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Basic Mendelian Genetics What lovely things we pass onto our children!
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Mendel’s Laws Law 1: Law of Unit Characteristics –Inherited traits are controlled by “factors” which occur in “pairs”. Factors = __________ Pairs = __________ Law 2: Law of Dominance –One allele hides another allele in a heterozygote Stronger allele = _____________ Weaker allele = _____________
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Mendel’s Laws Continued Law 3: Law of Segregation –Alleles of a gene are separated during gamete formation Each cell only gets 1 allele for a gene A a Bb
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Mendel’s Laws Continued Law 4: Law of Independent Assortment of Alleles –When alleles separate during meiosis, they do so independently of alleles of other genes Placement of alleles is random Not influenced by other genes A A B B a a b b
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Mendel’s Laws Continued Law 5: Law of gene pricing –Lee genes are usually less expensive than Levi’s, except when Levi’s are on sale
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Life Beyond the Law of Dominance Not all traits are governed by the law of dominance Incomplete Dominance –Neither allele is completely dominant over the other in the heterozygote Blending/Mixing Ex) Snap dragons WW – White flowers RR – Red Flowers RW – Pink Flowers
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Incomplete Dominance
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Life Beyond the Law of Dominance Codominance –Both genes express themselves FULLY at the same time Example: Roan cattle RR = Red Hair WW = White Hair RW = Roan (both red + white) Example 2: Blood type in humans (AB)
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Life Beyond the Law of Dominance Multiple Alleles –A gene possessing more than 2 alleles Example: Blood types Blood types differ in antigens found on RBC’s AA – Homozygous AType A BB – Homozygous BType B OO – Homozygous OType O AO – Heterozygous AType A BO – Heterozygous BType B AB – Heterozygous AB Type AB
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Life Beyond the Law of Dominance Polygenic Inheritance –When a trait is controlled by more than 2 genes Example: Eye color (3 genes) Amount of pigment Location of pigment Tone of pigment
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Cowboys denied home field by Eagles
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A Review of Mendelian Genetics 1)Neither allele is dominanta) Complete Dominance 2)More than 2 allelesb) Codominance 3)Both alleles are dominantc) Incomplete dominance 4)Many genes code for 1 traitd) Multiple alleles 5)One allele is dominante) Polygenic inheritance
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