CHAPTER 12Extensions Of Mendelian Genetic Analysis.ppt

Multiple Alleles 1. Not all genes have only two forms (alleles); many have multiple alleles. No matter how many alleles for the gene exist in the multiple allelic series, however, a diploid individual will have only two alleles, one on each homologous chromosome. Fig. 12.1 Allelic forms of a gene ABO Blood Groups 1. ABO blood groups are important in blood transfusions, and result from a series of three alleles (IA, IB and i) that combine to produce four phenotypes (A, B, AB and O). 2. Both IA and IB are dominant to i, while IA and IB are codominant to each other. The resulting phenotypes are (Table 12.1): a. People with genotype i/i are blood type O. b. People with genotype IA/IA or IA/i are blood type A. c. People with genotype IB/IB or IB/i are blood type B. d. People with genotype IA/IB are blood type AB. 3. ABO inheritance follows Mendelian principles. For example, a type O individual’s genotype is i/i. Possible genotypes of the parents could be: a. i/i and i/i (both blood type O). b. IA/i and i/i (one type A, the other type O). c. IA/i and IA/i (both type A). d. IB/i and i/i (one type B, the other type O). e. IB/i and IB/i (both type B). f. IA/i and IB/i (one type A, the other type B). 4. Blood typing may be used in cases of disputed parentage. Blood typing does not prove the identity of a parent. It can, however, eliminate individuals who are not biological parents of a particular child. Example: a. A child with blood type AB (IA/IB) could not have a parent with type O (i/i). Blood type data are not considered adequate legal proof for parenthood in most states, and DNA fingerprinting is generally used. iActivity: Was She Charlie Chaplins Child? Drosophila Eye Color 1. Drosophila has over 100 mutant alleles at the eye-color locus on the X chromosome. Example designations for alleles at this locus: a. The white-eyed variant allele is designated w. b. The wild-type (brick red) allele is w+ . c. A recessive allele, we, produces eosin (reddish-orange) eyes.