BIOL1103Hereditary GeneticsLecture NotesPigment deposition gene: E allele: pigment deposition normal (dominant), e allele: pigment distribution blocked (recessive).Phenotypes: Black fur: BB EE, BB Ee, Bb EE, Bb Ee. Brown fur: bb EE, bb Ee. Yellow fur: BBee, Bb ee, bb ee.If the Labrador is recessive for the e allele, it will be yellow or white.A single character may be influenced by many genesMany characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes.Human skin colour is an example of polygenic inheritance.Pleiotropy occurs when one gene influences many characteristics; sickle cell is an example of human pleiotropy.Cells lose elasticity and die, and they can’t move through capillaries. Organ damage, brain damage, etc. Single point mutation.Phenotypes distribute as a bell curve (normal distribution).Height is also a polygenic effect.PleiotropyAlbinism is an example.Failure to convert tyrosine into melanin.Affects multiple characteristics. (hair, eyes, skin etc).The environment affects many charactersMany characters result from a combination of heredity and the environment. For example, skin colour is affected by exposure to sunlight, susceptibility to diseases, such as cancer has hereditary and environmental components, and identical twins show somedifferences.Only genetic influences are inherited.Walden mentioned this.Chromosome behaviour accounts for Mendel’s lawsThe chromosome theory of inheritance states that genes occupy specific loci (positions) on chromosomes.Chromosomes undergo segregation and independent assortment during meiosis.Mendel’s laws correlate with chromosome separation in meiosis.The law of segregation depends on the separation of homologous chromosomes in anaphase I.