Lecture 11 SLIDES

Nurture alleles on same chromosome two alleles

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Unformatted text preview: lleles • Sex-Linked Traits • Maternal Inheritance • Polygenic Traits • Epistasis • Nature vs. Nurture alleles on same chromosome two alleles combine for intermediate phenotype both alleles equally expressed more than two alleles for one gene some genes on X chromosome mutation in mitochondria or chloroplasts more than 1 gene contribute to a trait 1 gene mutation can mask another environmental impact on phenotypes F1 Generation YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Sperm Sperm 1⁄ 2 1⁄ 4 alleles on same chromosome YR 1⁄ 4 Yr 1⁄ 4 yR 1⁄ 4 yr YR 1⁄ 2 yr 1⁄ 4 Eggs YR YYRR Yr YYRr YyRR YyRr F2 Generation (predicted offspring) Eggs 1⁄ 2 YR YYRR YyRr 1⁄ 4 YYrr YYrr YyRr Yyrr 1⁄ 2 yr YyRr 3⁄ 1⁄ yyrr 1⁄ 4 yR YyRR yr YyRr 9⁄ 16 3⁄ 16 YyRr yyRR yyRr 4 4 1⁄ 4 Phenotypic ratio 3:1 Yyrr 3⁄ 16 yyRr 1⁄ yyrr 16 Phenotypic ratio 9:3:3:1 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 Exceptions to Mendelian Inheritance Exceptions to Mendelian Inheritance • Codominance • Incomplete Dominance two alleles combine for intermediate phenotype two alleles are equally dominant and are coexpressed Human ABO Blood Groups 4 blood groups (phenotypes) come from the combinations of 3 alleles for an enzyme (genotype) Table 14.2 Exceptions to Mendelian Inheritance • Sex-Linked Traits Exceptions to Mendelian Inheritance • Maternal Inheritance some genes on X chromosome mutation in mitochondria or chloroplasts Examples of mitochondrial disease include an eye disease called Leber's hereditary optic atrophy; a type of epilepsy called MERRF which stands for Myoclonus Epilepsy with Ragged Red Fibers; and a form of dementia called MELAS for Mitochondrial Encephalopathy, Lactic Acidosis and Stroke-like episodes Exceptions to Mendelian Inheritance • Polygenic Traits more than 1 gene contributes to a trait Exceptions to Mendelian Inheritance • Epistasis 1 gene mutation can mask another Mouse Coat Color Skin color is a multigenic trait and has an additive effect on skin phenotype Must have dominant version of C gene to deposit pigments encoded by B genes. C is EPISTATIC to B! Offspring acquire genes inherited on chromosomes Genes Chromosomal Inheritance - units of heredity (“factors”) -  segments of DNA, located on chromosomes Same gene detected on pair of homologous chromosomes Chapter 15 Figure 15.1 The Chromosomal basis of Mendel’s Laws Mendelian inheritance has its physical basis in the behavior of chromosomes 1857 Mendel’s Laws on Genetic Basis of Inheritance 18...
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