Introduction to Complex Mendelian Inheritance PDF

It is rare, but some human traits follow Mendelian patterns of inheritance (Complete dominance) Albinism Webbed fingers Achondroplasia  Recessive Disorders Recessively inherited disorders show up only in homozygous recessive individuals Carriers –heterozygous, ph...

It is rare, but some human traits follow Mendelian patterns of inheritance (Complete dominance) Albinism Webbed fingers Achondroplasia  Recessive Disorders Recessively inherited disorders show up only in homozygous recessive individuals Carriers –heterozygous, phenotypically normal – Tay-Sachs – Cystic fibrosis – Sickle-cell anemia – Albinism Fig. 14-16 Albinism Parents Normal Normal Aa Aa Sperm A a Eggs AA Loading… Aa A Normal Normal (carrier) Aa aa a Normal (carrier) Albino  Dominant Disorders Achondroplasia Most people in US are homozygous recessive Fatal dominant disorders are rare – No carrier state – Huntington’s disease More common due to late expression Fig. 14-17 Parents Small Normal person Dd dd Sperm D Loading… d Eggs Dd dd d Sm. Normal person Dd dd d Normal Sm. person  Inheritance may deviate from simple Mendelian patterns (complete dominance): 1. Environment influences phenotype 2. Multiple genes for one trait 3. Multiple alleles for one trait 4. Incomplete dominance 5. Co-dominance Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Incomplete dominance Both alleles expressed to some degree  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 23.13 A person with straight hair A person with naturally curly (H1H1) hair (H1H1) (H2, H2) ♂ Heterozygous Parents (H1 H2) ♀ Key H1 H1 H2 H2 Straight hair Wavy hair oocytes Curly hair ♀ ♂ H H 1 2 H H1 H1 Phenotypic Ratio sp 1 H1 H2 1 er 2 m 1 H H1 H2 2 H2 H2 Offspring (man): © Vol. 88/PhotoDisc; (woman): © Larry Williams/Corbis Multiple allele Inheritance Human blood groups exhibit co-dominance and complete dominance  Polygenic inheritance additive effect of two or more genes on a single trait Quantitative characters Skin color  Pleiotropy – Gene with multiple phenotypic effects – Sickle cell anemia affects hemoglobin and blood cell shape, also affects other traits Loading… Epistasis - gene at one locus alters the phenotypic expression of a gene at a second locus One gene codes for color and another determines whether pigment is deposited  Environmental effects Multifactorial – Expression of genes can be influenced by environmental conditions Acidic soil Basic soil