- Unit 6: Inheritance Part 2: Complex Patterns of Inheritance.
Unit 6: Inheritance Part 2: Complex Patterns of Inheritance.
<ul><li><p>Unit 6: InheritancePart 2: Complex Patterns of Inheritance</p></li><li><p>Extending Mendelian geneticsMendel worked with a simple systempeas are genetically simplemost traits are controlled by single geneeach gene has only 2 versions1 completely dominant (A) (complete dominance)1 recessive (a)Examples: albinism, earlobes, tongue rolling</p><p>But its usually not that simple!</p></li><li><p>Incomplete dominanceHybrids have in-between appearanceFRFR = red flowersFrFr = white flowersFRFr = pink flowersmake 50% less colorFRFRFRFrFrFrIn humans, hypercholesterolemia is an example of incomplete dominance.CHCH= normalCHCh= elevated cholesterol (2xs the normal levelChCh= extremely high cholesterol (5xs the normal level, VERY dangerous).Packet p. 11Practice on 12</p></li><li><p>Codominance (& multiple alleles)Equal dominance (expressed equally)human ABO blood groups3 versions IA, IB, iA & B alleles are codominantboth A & B alleles are dominant over i allelethe genes code for different carbohydrate "flags" on the surface of red blood cellsPacket p. 11Practice on 12 & 13</p></li><li><p>Blood donationclottingclottingclottingclottingclottingclottingclotting</p></li><li><p>PleiotropyOne gene can have many effects.eg sickle cell </p></li><li><p>Many genes: one characterPolygenic inheritanceadditive effects of many geneshumansskin colorheighteye colorintelligencebehaviorsPacket p. 11</p></li><li><p>Polygenic inheritanceMultiple genes affect one trait.Human skin color is controlled by at least 3 genes, each with at least two alleles.This Punnett square shows the potential offspring skin tones in the F2 generation, crossing two individuals who are triple heterozygotes.</p></li><li><p>Polygenic inheritanceEye color is controlled by 4 known genes and probably multiple othersAt least 3 pigment genesBrown (B) dominant to blue (b) and to G & g (below)Green (G) dominant to blue (g)Melanin</p><p>At least 1 structural gene</p></li><li><p>Linked genesSo far we have talked about independent assortment, which is</p><p>But, some genes ARE inherited together</p><p>On autosomal chromosomes, we call these linked genes</p><p>On sex chromosomes, we call these sex-linked genes</p></li><li><p>Sex-linked genesX-linkedRecessive: hemophilia, red-green colorblindnessRecessive traits are more common in males. Why?There are very few disorders that are X-linked dominant. Why do you think?</p></li><li><p>PedigreesPedigrees are family trees that show the presence/absence of specific traits or diseases.Squares represent malesCircles represent femalesFilled shapes represent the presence of a trait or diseaseSome pedigrees show carriers (half-filled shapes)</p><p>If this pedigree tracks the presence of an autosomal homozygous recessive trait, what are the genotypes of the very first parents at the top?</p><p>******Phenylketonuria (mutated enzyme leads to mental retardation and reduced hair and skin pigmentation)***Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors.These proteins normally slow and then stop bleeding.Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly.Bleeding in muscles and joints can be painful and lead to serious damage.Individuals can be treated with intravenous injections of the missing protein.</p><p>*</p></li></ul>