BME 80H Lecture Notes - Lecture 11: Abo Blood Group System, Glycosyltransferase, Antigen
11 Jun 2018
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11th lecture- Exceptions to the Rules (ch. 3, p. 63-64/61-62; ch. 17, p. 381-382/377-378;
ch2 p. 26-27/24-25; ch 4, p. 78-79/76-77, 84-85/82-84; ch. 15, p. 330-332/326-328)
Exceptions to Mendel's Laws (Handout: Table 5.2 from Lewis, 5th ed.)
I. Exceptions when considering a single genetic locus
A. Polymorphic loci- Genes with Multiple Alleles (>2 alleles in a
population)
Example: ABO Blood group
1. Complete dominance and Codominance
complete dominance = one allele is dominant while the other is
recessive. Follows Mendel’s Law of Dominance.
codominance = each allele is expressed equally in the phenotype.
The "I" gene encodes an enzyme (ABO Glycosyltransferase) involved in
adding sugars to a component (the H antigen) presented on the surface
of red blood cells (RBCs). (figure 3.19/3.17).
-I^A allele: attaches the “A” sugar
-I^B allele: attaches the “B” sugar
-I^O allele: no enzyme made, so no sugars are attached
These different sugars serve as antigens (table 17.4, figure 17.13).
-antigen is a substance that triggers an immune response (production of
antibodies) because it is seen as non-self
2. Dominance Hierarchies at polymorphic alleles
Example: Coat color in rabbits
C allele = full color
cch allele = chinchilla (light grayish)
ch allele = Himalayan, albino with black extremities
c allele = albino
Dominance hierarchy: C> cch> ch >c
find more resources at oneclass.com
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Document Summary
17, p. 381-382/377-378; ch2 p. 26-27/24-25; ch 4, p. 78-79/76-77, 84-85/82-84; ch. Exceptions to mendel"s laws (handout: table 5. 2 from lewis, 5th ed. : exceptions when considering a single genetic locus, polymorphic loci- genes with multiple alleles (>2 alleles in a population) Example: abo blood group: complete dominance and codominance complete dominance = one allele is dominant while the other is recessive. Follows mendel"s law of dominance. codominance = each allele is expressed equally in the phenotype. The i gene encodes an enzyme (abo glycosyltransferase) involved in adding sugars to a component (the h antigen) presented on the surface of red blood cells (rbcs). (figure 3. 19/3. 17). I^o allele: no enzyme made, so no sugars are attached. These different sugars serve as antigens (table 17. 4, figure 17. 13). Antigen is a substance that triggers an immune response (production of antibodies) because it is seen as non-self: dominance hierarchies at polymorphic alleles.
