Paper No. : 08 Human Population Genetics Module : 06 Mendelian Inheritances in Man Development Team Prof. Anup Kumar Kapoor Principal Investigator Department of Anthropology, University of Delhi Paper Coordinator Prof. Gautam K. Kshatriya Department of Anthropology, University of Delhi Content Writer Tabitha Panmei Department of Anthropology, University of Delhi Prof. A.Paparao Sri Content Reviewer Venkateswara University, Tirupati, Andhra Pradesh 1 Human Population Genetics Anthropology Mendelian Inheritance in Man Description of Module Subject Name Anthropology Paper Name 08Human Population Genetics Module Name/Title Mendelian Inheritance in Man Module Id 06 2 Human Population Genetics Anthropology Mendelian Inheritance in Man Table of Contents 1. Introduction 2. Mendel’s law a) Law of Segregation (the First Law) b) Law of Independent Assortment (the Second Law) c) Law of Dominance (the Third Law) 3. Mendelian Traits and Non-Mendelian Traits 4. Background Information 5. Genetic Mapping of Mendelian characters 6. Mendelian and Atypical patterns of inheritance 7. Useful genetics Vocabulary 8. Misconception Regarding Dominance and Recessiveness 9. Mendelian Inheritance in man and its online version, OMIM Learning Outcomes of the study After studying of this module: You shall be able to understand how Mendelian inheritance first discovered and the important role play in human body. Shall understand the difference of Mendelian traits and Non-Mendelian traits. You would be able to identify the differences of dominant and recessive inheritance occurred in man. You would be able understand how the hereditary diseases occur through generation to another. You would be able to understand how Mendelian Inheritance in man and its online version, OMIM. 3 Human Population Genetics Anthropology Mendelian Inheritance in Man Mendelian Inheritance in Man 1. Introduction Mendelism is the system of heredity formulated from Mendel’s conclusions. Gregor Mendel is known as the father of modern genetic because of his experiment with pea plants which gave the basic insights and vocabulary to pattern of genetic .Briefly summarized, as we understand it today by means of the science of genetics, the mendelism system states that an inherited characteristic is determined by the combination of a pair of hereditary Units, or gene, one from each of the paternal reproductive cells, or gametes. Mendel used a statistical analysis of large populations of plant offspring to identify all possible expressions of basic genetic trait. More than 11,000 Mendelian disordered have been revealed. Mendelian disorders have been propounded by Australian botanist Gregor Mendel (1822,84). Mendel’s developed some of the concepts that we now. Some of the terms are given below: Table 1.1 showing Mendel concepts Dominant Express even if only one factors is inherited from one parent. Recessive Inherit one factor from each parent in order for expression to occur. Allele Different forms of the same gene. Homozygous Offspring inherit matching alleles, one from each parent. Heterozygous Offspring inherit non-matching alleles, one from each parent. Genotype The sum of all genes, many which will not ever be expressed. Phenotype The part of the genetic constitution that is expressed. Humans are not so simple and although many of their traits are dominant or recessive patterns, many others are multiple alleles, co-dominant, or other expressedpatterns. Mendelian inheritance is based on transmission of a single gene on a dominant recessive or X-linked pattern. Mendel's Genetics For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrid. It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown. Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half. By the 1890's, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction. The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children. A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right. His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death. His early adult life was spent in relative obscurity doing basic genetics research and teaching high school mathematics, physics, and Greek in Bruno. In his later years, he became the abbot of his monastery and put aside his scientific work. 4 Human Population Genetics Anthropology Mendelian Inheritance in Man While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms.While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms. 1. Mendelian Law’s a) Law of Segregation (the First Law)- The law of Segregation states that every individual contains a pair of alleles for each particular trait which segregate or separate during cell division (assuming diploid) for any particular trait and that each parent passes randomly selected copy (allele) to its offspring. The offspring then receives its own pair of alleles of the gene for that trait by inheriting sets of homologous chromosomes from the parent organisms. Interaction between alleles at single locus termed dominant and these influence how the offspring expresses that trait. During game, the allele for each segregation from each other so that gametes carries only one allele for each gene. b) Law of Independent Assortment (the Second Law)-It is state that in the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair heritance Law of traits are distributed to the gametes. The law of Independent Assortment, also known as Inheritance Law which states that separate genes for separate traits are passed dependent and independently of one another from parents to children. The biological selection of a particular gene in the gene pair for one trait to be passed to the offspring has nothing to do with the selection of the gene for any other trait. More precisely, the law state that if the different allele genes assort independently of one another during gamete formation. Genes for different traits can segregate independently during the formation of gametes. c) Law of Dominance (the Third Law)-The third law state that recessive alleles will always be masked by dominant allele. A cross between homozygous dominant and homozygous recessive will always express the dominant phenotype, while still having a heterozygous genotype. It can explained easily with the help of a mono hybrid cross experiment. It is important to note that the law of dominance is significant and true but is not universally applicable. According to the latest revisions, only two of the rules are considered to be laws. The third one is considered as a basic principle but not a genetic law of Mendel. Some alleles are dominant while other recessive, an organism with at least one dominant allele will display the effect of the dominant allele. 2. Mendelian Traits: In earlier studies, some physical attributes of humans were considered Mendelian in nature, but further study suggested they are in fact not. These traits may involve more complex genetic models that usually include more than one gene. Mendelian traits are passed on to the offspring through the 5 Human Population Genetics Anthropology Mendelian Inheritance in Man recessive pattern of inheritance or through the dominant pattern. The recessive inheritance pattern needs both parents to have the genes, and offspring must inherit a gene from each parent to display the trait. Through the dominant pattern of inheritance, only one copy of the gene needs to be inherited by a child to display the trait. In the case of autosomal genes the child can inherit the gene from either parent. Mendelian Traits are traits which follow Mendel’s rules of only two possible versions (dominant and recessive traits). Table2.1.Showing Mendelian traits characteristic Finger Hair Having fingers hair (between knuckles) is dominant over lacking finger hair. Tongue Rolling Ability to roll tongue into a “u” shape is dominant over not being able to roll tongue. Earlobes Free earlobes are dominant over attached earlobes Dimples Dimples are dominant over no dimple. Roman nose A nose with a bump is dominant over a straight nose. Shapes of hairline Widow’s peak is dominant over no widow’s peak. PTC Ability to taste PTC is dominant over inability to taste PTC 3. Non-Mendelian trait: Mendel explained inheritance in terms of discrete factors- gene- that are passed a long from generation to generation according to the rules of probability. Mendel’s laws are valid for all sexually reproducing organisms, including garden peas and human beings. However, Mendel’s law stop short of explaining some patterns of genetic inheritance. For most sexually reproducing organisms, cases where Mendel’s laws can strictly account for the patterns of inheritance are relatively rare. Often the inheritance patterns are more complex. The F1 offspring of Mendel’s pea crosses always looked like one of the two parental varieties. In this situation of “complete dominance”, the dominant allele had the same phenotype effect whether present in one or two copies. But for some characteristics, the F1 hybrid had an appearance in between the phenotypes of the two parental varieties. In Mendelian inheritance, genes have only two alleles, such as a and A. In nature, such genes exist in several different forms and are there for said to have multiple alleles.