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Genetics Where do you think the directions for making you came from?" Inheritance: what makes youYOU! Inheritance occurs through sexual reproduction. During sexual reproduction, a cell that contains genetic information from the mother and father join to form a completely new cell. Each parent organism contains one-half of the genetic material need to create a new organism. DNA Stands for: Deoxyribonucleic acid It is where genetic information is stored. It determines every inherited physical characteristics of every living thing. It controls how the cell replicates and functions. What is a Gene? A short unit of DNA that codes for a particular trait, like a recipe. Genes are responsible for the inherited characteristics that distinguish one individual from another. Genes for a specific trait come in pairs. There are approximately 30,000 genes in each cell of the human body. The combination of all genes make up the blue print for the human body and its functions A person’s genetic makeup is called a genotype The physical expression of genes is called phenotype. Juicy Science Question? What would happen if something went wrong in the DNA sequence? Chromosomes In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Chromosomes come in pairs. Each member in the pair is called a homolog, or sister chromatid. Genes have a specific location on the chromosome. What is an Allele? One gene from the pair of homologs is called an Allele. An alternate form of a specific gene. For example, one homolog of a chromosome may have an allele for Regular height (A) and the other homolog May have an allele for short height (a). The alleles on a pair of homologs may or may not be different. Chromosome Number Each species has a characteristic number o chromosomes. Chimpanzees: 24 chromosome pairs Fruit flies have 4 chromosome pairs Humans have 23 chromosome pairs Heredity is the passing of traits from one generation to another. Heredity determines certain specific characteristics of plants and animals. Animals can inherit behavioral, mental, and physical traits. Another word for heredity is inheritance. Inherited Traits Characteristics that are passed from parent to offspring. For example: Eye color Eye shape Hair type Face shape Some traits are dominant and some are recessive. Dominant Traits A trait that will always be expressed in the phenotype. These are represented by CAPITAL letters. For example, A. Content Check What is the difference between phenotype and genotype? Phenotype= physical characteristic displayed. Ex, eye color Genotype= Set of genes carried by an organism Recessive Trait A trait that will only be expressed in the phenotype if two recessive alleles are present. Represented by lowercase letters. For example, a. The genotype aa would express the recessive trait. IN THE PRESENCE OF A DOMINANT TRAIT, THE RECESSIVE TRAIT WILL NOT BE EXPRESSED. Sex Linked Traits Males have an XY chromosome combination Females have an XX chromosome combination Genes that are carried by either sex chromosome are said to be sex linked X-linked diseases usually occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease. Austrian Monk & the “father” of genetics Before he became a Monk, he attended university to study science and Math. He studied pea plants to prove the existence of genes. He hypothesized that genes Controlled several different traits: Height, seed shape, seed color, and flower color are a few examples. Punnett Squares Mendel observed seven traits in pea plants. Mendal realized that each plant must have “two factors” for each possible trait, one factor from each parent. Some traits like dwarf height could be masked. (recessive) A Punnett square helps diagram the probability of each possibility genotype and phenotype in a generation. Mendel described the pea plant factors as alleles Punnett Squares In a Punnett square, the top of the table shows the alleles provided by one parent. The alleles for the other parent are placed along the left side of the table. One allele from each parent is placed in the individual squares, forming a new gene pair. The individual squares show the possibilities of allele pairs in the offspring. Punnett Square Example The cross Tt x tt: t t T Tt Tt t tt tt As the Punnett square shows, TT, Tt, and tt are all possible genotypes for the height of the offspring. The offspring with the genotypes TT and Tt will have a phenotype of tall; the offspring with the genotype of tt will have a phenotype of short. If the two alleles are the same (TT or tt), the genotype is considered purebred. If the two alleles are different (Tt), the genotype is considered hybrid. This example shows the inheritance of a single characteristic (height). A cross that shows the inheritance of a single characteristic is known as a monohybrid cross. It is sometimes difficult to predict certain traits in humans (for example hair color or eye color) because there may be several different genes that control these traits.