chromosomes seperate.

During Anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. //Telephase I and Cytokinesis// - When anaphase I is complete, the separated chromosomes cluster at opposite ends of the cell. The next phase is telphase I, in which a nuclear membrane forms around each cluster of chromosomes. Cytokinesis follows telophase I, forming two new cells. Meiosis I results in two cells, called daughter cells but because each pair of homologous chromomsomes were seperated, neither daughter cells has two complete sets of chromosomes that it would have in a diploid cell. The two cells produced by meiosis I have sets of chromosomes and allels that are different each other and from the diploid cell that entered meiosis I.


 * //Meiosis II -//** the two cells now enter a second meiotic division, but doesnt go through a round of chromosome replication before entering meiosis II.

//Prophase II -// As the cells enter prophse II, there chromosomes - each consisting of two chromatids - become visible. They dont pair to form tetrads, because the homologous pairs were already separated during meiosis I.

//Metaphase II, Anaphase II, TelophaseII, and Cytokinesis -// During metaphase of meiosis II chromosomes line up in the center of each cell. As the cell enters anaphase, the paired chromatids separate. Each of the four daughter cells produced in meiosis II receive two chromosomes. These four daughter cells now contain the haploid number (N) - just two chromosomes each.
 * The final four phases of meiosis II are similar to those in meiosis I. However, the result is four haploid daughter cells.**