Post on 03-Jan-2016
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Chapter 14 – Mendel and the Gene Idea
Gregor Mendel
• Mid 19th century Austrian monk
Garden pea
• Self fertilize or cross fertilize
• True breeding or hybrids
Garden pea traits
Experimental design – monohybrid cross
Terminology • “factors” = genes
– Alleles
• Dominant
• Recessive
Terminology cont
• Phenotype
• Genotype – Homozygous
– Heterozygous
Interpretation of monohybrid cross
• Law of Segregation
Testcross
• To determine genotype of dominant individual
Experimental design – dihybrid cross
• Law of independent assortment
Extensions of Mendelian inheritance
• All of Mendel’s traits were coded for by a single gene and had only two alleles – with one being completely dominant over the other
• Not all traits are that simple
Incomplete dominance
• Heterozygote has an intermediate phenotype
Epistasis
• One gene masks the effects of another gene
Environmental effects
• Phenotype is affected by environmental influence of gene expression
Multiple alleles & Codominance
• Some genes have more than two alleles present in a population
• Codominance – heterozygote expresses both alleles
Blood type cont
• Rh factor – Mendelian inheritance
• “+” completely dominant over “-”
– Erythroblastosis fetalis
Polygenic inheritance
• Continous traits
Pleiotropy
• One gene having multiple effects
Pedigree analysis
Recessive – albinism Dominant – Achondroplasia
Prenatal testing