Lesson 6 Chapter 3 - Dr. Kurt Pontasch PDF

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Dr. Kurt Pontasch...

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Mendelian Genetics Lesson: 6 ❖ Genes - a portion of DNA that codes for a given polypeptide chain. ➢ Proteins control characteristic display, whether you’re a blonde, or brunette, or your tall or short, etc. ➢ Genetics is the study of how genes control these characteristics and how they are passed on from one generation to the next. ➢ First person to study the patterns of inheritance was an austrian monk named Johann Gregor Mendel. ➢ Mendel conducted a scientific experience on garden peas from 1856-1868. The laws he developed were not really accepted until the 1900’s. ➢ The patterns of inheritance that follow the law developed by Mendel are called Mendelian Genetics. ➢ Mendel thought the gene as a particle that is passed on from parent to offspring. ➢ These genes are actually specific sequences of DNA on the nucleotides ➢ All sexual reproducing organs are Diploids. * They have 2 sets of chromosomes, 1 from each parent. They have 2 sets of genes from each parent. ❖ Even though each individual has 2 genes for each characteristic, there may be several alternative form of each gene in a population. ➢ Alleles - one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. ➢ Genotypes - the genes you are stuck with. ■ That combination of gene that expresses itself is a Phenotype. ➢ There are 3 general typical for these alleles. ➢ Genotype: ■ Free - Free ■ Free - Attached ■ Attached - Attached ➢ For any particle pair of alleles in an individual the alleles are either identical or not identical. ➢ Homozygous Dominant, heterozygous recessive. ➢ Often 1 allele mask the effect of the other allele or a given trait. ■ The Allele that is masked and not expressed is the Recessive Allele ■ The Allele that is expressed in the DNA is the Dominant Allele. ■ The Recessive traits only express themselves when the traits are Homozygous Recessive. ❖ Mendel's Laws of Heredity - Mendel was the first person to develop a method for predicting the outcome of inheritance patterns. He was lucky because each characteristic that he picked was found on a separate chromosome. If the characteristic would have have been on the same chromosome, (those are called linked genes) he would not have seen the same patterns of the inheritance that he did. ➢ Heterozygous - Big Letter, little letter (Rr) ➢ It’s often practical to distinguish whether a given phenol type is heterozygous or

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homozygous for the given allele. ➢ Homozygous dominant breeds true. ➢ Testcross - useful for farmers and plant people that are looking for stalk that will breed true. Mendel formulated several laws of genetics which describes how traits are inherited and expressed. Mendel's Law of dominance - when an organism is heterozygous for a given trait, the allele that is expressed is said to be dominate, and the allele that is masked is said to be recessive. Mendel’s Law of Segregation - When gametes are formed by a diploid organism, the alleles that are controlled a given trait separate from each other into different gametes and retain their individuality. Mendel’s Law of independent assortment - members of one gene pair separate from each other independently from the members of other gene pairs. Probability vs. Possibility ➢ Probability - chance that an event will happen ■ Prob = # of events that produce one outcome divided by # of possible outcomes. ➢ Possibility - It’s possible to flip a coin and get 3 heads in a row. Monohybrid Cross - genetic cross that one generation of a single characteristic is passed down to the next generation. ➢ Know how to solve monohybrid Cross and Punnett squares***** ➢ He will give us a “Given” and we have to set it up. ■ Ex. Given - In humans, the free earlobes is dominant and attached earlobes is recessive. ■ Question: If both parents are heterozygous , what is the possibility they will have a child with free earlobes vs. attached earlobes ➢ 5 Basic steps. **** (goes with above question) ■ 1. Assign a symbol for each allele. A capital letter is Dominate, a lower case letter is a Recessive Allele E= free earlobe e= attached ■ 2. Determine the genotype of each parent and indicates a male? ■ 3. Determine all possible types of gametes and place them on a punnet square. Since both parents are heterozygous, they can both produce a big E and a little e. ■ 4. Determine all gene combination that can result when these gametes unite. (ex. Fill in the squares….. EE, Ee,Ee,ee. ) ■ 5. Determine the phenotype of each gene combination. (Example EE=Free Ee= Free Ee= Free ee= Attached) ■ So the initial answer is that the child will have a 75% or ¾ chance of having Free Earlobe. 25% ¼ chance of attached earlobes. ➢ This 3 to 1 Ratio is always expected in a monohybrid cross between two heterozygous parents**************...