NOTES – Complex NOTES – Complex Inheritance PatternsInheritance Patterns
Most human traits have more than 2 or 3 Most human traits have more than 2 or 3 forms. Types of inheritance that are more forms. Types of inheritance that are more complex than simple dominance, complex than simple dominance, incomplete dominance or codominance incomplete dominance or codominance control these traits.control these traits.
Multiple Allelic InheritanceMultiple Allelic Inheritance (Multiple (Multiple
Alleles)Alleles) Traits are controlled by 1 gene with Traits are controlled by 1 gene with more more
than 2than 2 alleles alleles
Ex. The ABO Blood Type System in HumansEx. The ABO Blood Type System in Humans
The gene that controls ABO blood type has 3 The gene that controls ABO blood type has 3 alleles:alleles:
AA = Type A blood = Type A blood BB = Type B blood = Type B blood oo = Type O Blood = Type O Blood
Alleles Alleles AA and and BB are are codominantcodominant and allele and allele oo is is recessiverecessive
There are 6 possible genotypes and 4 There are 6 possible genotypes and 4 possible phenotypes:possible phenotypes:
A A or A oA A or A o == Type A BloodType A Blood
B B or B oB B or B o = = Type B BloodType B Blood
ABAB == Type AB BloodType AB Blood
o o o o = = Type O BloodType O Blood
Blood CellsBlood Cells
There are four basicThere are four basic Blood Blood typestypes: :
Type AType A with A antigens on with A antigens on the red cells and anti B the red cells and anti B antibodies in the plasma. antibodies in the plasma.
Type BType B with B antigens on with B antigens on the red cells and anti A the red cells and anti A antibodies in the plasma. antibodies in the plasma.
Type ABType AB with both A and B with both A and B antigens on the red cells antigens on the red cells and no blood type and no blood type antibodies in the plasma. antibodies in the plasma.
Type O Type O with no antigens on with no antigens on the red cells and both anti A the red cells and both anti A and anti B antibodies in the and anti B antibodies in the plasma plasma
Polygenic InheritancePolygenic Inheritance
Traits are controlled by Traits are controlled by more than 1more than 1 genegene
There are many possible phenotypesThere are many possible phenotypes Ex. Skin color is controlled by at least Ex. Skin color is controlled by at least
3 genes 3 genes A = dark skinA = dark skin a = light skina = light skin B = dark skinB = dark skin b = light skinb = light skin C = dark skinC = dark skin c = light skinc = light skin
Differences in skin color are largely Differences in skin color are largely due to differences in the amount of due to differences in the amount of melanin, a dark pigment produced by melanin, a dark pigment produced by skin cells.skin cells.
Each “dark skin” allele (A, B, C) codes Each “dark skin” allele (A, B, C) codes for high melanin productionfor high melanin production
Each “light skin” allele (a, b, c) codes Each “light skin” allele (a, b, c) codes for low melanin productionfor low melanin production
Each dark skin allele (A, B, C) in the Each dark skin allele (A, B, C) in the genotype adds a small but equal genotype adds a small but equal amount of pigment to the skinamount of pigment to the skin
Some possible genotypes and Some possible genotypes and phenotypes:phenotypes:
aabbccaabbcc == very light skin very light skin AABBCCAABBCC == very dark skinvery dark skin AaBbCcAaBbCc = = medium skin medium skin
What would a Punnett Square What would a Punnett Square for skin color look like?for skin color look like?
Cross two medium skin tone parentsCross two medium skin tone parents
AaBbCcAaBbCc X X AaBbCcAaBbCc
Each parent could produce 8 different Each parent could produce 8 different possible combination to pass on: possible combination to pass on: ABC, ABc, AbC, Abc, aBC, aBc, abC, or ABC, ABc, AbC, Abc, aBC, aBc, abC, or abcabc
Blood Type Is PolygenicBlood Type Is Polygenic
Another level of specificity is added to Another level of specificity is added to blood type by examining the presence or blood type by examining the presence or absence of the Rh proteinabsence of the Rh protein Each blood type is either positive "+" (has the Each blood type is either positive "+" (has the
Rh protein) or negative "-" (no Rh protein) Rh protein) or negative "-" (no Rh protein) For example, a person whose blood type is "A For example, a person whose blood type is "A
positive" (A +), has both type A and Rh positive" (A +), has both type A and Rh proteins on the surface of their red blood cells proteins on the surface of their red blood cells
The Rh protein gene has two alleles:The Rh protein gene has two alleles: RR = protein present (+) = protein present (+) rr = protein absent = protein absent
(-) (-)
Polygenic Blood TypePolygenic Blood Type
What is the phenotype of a person who What is the phenotype of a person who has the blood type genotype ABRr?has the blood type genotype ABRr? Type AB +Type AB +
What is the phenotype of a person who What is the phenotype of a person who has the blood type genotype oorr?has the blood type genotype oorr? Type O – Type O –
What would be the genotype of a What would be the genotype of a person who is A +person who is A + AARRAARR or or AoRRAoRR or or AARrAARr or or AoRrAoRr