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Unformatted text preview: B) (BO) (AB) (OO) A gene can have more than two alleles (cont'd.) Lentils offer another example of multiple alleles 5 alleles present that determine coat pattern Marbled1 (m1), marbled2 (m2), spotted (s), dotted (d), clear (c) Basically, some alleles were more dominant than others A priority ranking could be determined m1 > m2> s =d > c Notice that spotted and dotted were equal in dominance A DOMINANCE SERIES was revealed 0 Perform reciprocal crosses between pure breeding lines of all phenotypes Another DOMINANCE SERIES example
0 Genotype Phenotype A_ atat aa agouti Black/ yellow black 0 A > a > a
t A gene can have more than two alleles (cont'd.) 0 Mutations are the source of new alleles Some are good, some are bad. Mutation rates vary tremendously, depending on many factors Allele frequency: total # of gene copies, expresses as a % Wildtype allele: allele frequency > 1% Mutant allele: allele frequency < 1% Monomorphic: gene with only one wildtype allele Every organism carries 2 copies of every allele Plant INCOMPATIBILITY example Alleles determine acceptance or rejection of pollen Idea is that selfpollination in some plants is avoided Again, multiple alleles are used in the pollen and ovules Separate male and female parts on the plant However, each plant can still only carry a maximum of 2 different allele types on one particular plant There are >90 alleles for the incompatibility complex Overall, this promotes variability within the One Gene May Contribute to Several Visible Characteristics Pleiotropy single gene determines more than one distinct and seemingly unrelated characteristics Some alleles may cause lethality (death).
Recessive lethal allele: in certain combinations, some alleles may negatively affect survival of individuals Coat color of mice 0 All yellow mice are heterozygotes: Cross between inbred agouti and yellow mice reveals a 1:1 ratio Yellow mice are therefore AYA heterozygotes 0 Yellow mice do not breed true:
Cross between two yellow mice reveals a 2:1 ratio of yellow to agouti The AY allele (when homozygous) is LETHAL Traits Determined by One Gene: Extensions to Mendel's Ideas Explain Variations on the 3:1 Monohybrid Ratio
0 Table 3.1 Sickle Cell Anemia: Extensions to Single Gene Inheritance Multiple alleles Pleitropy Recessive Lethality Different Dominance Relations 1. MULTIPLE ALLELES Hemoglobin is composed of two polype...
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- Fall '03