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Genetics Unit 6
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Heredity Gene A sequence of nucleotides that code for a specific trait Ex: eye color, blood type Allele Two or more different versions of a gene (trait) Ex: wet earwax versus dry earwax
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Simple (Mendelian) Genetics
Dominant Alleles (represented by capital letters) Recessive alleles (represented by lower case letters) Genotypes Homozygous dominant: BB Homozygous recessive: bb Heterozygous: Bb Phenotypes Either the Dominant or recessive
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Complex Heredity Incomplete Dominance How can you tell?
When the dominant allele is unable to completely mask/hide the recessive allele…so we get a blend of the two alleles How can you tell? When two homozygous individuals have a third different phenotype When the heterozygous is a blend of the homo dom and homo rec
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Complex Heredity Codominance How can I tell?
When there are two alleles that are BOTH dominant End up with BOTH versions of that gene present (like a roan horse or a cow!) How can I tell? When you see BOTH alleles present, NOT blended…but both present!
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Complex Heredity Multiple Alleles How can you tell?
When there are more than two different versions for a gene Ex: blood type How can you tell? More than one letter
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Complex Genetics Sex-linked How can I tell?
When the gene is located on the X chromosome (the 23rd pair in humans)… the chromosome that determines sex. How can I tell? Always written with an X and a superscript (like this: XAXa) More males affected than females EX: calico cats, red-green colorblindness
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Complex Genetics Polygenic How do I tell? Multiple GENES involved
Phenotypes are in a range Ex: skin color, height
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