Ch 12 13 Patterns of Inheritance 11 07 2014 Ch 12 Mendel Genes Inheritance 11 07 2014 Sickle cell anemia develops when a person has received two mutated copies of a gene that codes for a subunit of hemoglobin Mutated gene codes for a slightly altered form of the hemoglobin subunit These cells tend to increase in and cluster at capillary openings obstructing flow of blood when oxygen is low Mendel used peas to study inheritance He discovered fundamental principles that govern inheritance 12 1 The Beginning of Genetics Mendel s Garden Peas Before scientists believed in blending theory of inheritance hereditary traits blend evenly in offspring through mixing of the parent s blood Mendel studied a variety of characters o Characters specific heritable attribute or property of an organism Mendel studied character differences or traits alternative forms of characters Mendel observed that many parental trait appear unchanged in offspring whereas others appear and disappear in other gens This was a result of segregation of chromosomes Mendel was innovative quantitative approach descriptive science and accepted practice He used cross fertilization pollen to fertilize came from a different plant True breeding pass traits w o change from one gen to the next P generation parental F1 generation the 1st gen of offspring between two true breeding parents F2 gen offspring of 1st gen Conclusion 1 the adult plants carry a pair of factors that govern the inheritance of each trait Genes are located on chromosomes Alleles different versions of a gene producing different traits of a character Diploids two copies of each gene Conclusion 2 if an individual s pair of genes consists of different alleles one allele is dominant over the other which is the recessive Dominance masking effect Conclusion 3 the pairs of alleles that control a character segregate as gametes are formed half the gametes carry one allele and the other half carry the other allele principle of segregation Homozygote true breeding individual w both alleles of a gene the same produces only one type of gamete Homozygous a homozygote individual Heterozygote individual w two different alleles of a gene produces two Heterozygous heterozygote individual Monohybrid F1 heterozygote produced from a cross that involves a single types of gametes trait Monohybrid cross cross between two individuals that are each heterozygous for the same pair of alleles 13 Introduction to Genetics 11 07 2014 I Basic Genetic Terms Basic foundations of classical genetics were established by Johann Gregor Mendel DNA deoxyribonucleic acid Basic genetic material Has 4 nucleotides Encodes to make RNA and protein Genes unit of heredity according to classical genetics based on the expression of a specific trait in successive generations of an organism May not have been isolated and characterized Sometimes used to refer to a locus Alleles alternate forms of a gene Responsible for a particular trait Present in two different chromosomes which are derived for mother and father May code for the same protein with slightly different amino acid sequences and may result in different traits May be exchanged during meiosis in the crossing over and recombination process Locus location of a gene or a few genes on a chromosome Used interchangeably w gene may be as long as 50 100 kb Genes coding for different traits may exist close to each other on a locus and are less likely to be separated during recombination Chromosomes are mapped w specific genes based on the frequency of recombination of known genes Chromosomes contain several hundreds of loci each Exist as loosely dispersed chromatin DNA proteins in interphase and condense into visible chromosomes during cell division Genotype assorted collection of various genes in the chromosomes represented by capital or small letters to notate dominant and recessive alleles resp Phenotype physical trait physiological condition or biochem aspect determined by the genes at the molecular lvl acc to its genotype Homozygous an organism w a pair of identical alleles for a particular gene in both the homologous chromosomes Heterozygous organism w mixed allele pairs for a particular gene Dominant allele allele of a gene that is expressed under both homozygous and heterozygous condition due to the DNA sequence of the particular gene and the nature of the protein coded by the gene Denoted in capital letters Recessive allele allele of a gene that is expressed only under Organism can be homozygous dominant AA homozygous recessive aa homozygous condition or heterozygous Aa II Mendel s Laws of Inheritance Reasons for success o Quantitative approach he used a mathematical approach to a biological problem one reason why his results were appreciated acknowledged o Good model system peas are easy to grow and hybridize to monitor o Selection of traits or phenotypes he chose phenotypes that easy to inheritance study Pure bred homozygous varieties parents F0 are crossed by hybridization fertilizing one plant s stigma w another plant s pollen A Law of segregation Allele pairs segregate separate during gamete formation and the paired condition is restored by the random fusion of gametes at fertilization Test cross done by hybridizing a parent of unknown genotype w a known homozygous recessive parent to find out the unknown genotype B Law of independent assortment Law the segregation of each allele pair is independent of other allele pairs The individual allele pairs need to be located on separate loci far from each other to allow independent assortment during gamete formation Dihybrid cross two different traits coded by two allele pairs Can be figured out using the rules of multiplication Alleles can segregate independent of each other and recombine to make new phenotypes III Complexities of Genetic Inheritance Intermediate inheritance or incomplete dominance the homozygotes have a particular phenotype and the heterozygotes have an intermediate phenotype meaning that no single gene is completely dominant Codominance both phenotypes are expressed about equal lvls by the expression of two types of proteins by two alleles Pleiotropy one gene or allele codes for more than one phenotype Epistasis one gene interferes w the expression of another gene Multiple genes some genes exist in more than two forms Sex linked inheritance phenotypes affected by genes located on sex chromosomes are expressed depending on the sex of the individuals X in male XY is referred to as