A and S are two alleles of the -globin gene, as shown in the graph below Phenoty

Question

A and S are two alleles of the -globin gene, as shown in the graph below Phenotypes at Different Levels of Analysis Normal Carrier AS B-globin polypeptide Red blood cell shape at sea level Sickded cells Normal- Normal- Red blood cel at sea level Red blood cel shape at high atitudes Normal.. Red blood cell at high alttudes Normal Lower ow, anemia to malaria Normal Match the dominance relations of allele A and S at each level of analysis. (Select I,II, III or IV) *Note: IV refers only to the "Red blood cell concentration at high altitude" phenotype and not the "Red blood cell shape at high altitude" phenotype A is dominant, S is recessive A and S show incomplete dominance S is dominant, A is recessive A and S are codominant

Explanation / Answer

Dominance in genetics is a relationship between alleles of one gene, in which the effect on phenotype of one allele masks the contribution of a second allele at the same locus.The first allele is dominant and the second allele is recessive. For genes on an autosome the alleles and their associated traits are autosomal dominant or autosomal recessive. Dominance is a key concept in Mendelian inheritance and classical genetics. Often the dominant allele codes for a functional protein whereas the recessive allele does not.A classic example of dominance is the inheritance of seed shape in peas. Peas may be round, associated with allele R or wrinkled associated with allele r. In this case, three combinations of alleles are possible: RR, Rr, and rr. The RR individuals have round peas and the rr individuals have wrinkled peas. In Rr individuals the R allele masks the presence of the r allele, so these individuals also have round peas. Thus, allele R is dominant to allele r, and allele r is recessive to allele R. This use of upper case letters for dominant alleles and lower case ones for recessive alleles is a widely followed convention.

More generally, where a gene exists in two allelic versions three combinations of alleles are possible: AA, Aa, and aa. If AA and aa individual show different forms of some trait and Aa individuals show the same phenotype as AA individuals, then allele A is said to dominate, be dominant to or show dominance to allele a, and a is said to be recessive to A.Dominance is not inherent to either an allele or its phenotype. It is a relationship between two alleles of a gene and their associated phenotypes; one allele can be dominant over a second allele, recessive to a third allele, and codominant to a fourth. Also, an allele may be dominant for a particular aspect of phenotype but not for other aspects influenced by the same gene. Dominance differs from epistasis, a relationship in which an allele of one gene affects the expression of another allele at a different gene.

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