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MODULE - 3 Reproduction and Heredity 21 Notes PRINCIPLES OF GENETICS It is common observation that seeds of mango trees grow into mango plants, dogs give birth to puppies and not into the young ones of any other animal. Humans give birth to human beings. The tendency of offspring to inherit parental characteristics is termed heredity and the science of heredity in Genetics . Genetics also seeks to answer questions like why two offspring of same parents look different, why are some people dark and others light skinned etc. In other words, why is there variation among individuals of the same kind. This lesson deals with heredity and variation. It also includes a section on hereditary disorders and gives an idea of the human genome too. OBJECTIVES After completing this lesson, you will be able to : explain the terms heredity and variation; describe Mendel s experiments on garden pea and the principles derived; define the term hybridization, alleles, trait, dominance, recessive, homozygous, heterozygous, genotype, phenotype; explain the term incomplete dominance with the example of flower colour in 4 o clock plant (Mirabilis jalapa); define the terms lethal genes and pleiotropic genes; explain quantitative (polygenic) inheritance supported by the examples of kernel colour of wheat and skin colour of humans; differentiate between monogenic and polygenic inheritance; explain the chromosome theory of heredity; define and give examples of linkage, crossing over and criss-cross inheritance; justify mitochondrial inheritance as a case of maternal inheritance; describe the human karyotype; differentiate between sex chromosomes and autosomes; BIOLOGY 71
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