I Gregor Mendel s Discoveries Breeded garden peas for heredity experiment A Experimental and Quantitative Approach 1865 The Father of Genetics Influences physicist Doppler and botanist Unger Helped spark interest in gene variation Total control over mating between flowers flowers self fertilize naturally Believed not medium between purple and white either or situation Focused on other aspects of plants such as seed weight etc This helped discover inheritance true breeding parents considered P generation first filial generation or the hybrid offspring are called F1 second filial generation is called the F2 F2 determined fundamental principles for heredity character heritable feature such as flower color in garden peas that varies trait each variety for a flower color such as purple and white true breeding when self fertilize produce same variety hybridization crossing of two true breeding varieties B The Law of Segregation a Allele pairs separate during gamete formation and randomly reform as pairs during the fusion of gametes at fertilization 1 Different Alleles cause the varied flower colors in the pea plants The gene is located on a specific locus on a specific chromosome On each chromosome the DNA for flower color is located in the same spot but the bases used to represent the trait may be different since the traits are different 2 For each character an organism inherits one from each parent which may be the same or differ 3 When alleles differ one is dominant and fully expressed in appearance The other is recessive and is not noticeable in appearance 4 Two alleles segregate during gamete production if each gamete receives the same allele the parent is true breeding if not the hybrids will have a 50 50 chance of either trait b Useful Vocabulary 1 homozygous identical alleles for a character PP pp 2 heterozygous two different alleles Pp 3 genotype genetic makeup 4 phenotype physical traits 5 Punnett Square a way of predicting the results of a genetic cross of a known genotype c The Testcross Breeding of a recessive homozygote with a dominant phenotype known genotype C The Law of Independent Assortment a Each allele pair separate independently during gamete formation when genes for two different characteristics are located on different pairs of homologous chromosomes 1 monohybrids F1 hybrids in which one follows only one character Rr 2 dihybrids heterozygous for both characters RrPp D Rules of Probability a The Rule of Multiplication b The Rule of Addition c Solving Genetic Problems E Behavior of a Gene II Extended Mendelian Discoveries A Relationship Between Genotype and Phenotype a Incomplete Dominance The two genes mix because neither is dominant or recessive Therefore both traits show up in the F1 generation as combination or intermediate trait Ex a red flower and a white flower produce a pink flower instead of just red and white flowers b Dominant Allele Dominance can occur in either a heterozygote or a dominant homozygote They do not cover one another up in the process of developing a phenotype Majority of the population has the recessive gene for number of finger which is 5 In codominance both genes are present in the phenotype As in blood there are three types A B and AB The phenotypes of both A and B are present in AB not mixed or changed in any way c Multiple Alleles Blood can has three genes that can make up four phenotypes A B AB and O O type blood being the recessive gene is represented by the ii There are antigens antibodies present in A and B blood that is not present in O Leaving it impossible to give an O patient blood other than O IAi IAIA IBi IBIB IAIB ii d Pleiotrophy A gene can affect more than one phenotypic effects Pleiotropic alleles mostly affect hereditary diseases such as sickle cell e Epistasis One gene alters the expression of another gene that was inherited independently f Polygenic Inheritance An additive effect of two or more gene loci on a single phenotype 1 Quantitative Characters A heritable feature in a population that varies continuously as a result of environmental influences and polygenic inheritance g Environmental Impact on Phenotype 1 Norm of Reaction range of possibilities for a single genotype as influenced by the environment 2 Multifactorial phenotype influenced by many factors including genes and environmental attributes h Heredity and Variation III Mendelian Inheritance In Humans A Pedigree Analysis A pedigree is a type of family tree where traits are followed from one generation to the next to analysis each dominant and recessive gene Predictions can be made by examining a pedigree Since a generation in a human family is about twenty years a pedigree has to include much of the past to make an accurate model B Human Disorders a Recessively Inherited Disorders These disorders are represented by aa versus a person lacking the disease is Aa or AA People who are Aa for a recessive gene are called carriers because they are likely to give that particular gene to their offspring 1 Cystic Fibrosis mucus accumulation in the lungs pancreas digestive tract and other organs Immune cells come to rescue but contribute to the buildup of mucus 2 Tay Sachs Disease a child has a dysfunctional enzyme that fails to break down brain lipids of a certain class causing accumulation in the brain Eventually causing death usually before four years of age 3 Sickle Cell Anemia the person has defective red blood cells and under extreme stress will not carry oxygen properly causing them to form sickle shapes b Dominantly Inherited Disorders 1 Achondroplasia a type dwarfism where a heterozygous people will have the phenotype because the gene is dominant 2 Huntington s Disease a fatal disease that destroys the nervous system but shows no signs until the mid 30s to mid 40s c Multifactorial Disorders C Technology a Carrier Recognition By taking various test heterozygous carriers can be distinguished from dominant homozygotes For disease such as Tay Sachs Sickle Cell and Cystic Fibrosis Carriers have the potential to give the recessive trait to their offspring increasing their chances of acquiring a fatal recessive disease b Fetal Testing 1 Amniocentesis During development a doctor can check for acquirement of a disease by inserting a long needle and extracting amniotic fluid for a karyotype This takes several weeks to complete 2 Chronic Villus Sampling CVS a tube can be inserted into the cervix to extract fetal tissues from the placenta for a karyotype This process
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