8 200tt 125tt 325tttt january312007

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Unformatted text preview: show the trait (e.g., round/wrinkled peas), penetrance is complete. ­ Retinoblastoma is the most common form of eyecancer. Although it is a dominant trait, only 75% of cancer. the individuals carrying the allele are affected. In this instance, penetrance is incomplete. instance, January 31, 2007 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 38 Incomplete Penetrance ­ In a certain breed of plants, thorns (T) are determined by a dominant are allele and thornless (t) iis determined by the recessive allele for the thorny s allele gene. However, T is only 80% penetrant in the heterozygotes (i.e., 20% of the heterozygotes will appear thornless). Starting with the parental cross TT x tt, what would be the expected number of phenotypes TT tt what observed in a population of 500 F2 plants? observed T T t TT Tt 125 Tt T t 125 tt 125 125 100% Penetrance T t t TT Tt 125 Tt 100 tt +Tt 100 175 80% Penetrance Total thorny = 250Tt x 0.8 = 200Tt + 125TT = 325Tt+TT Jan...
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