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NOTES – Complex Inheritance Patterns

NOTES – Complex Inheritance Patterns. Most human traits have more than 2 or 3 forms. Types of inheritance that are more complex than simple dominance, incomplete dominance or codominance control these traits. Traits are controlled by 1 gene with more than 2 alleles

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NOTES – Complex Inheritance Patterns

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  1. NOTES – Complex Inheritance Patterns Most human traits have more than 2 or 3 forms. Types of inheritance that are more complex than simple dominance, incomplete dominance or codominance control these traits.

  2. Traits are controlled by 1 gene with more than 2 alleles Ex. The ABO Blood Type System in Humans The gene that controls ABO blood type has 3 alleles: A = Type A blood B = Type B blood o = Type O Blood Alleles A and B are codominant and allele o is recessive Multiple Allelic Inheritance (Multiple Alleles)

  3. There are 6 possible genotypes and 4 possible phenotypes: • A A or A o = Type A Blood • B B or B o = Type B Blood • AB = Type AB Blood • o o = Type O Blood

  4. Blood Cells

  5. There are four basic Blood types: • Type A with A antigens on the red cells and anti B antibodies in the plasma. • Type B with B antigens on the red cells and anti A antibodies in the plasma. • Type AB with both A and B antigens on the red cells and no blood type antibodies in the plasma. • Type O with no antigens on the red cells and both anti A and anti B antibodies in the plasma

  6. Polygenic Inheritance • Traits are controlled by more than 1 gene • There are many possible phenotypes • Ex. Skin color is controlled by at least 3 genes • A = dark skin a = light skin • B = dark skin b = light skin • C = dark skin c = light skin

  7. Differences in skin color are largely due to differences in the amount of melanin, a dark pigment produced by skin cells. • Each “dark skin” allele (A, B, C) codes for high melanin production • Each “light skin” allele (a, b, c) codes for low melanin production • Each dark skin allele (A, B, C) in the genotype adds a small but equal amount of pigment to the skin

  8. Some possible genotypes and phenotypes: • aabbcc = very light skin • AABBCC = very dark skin • AaBbCc = medium skin

  9. What would a Punnett Square for skin color look like? • Cross two medium skin tone parents • AaBbCc X AaBbCc • Each parent could produce 8 different possible combination to pass on: ABC, ABc, AbC, Abc, aBC, aBc, abC, or abc

  10. Blood Type Is Polygenic • Another level of specificity is added to blood type by examining the presence or absence of the Rh protein • Each blood type is either positive "+" (has the Rh protein) or negative "-" (no Rh protein) • For example, a person whose blood type is "A positive" (A +), has both type A and Rh proteins on the surface of their red blood cells • The Rh protein gene has two alleles: • R = protein present (+) r = protein absent (-)

  11. Polygenic Blood Type • What is the phenotype of a person who has the blood type genotype ABRr? • Type AB + • What is the phenotype of a person who has the blood type genotype oorr? • Type O – • What would be the genotype of a person who is A + • AARR or AoRR or AARr or AoRr

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