Essentials of Physical Anthropology Study Set 2
Quiz 4 :
Heredity and Evolution
Mendelian traits are the traits or characters which are controlled by alleles present at one genetic locus. These Mendelian traits have phenotypic expressions. Mendelian inheritance is that when a child receives a dominant allele from the parent, then he will possess dominant phenotypic trait and the child which receive recessive allele show recessive phenotype. This is the Mendel principle of genetic inheritance. ABO antigens are the antigens which are expressed on blood cells and circulate blood plasma. ABO system is the best example showing Mendelian inheritance. It is the blood group antigen system. This system is governed by the three alleles which are A, B, and O. they are present at the locus on ninth chromosome. These alleles produce antigens on the surface of red blood cells. The O allele is recessive to both A and B allele. The blood type varies in accordance with the antigen present, as described below. 1. If antigen is A, blood group is A. 2. If antigen is B, blood group is B. 3 If antigens are both A and B, blood group is AB. 4. When neither of antigens is present, blood group is O. In the ABO system, the four phenotypes (A, B, AB and O) are completely different from each other. Antigens are found on the red blood cell surface, while antibodies in the plasma. The table given below describes the ABO genotypes and associated phenotypes. If the two individual have phenotype A and Genotype AO, then there will be two alleles that is A and O of each parent. On crossing over, children's formed will be AA, AO, AO and OO. Thus, 75% children will have phenotype A and 25% will have phenotype O, that is one-fourth of the children of the above phenotypes will have blood group O.
Evolution of various species and the beginning of life on the Earth has been the topic of considerable debates over the decades. Many evolutionary biologists and paleontologists have the view that random mutations and asteroid strikes had changed and create a whole new different set of life on earth. The biggest question of evolution is the trajectory of chance and random mutations, which has taken place. It is nearly impossible to recreate these conditions in a laboratory. There are important questions in evolutionary biology, such as where exactly did the first cell originate and what can we tell more about our ancestor species. The discovery that the biomolecule RNA (ribonucleic acid) can self-replicate has caused a paradigm shift in the DNA (deoxyribonucleic acid) world hypothesis. More biologists are now of the view that RNA can self-replicate, which leads to another question in biology as, to which came first RNA or protein (both have an interdependent relationship for their production). Another fallacy of Darwinian evolution has been its failure to address the presence of fossils that are at the interface of two different epochs. This effectively means there have been extended periods of time in between two epochs without much happening.
Sickle cell disease is a genetic aberration leading to the formation of deformed RBC's (Red blood cells). Hemoglobin is the main oxygen carrier protein in the blood. It has a quaternary protein structure under normal conditions. People suffering from sickle cell disease have hemoglobin molecules which adhere to each other leading to the formation of fibers. This stickiness of proteins lead to the loss of structure of RBC's, which make them sickle shaped. A multitude of cardiovascular disorders can arise due to this abnormality. The main reason for the deformity does not lie in the race of human being. The root cause is a genetic mutation. The polypeptide chain of hemoglobin consists of two alpha chains and two beta chains. In sickle cells, the glutamate amino acid in the sixth position of the beta chain is replaced by valine. Glutamate is a negatively charged amino acid whereas valine is non polar and hydrophobic. It therefore causes hydrophobic interactions among the other beta chains subsequently leading to sticking together of proteins. Since, the genetic mutation is present in the DNA (Deoxyribonucleic acid) it subsequently gets passed on from generation to generation. Sickle cell anemia is a recessive disorder. Therefore a person carrying a normal copy of hemoglobin can still survive to produce progeny. However, if the children receive two defective copies from either parent, then they develop sickle cell disease. However, the main reason for the persistence of high number of sickle cell individuals in Africa can be attributed to the presence of the Malaria parasite.