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• Compare your personal traits with your parents. Make a column for each. • What controls the inheritance of traits in organisms? • Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive. Mendelian Genetics • Genetics is the science of heredity. • Heredity is the passing on of genetic material and thus traits from parent to offspring. Gregor Mendel • Austrian Monk and science teacher 18221884 • Considered the “Father of Heredity” • He conducted plant breeding experiments in a monastery garden. • In 1865 he made his work public about heredity. Gregor Mendel • It took him 2 years to select the pea plant as his subject. • He collected data for 8 years. • His sample sizes were large; he tabulated results from 28,000 pea plants. • He repeated his experiments. • He analyzed his data with statistics (probability theory). • His work was not well known until early 1900s—34+ years later! Mendel observed seven pea traits that are easily recognized and apparently only occur in one of two forms: The trait on the left is dominant and the trait on the right is recessive. Some of his experimental procedure. Mendel’s Pea Plant Experiment 3.He Mendel Hecrossed recorded chose trueon 2.1. a data true 5.4.He recorded data on the He self pollinated breeding lines of the offspring thisa breeding plantofwith each plant/trait he F1) offspring of the second the F1 offspring cross (First Filial, plant of the opposite trait studied (true generation, calling it the or firstxgeneration. (purple white). breeding lines Second Filial always He calledproduced this the generation (F2) offspring of the Parental (P) generation. same type). Mendel’s Experiment In cross-pollinating plants thatgenerations either produce This 3:1 ratio occurs in later as However, the following generation (f2) yellow or green peasthat exclusively, well. Mendel realized this wasMendel the key to consistently has abasic 3:1 ratio ofgeneration yellow to found that the first offspring (f1) understanding the mechanisms of green. always has yellow peas. inheritance. He came to three important conclusions from these experimental results: 1.3. The inheritance of each trait isindividual determined A trait may not show up in an 2. An individual inherits one such unit from by "units" or "factors" that are passed on to but canparent still befor passed on to the next each each trait. descendents generation. unchanged (these units are now called genes). Mendel established three principles (or Laws of Genetics) from his research: 3. Principle of Independent Assortment 2. Principle of Segregation - the two factors 1.The Principle of Dominance and factors of a trait separate independently of one Chromosomes, genes, or DNA wasgamete not (alleles) for a trait separate during another during gamete (sex trait cell) division called Recessiveness one is masked known of during Mendel’s lifetime in the mid formation; the pair of alleles of each parent meiosis or covered up one by another trait. from each 1800s. separate and only allele passes Another way to look at this is, whether a We now know that there aresex parent on to an offspring. Neither did he know the process of how flower is purple has nothing to do with the length alleles (genes) that are more dominant Which allele in a parent's pair of alleles is cells (gametes) are made. of the plants stems - each trait is independently inherited is a matter of chance. than others. inherited. We now know that this segregation of alleles occurs during the process of sex cell (gamete) division (meiosis). Meiosis What are genes made of? • Chromosomes are made of DNA • Genes are located on Chromosomes • Genes are a section of DNA that codes information for making proteins. What are Genes? • A gene is a segment of DNA on a chromosome. • A gene codes for a specific trait. • Gene is inherited from the biological parents. Therefore, the traits of any organism is from the biological parents. • Genes come in pairs. What is a dominant gene? • The gene that expresses itself; the most powerful and dominant gene used by the cell. • It has the power to overshadow the recessive gene when there is complete dominance. • Some examples are: brown hair, right handed, etc. What is a Recessive Gene? • The gene that is overshadowed by a dominant gene • Recessive genes can only express themselves in the absence of the dominant gene. • A recessive trait can only show in a person with both genes in a pair are recessive genes. Genetic Terms to know • Gene- A sequence of base-pairs (ATCG) of various lengths that code for proteins. • Loci- Location of a gene on the chromosome. • Phenotype- Outward appearance of a trait, for example: hair color, size, horn shape. • Genotype- Genetic classification of a gene, AA, Aa, aa. Always come in pairs. • Homozygous- contains 2 identical genes for the same trait, AA, BB, cc – “Purebred” • Heterozygous- contains 2 different genes for the same trait, Aa, bB, Cc-- “Hybrid” Genotype • Genotypes of your body cells contain two copies of the gene. Aa or AA or aa However, Gamete (sex cells) genotypes contains only one copy (allele) of the gene. A or a Steps for Solving a Genetics Problem: • Trait – dominant = A (AA or Aa) • Trait – recessive = a (aa) Aa x ________ Aa • _______ =genotype A ____ ____ a • Punnett Square Parent A ____ AA Aa a ____ aa aA Parent • The Punnett Square diagram is used to see the probable outcome of a cross. Fill in the punnet square of this cross (fertilization). If a heteroyzous round seed is crossed with itself (Rr x Rr) a Punnett square can help you figure out the ratios of the offspring. Practice! Showing a genetic cross! Heterozygote cross: Rr x Rr R r R RR Rr r Rr rr What Do youpercentage see why of the offspring will 1 out of 4 dominant traits are probably have white or 25% more common? flowers? Offspring from a Collie Cross! Who has on thethe The dog dominant allele? lower left side What percentage of the offspring will probably have fur that is black and white? 50% Each parent has just one version of the gene in each of its sex cells. Not paired. It is random what each sex cell gets as the gene. The End! Using a PUNNETT SQUARE Finally, take each letter in each column and combine it with each letter from each row in the corresponding square. You should now have a picture close to this: Incomplete Dominance Pink A blend of dominant and recessive traits Dihybrid Cross: Punnett Square AB Ab aB ab AB ASBB ASBb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb Example 2: Answer the Question • What is the probable offspring phenotype ratio for a cross involving two parents that are heterozygotes for both traits? – 9/16 Pink, tall – 3/16 Pink, short – 3/16 Pink, tall – 1/16 White, short Incomplete Dominance: • Incomplete Dominance: is a condition in which the dominant allele cannot completely mask the expression of another allele. • For example, red-flowered snapdragons crossed with white ones yield pink in the first generation. • The heterozygote phenotype is somewhere between that of two homozygotes. Codominance • Codominance: is a condition in which both alleles are expressed in heterozygotes. • It is NOT a middle combination of two alleles like the red and white snapdragons make pink. • Instead it is where both alleles and their traits are both equally expressed. • Best example is blood type. IA and IB are each dominant to i (type O), but are codominant to each other. Therefore, some persons can express both genes and have AB blood. Mendel’s Experiment With all of the seven pea plant traits that Mendel Note that each of theappeared f1 generation plants over (shown examined, one form dominant the However, theadominant yellow allele does above) inherited Y allele from one parent and a other. Which is to say, it masked the presence of not alter green in any G allele from the recessive other. When the one f1 plants the other allele. For example, when the genotype breed, eachBoth hasalleles an equal of passing way. canchance be passed on to on for pea color is YG (heterozygous), the either Y or G alleles to each offspring. the next generation unchanged. phenotype is yellow.