O allele is very prevalent in south africa complex

This preview shows page 7 - 9 out of 14 pages.

O allele is very prevalent in South Africa.Complex inheritance patterns- Additions to Mendelian geneticsIn epistasis, genes interact, with the activity of one gene influencing the activity of another.In polygenic inheritance, a character is controlled by the common effects of several genes.In pleiotropy, two or more characters are affected by a single gene.EpistasisGenes interact.Allele of one locus inhibits or masks the effects of an allele at a different locus.Some expected phenotypes do not appear among offspring.All horses start with being either chestnut or black, but a another gene controls whetherthe pigment makes it into the fur.Epistatic reactions also occur in humans; (red hair).Might be the basis for many human disorders. (Diabetes, cancer, cystic fibrosis, etc).Labrador RetrieversMelanin pigment gene: B allele: black fur colour (dominant), b allele: brown fur colour (recessive).
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.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture